Brewing for Beginners
Objective A very simple explanation of the brewing process.
Index What is beer? ........................................................................................................................ 6 Cereals................................................................................................................................... 6 Barley...................................................................................................................................................................................... 6
Malting ....................................................................................................................................... 8 What is Malt?......................................................................................................................... 8 Why do we malt?.................................................................................................................................................................... 8 Steeping.................................................................................................................................................................................. 9 Germination.......................................................................................................................................................................... 10 Kilning................................................................................................................................................................................... 12 Lager (Pils) malt ................................................................................................................................................................... 13 Vienna malt........................................................................................................................................................................... 14 Crystal malt .......................................................................................................................................................................... 14 Wheat malt............................................................................................................................................................................ 15
Adjuncts .................................................................................................................................. 17 What are adjuncts? ............................................................................................................. 17 So why use Adjuncts? ........................................................................................................ 17 Cost & availability ................................................................................................................................................................ 17 Control of fermentability...................................................................................................................................................... 17 Beer quality and taste can be enhanced............................................................................................................................. 18 Colour contribution.............................................................................................................................................................. 18 Beer presentation................................................................................................................................................................. 18 Affect on stability ................................................................................................................................................................. 18
There are some disadvantages though ............................................................................. 18 Affect on foam...................................................................................................................................................................... 18 Affect on fermentation ......................................................................................................................................................... 19
Solid cereal adjuncts. ......................................................................................................... 19 Page 1 of 95
Liquid adjuncts.................................................................................................................... 19 Raw Sugars .......................................................................................................................................................................... 19 Cereal Syrups....................................................................................................................................................................... 20
Solid blends of natural sugars. .......................................................................................... 20 The Brewhouse ....................................................................................................................... 21 Milling ...................................................................................................................................... 21 Mashing ................................................................................................................................... 24 Enzymes .............................................................................................................................. 24 How does Amylase work in the mash?............................................................................................................................... 25
Mashing, the process.......................................................................................................... 26 Lautering ................................................................................................................................. 28 What does a lauter tun look like? ...................................................................................... 28 Sparge................................................................................................................................................................................... 29 Rakes .................................................................................................................................................................................... 29 Draw off ................................................................................................................................................................................ 30
Operation............................................................................................................................. 30 The mash filter .................................................................................................................... 31 What does it consist of?...................................................................................................................................................... 31
Wort boiling............................................................................................................................. 33 Why boil wort? .................................................................................................................... 33 What does a modern copper look like?............................................................................. 33 Hops......................................................................................................................................... 36 What are hops? ................................................................................................................... 36 Why are hops used in beer?............................................................................................... 37 History ................................................................................................................................. 37 The brewing bit.................................................................................................................... 38 Hop growing ........................................................................................................................ 38 Hop harvesting.................................................................................................................... 43 Summary ............................................................................................................................. 46 Wort clarification..................................................................................................................... 47 Why do we clarify wort? ..................................................................................................... 47 Types of separation system ............................................................................................... 47 Page 2 of 95
Breweries using whole hops ............................................................................................................................................... 47 Hop Back .......................................................................................................................................................................... 47 Hop Strainer ..................................................................................................................................................................... 49 Breweries using hop pellets or extracts ............................................................................................................................. 49 Settling tank...................................................................................................................................................................... 49 Whirlpool........................................................................................................................................................................... 50 Hot Wort Centrifuge ............................................................................................................................................................. 51 What is centrifugal force?.................................................................................................................................................. 51 How does a decanter centrifuge work? ............................................................................................................................. 52
Wort filters ........................................................................................................................... 52 Wort cooling, aeration & yeast pitching ................................................................................ 54 Why do we cool wort? ........................................................................................................ 54 Microbial Contamination ..................................................................................................................................................... 54 Cooling Wort to fermentation temperature......................................................................................................................... 55 Aeration/Oxygenation & yeast growth................................................................................................................................ 57 Why do we aerate? ........................................................................................................................................................... 57 What does aeration achieve?............................................................................................................................................ 57 Where & how should we aerate? ...................................................................................................................................... 57 Ensure that you only use air from an oil free compressor. In any event, the air/oxygen should pass through a sterile filter....................................................................................................................................................................................... 58 Safety .................................................................................................................................................................................... 58 Be aware that pure oxygen can explode in contact with grease. All joints and fittings should be grease (and oil!) free if oxygen is used. ................................................................................................................................................................. 58
Yeast pitching ..................................................................................................................... 58 Formation and separation of cold break. .......................................................................... 59 Yeast ........................................................................................................................................ 61 Reproduction........................................................................................................................................................................ 62
Selecting yeast for Brewing ............................................................................................... 62 Yeast metabolism (growth)................................................................................................. 63 Fermentation ........................................................................................................................... 64 Fermentation in practice..................................................................................................... 66 Temperature ......................................................................................................................................................................... 66 Deep Cooling........................................................................................................................................................................ 66 Process and progress of fermentation ............................................................................................................................... 66 A Saccharometer. ............................................................................................................................................................. 67
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Yeast collection.................................................................................................................................................................... 67
How does yeast do it? ........................................................................................................ 67 Feeding the Fermentation.................................................................................................................................................... 68 Phases of Yeast growth....................................................................................................................................................... 68
Types of fermentation......................................................................................................... 68 Maturation ............................................................................................................................... 71 Why mature beer?............................................................................................................... 71 How do we do it?................................................................................................................. 72 The traditional method......................................................................................................................................................... 72 Modern method .................................................................................................................................................................... 72 Oxygen.................................................................................................................................................................................. 72
Sedimentation ..................................................................................................................... 73 How a centrifuge works. ...................................................................................................................................................... 73
Stabilisation......................................................................................................................... 74 What can we use? ............................................................................................................... 74 Where do we add them? ...................................................................................................................................................... 74
Filtration .................................................................................................................................. 76 Why filter beer?................................................................................................................... 76 What is filtration?................................................................................................................ 76 How do filters work?........................................................................................................... 76 Surface filtration................................................................................................................................................................... 78 Depth filtration ..................................................................................................................................................................... 78
What type of filter should we use? .................................................................................... 80 The Plate and Frame Filter................................................................................................................................................... 80 Candle Filter. ........................................................................................................................................................................ 81 Horizontal Screen Filter. ...................................................................................................................................................... 84 Safety .................................................................................................................................................................................... 85
Carbonation......................................................................................................................... 86 Bright beer............................................................................................................................... 87 Water........................................................................................................................................ 88 Suitability for brewing......................................................................................................... 89 How?..................................................................................................................................................................................... 89 Chlorine ............................................................................................................................................................................ 89 Page 4 of 95
Chlorine dioxide ................................................................................................................................................................ 89 Ozone ............................................................................................................................................................................... 89 UV treatment .................................................................................................................................................................... 89 Sterile Filtration & Distillation ............................................................................................................................................ 89
Removal of solids ............................................................................................................... 90 Minerals & Salts .................................................................................................................. 92 Calcium................................................................................................................................................................................. 92 Magnesium ........................................................................................................................................................................... 92 Sodium.................................................................................................................................................................................. 93 Potassium............................................................................................................................................................................. 93 Iron........................................................................................................................................................................................ 93 Zinc ....................................................................................................................................................................................... 93 Copper ions .......................................................................................................................................................................... 93 Carbonates & bi-carbonate.................................................................................................................................................. 93 Chloride ................................................................................................................................................................................ 94 Sulphate................................................................................................................................................................................ 94 Nitrite & nitrate .................................................................................................................................................................... 94
Water hardness. .................................................................................................................. 94
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What is beer? Beer is an alcoholic drink made from cereals. It is flavoured with: ·
Compounds from the cereal
·
Hops (to give bitterness)
·
And sometimes extra sugars (for flavour and fullness)
It is fermented by yeast. Yeast produces Alcohol and Carbon Dioxide from sugar. The sugar is produced from the cereal during a malting process followed by a brewhouse process. Sometimes non malted adjunct is added as well to provide extract and other advantages. The alcohol gives the intoxicating effect and some flavour to the beer. The Carbon Dioxide gives sparkle and improves the “palate”
Cereals The most common cereal is Barley. Some beers however are made from Wheat (German Weizenbier). Some beer is made from Sorghum. Sorghum is a common crop in Africa. These cereals are malted to prepare them for the brewing process. Other cereals are also processed (but not malted) and included in the brew. These are called adjuncts. They supply fermentable material, but little flavour. We will see later the advantages of using adjuncts as well as malted cereal. Barley There are two types of barley grown. Two row barley and six row barley.
2 Row barley
6 row barley
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These names come from the arrangement of the corns in the ear. Two row barley has 2 lines of corns on the ear:
Looked at from the side
Looked at from the top
Six row barley has 6 lines of corns on the ear Looked at from the side
Looked at from the top
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Malting What is Malt? Malt is barley that has been germinated and dried. Germination starts the production of enzymes: the drying stops them from working until mashing. Why do we malt? The fermentable sugar in barley is “locked up” as starch in the seed. Yeast cannot ferment starch. Fortunately, when cereals start to germinate (grow) they produce biochemicals called enzymes. These enzymes can break down starch to fermentable sugars. When we malt, we want to start germination and produce the enzymes. We germinate the malt in big tanks called steeps. The germinated malt is then put into germinating boxes where it is allowed to start growing. This starts the enzyme production. Nevertheless, we must stop the action of the enzymes before they start to breakdown the starch. If we did not stop them, they would produce sugars. The barley seed would grow and we would lose extract for the brew. Later on in the brewhouse, we will see how we use these enzymes to breakdown the starch to produce a fermentable liquid, wort. We stop the enzymes working by drying the germinated barley carefully. We do this in such a way that the enzymes stop working (they need water to work) but so they are not destroyed (they are sensitive to heat). The barley is dried on a kiln. Kilning also produces a dark colour and the “malty” flavours we expect in beer. Let’s look at the malting process in a little more detail.
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Steeping The first stage of malting increases the water content in the barley grains. The increased water content “tricks” the barley into growing, i.e. starts the germination process. Steeping takes place in a steep tank.
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Steeps seen from below
Barley being sprayed with water in the steep. It is also aerated with compressed air. This improves the germination rate.
After steeping the wet grain is transferred to germinating boxes Germination Towards the end of steeping, the barley starts to grow, to germinate. The rootlet starts to emerge. Germination is done in large, aerated, open vessels. It is done under controlled temperature conditions at approximately 150 C. Air, saturated with water, is passed through the germinating malt. This goes on for a period of three to five days The germinating barley is regularly turned to prevent matting of the rootlets.
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Steeped barley being added to the germinating box.
Barley being turned by machine in the boxes.
A Diagram of a germinating box is shown below.
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While the grain grows, the natural enzymes are produced. When the maltster decides that the time is right (maximum enzymes but before the starch is attacked) the germinated barley is transferred to the Kilns, where it is dried. Kilning During kilning water is removed and flavour compounds formed. Diagram of a kiln
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A malt kiln fully loaded.
The temperature determines the colour of the malt. It also determines the amount of enzymes that survive for use in the mashing process. Heat denatures enzymes. ·
High heat gives high colour and low amount of enzymes.
·
Low heat gives low colour and a high amount of enzymes.
Kilning usually takes between 24 and 36 hours and brings the moisture down to between 3% and 6% Once the malt has been kilned, it can be stored (dry) until it used for brewing. Many different types of malt are made. The most common are the pale malts. They have not been kilned heavily. So there is a maximum amount of enzyme for the brewing process. Here is a typical pale lager malt: Lager (Pils) malt
Other malts are made, sometimes for flavour like Vienna Malt
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Vienna malt
It is produced in a similar way to lager malt, but using higher kilning temperatures (900C) to give a darker colour and slightly stronger nutty, or toffee flavour. Other malts are very dark indeed. They are heated so much that all the enzymes are destroyed, but they give very strong flavours. Crystal malt
Crystal malt has a sweet caramel flavour. It is made by "stewing" green malt. Crystal malt gives beer a ruby red hue. Others are actually roasted to produce a malt where all the contents are caramelised. These are used for British style Stouts. Roasted Malt
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Roasted malt is also called Black malt. It is produced by roasting White Malt at a high temperature. This gives a sharp acrid flavour and a black colour. Roasted malt is used in Sweet Stouts and Dark beers. Wheat is also commonly malted in central Europe to produce “wheat” or “Weizenbier” Wheat malt
After kilning, all malts are cleaned in special “screening” machines before being stored in Silos or bags. A screening machine.
The screens are circular. They rotate and the grain moves along.
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This mesh will separate different grain sizes.
This mesh separates long thin material like stalk from the grain.
The malt is now ready for brewing.
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Adjuncts Before we move on to the brewing process we should look at Adjuncts.
What are adjuncts? Adjuncts are materials that contain fermentable extract. (They may have to be processed before they can be used) Typical adjuncts are: ·
Sugar or syrup.
·
Treated cereal (like maize or rice).
·
Raw starches (such as maize starch).
Most sugars can be fermented directly. All the cereal products have to be treated and added to the brewing process. The natural enzymes in the mash convert them to sugars.
So why use Adjuncts? Cost & availability Adjuncts are used to reduce raw material costs. Another reason can be to utilise local sources of extract. This is especially when locally malted barley is not available. This can happen in tropical areas. Relative cost of selected adjunct (based on malt cost of 100 units): Source of Extract
Relative unit costs
Malt
100
Raw Barley
65
Raw Wheat
70
Maize Grits
86
Control of fermentability Adjuncts can be used to adjust the fermentability of wort. Different sugars ferment at different rates. This affects beer flavour. ·
Glucose ferments rapidly. It gives a thin taste.
·
Maltose ferments more slowly. It gives a fuller taste.
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There is a range of different syrups that can be added to the copper. These syrups have different sugar compositions. Beer quality and taste can be enhanced Bland adjuncts (such as starch and corn syrups) have the effect of diluting malt flavours. As malt flavours are less pronounced, subtler flavours from the fermentation and hops can be tasted. This is typical in some North American beer styles. These beers have up to 50% cereal adjunct. Adjuncts also contribute their own flavours to the beer: ·
Maize gives a fuller flavour.
·
Wheat gives dryness.
·
Rice has a very neutral aroma and taste. It gives a clean lighter tasting beer.
·
Semi-refined cane sugar (Golden Syrup) adds colour and flavour to the beer. It gives a luscious character to ales.
Colour contribution Dark coloured adjuncts are used to provide or adjust the colour of a beer. They may also add flavour. Coloured adjuncts include dark sugars and caramels. Light coloured adjunct will dilute malt colours to produce lighter coloured beers. Light coloured adjunct include rice, pure starches, sugars and other cereals. Beer presentation Some adjuncts such as raw barley and wheat add glycoproteins. These improve foam stability. Affect on stability Most adjuncts are low in Nitrogen. Their use reduces total Nitrogen in the beer. This improves the haze stability of the finished beer.
There are some disadvantages though Affect on foam Some adjuncts are high in lipids (fats), for example maize. Lipids can cause rancid off flavours in the beer. Excess lipids can reduce the amount of foam. Most adjuncts are low in protein. This reduces the total amount of foam proteins available. This reduces the foam potential of the beer. Page 18 of 95
Affect on fermentation When very high levels of adjuncts are used, there is a risk of producing wort with low soluble nitrogen. Soluble nitrogen is needed for healthy yeast growth. Under these circumstances, yeast nutrient may have to be added to the wort. Adjuncts are supplied in three forms
Solid cereal adjuncts. The energy is stored as starch and has to be converted to sugar in the brewhouse during mashing.
Flaked maize
Flaked wheat
Liquid adjuncts. These are already in the form of sugars ready for fermentation. They are generally added directly to the copper Raw Sugars Sugar is available in crude form as sugar cane or as sugar beet. The raw cane sugar is refined through a series of crystallisation and filtrations. A range of liquid and solid sucrose sugars is produced. The less refined the sugar, the darker the colour and the stronger the flavour. The dark coloured sugars give a light caramel, honey, or brown sugar taste. The colour and flavour can be changed by blending in less refined sugar to pure sugar.
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Some brewers prefer to use invert sugar. Invert sugar is a mixture of glucose (also called dextrose) and fructose. It is available in liquid or solid block form. Cereal Syrups Brewing syrups can be manufactured from cereals such as wheat and maize cereals by converting the starch to sugars in a separate process. The syrups are available in liquid form with a range of sugar content. These can be added directly to the copper. Wort fermentability can be adjusted by using different types of syrup.
Solid blends of natural sugars. Added either to the mash copper or after fermentation. The blends can highly fermentable (cane sugar) or at the other extreme purely for flavour (Lactose: a non fermentable sugar)
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The Brewhouse The brewhouse is where we change our malted cereal and cereal adjuncts into a sugary liquid that can be fermented by yeast to make beer. We call the liquid, wort. The conversion is done in large vessels called Lauter tuns. Malt is ground, mixed with warm water and added to the lauter tun. The enzymes (remember them?) in the malt turn the starch into sugar. The sugar dissolves in the water and is ready for boiling and hop addition. We’ll see in a moment that we can use the adjuncts directly in the brewing process. However, the malt has to be prepared for the brewhouse.
Milling Malt when it is delivered to the brewery is of course a whole “seed”. The starch, enzymes and flavours are all locked up in a tight seed coat.
We have to open up the malt to expose the goodies. We do that by milling. There is quite an art in milling. We will see in the next few pages that we not only have to expose the starch but that we also have to provide a filter bed for the lauter tuns. This filter bed is made up of the crushed skin or husk of the malt. It must be just the right size. In addition, it is important that we don’t over-mill the starch. Too fine and it will form a gluey porridge before it can be converted. Too big and we’ll lose extract because not all the starch will be attacked by the enzymes. There are many types of mill. Some are dry mills others are wet mills. The most common dry mill is a six roll (3 pairs) dry mill. When we dry mill the malt is milled to the correct consistency. It is then stored in a hopper over the mashing vessel (we’ll come to that in a moment). The mashing vessel is where it will be mixed with warm water to start the conversion process.
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Three pairs of rolls allow optimum grinding for husk with coarse grits and fine grits. Paired screens below each of the first two sets of rollers divert the various fractions, either to the appropriate set of rolls or direct to the mill outlet. It’s easy to control the different percentages of husk (for filtration in the lauter tun) and grit size of the starch.
Wet milling involves grinding the malt and mixing it with warm water during the milling process. Mashing happens in the mill, not in the mash vessel. We still use a mash vessel though, particularly if we want to use adjuncts. A typical wet mill looks like this. The equipment consists of a steep tank where the entire malt charge for a brew is soaked in water for up to 30 minutes. The amount of water is preset. The soaked malt then passes through a simple two roll mill. Here the endosperm (the starch) is squeezed out. Because the husk is soft, it is not damaged. The milled malt passes directly into the mashing system. Additional water is sprayed in to get the mash consistency correct. Steep water can be re-used as part of the mash. The mash either falls directly into the mash vessel or is pumped to it. There are many variations on these two systems. What both of them do however is to: Page 22 of 95
·
Expose the starch
·
Provide husk for filtration
·
Grind the starch to the correct consistency for best extract and no “setting”
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Mashing Now that we’ve milled out malt we have to start (and control) the process of saccharification. This long word describes the action of the enzymes turning the starch into sugar. Before we go into detail let’s talk about enzymes. We’ve mentioned them before, but what are they? How do they work?
Enzymes ·
Enzymes are proteins that catalyse biochemical re-actions.
·
They are biochemical catalysts. This means that they make a reaction happen but they are left unchanged to repeat the same reaction again and again.
·
Enzymes are specific in the reaction that they catalyse. That is, they only work: ·
On one reaction
·
On one substrate (or target molecule)
Enzyme
SUBSTRATE
Enzyme SUBSTRATE
We can represent an enzyme as having specific sites on its molecule
These coincide with the sites on a target molecule or substrate
The enzyme combines with the target molecule. Because it “fits”, it can start a reaction. You may like to imagine the as substrate being the lock and the enzyme the key.
The enzyme breaks up the substrate. It is left unchanged to work again on another molecule.
In mashing, the substrate is starch. The products of enzymatic action are maltose, glucose, maltotriose and dextrins. The most important enzyme in the malt is Amylase. Page 24 of 95
How does Amylase work in the mash? Let’s imagine this is a starch molecule.
Amylase breaks it up. Most of these sugars are fermentable. They dissolve in the wort.
This sugar is Glucose. It ferments very well. This sugar is Maltose. It ferments well.
This sugar is Maltotriose. (Triose means three). It ferments slowly.
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This sugar is a Dextrin. It does not ferment.
Another important enzyme group is the Proteases. They act on proteins to produce peptides. Peptides in turn are broken down by peptidases to give essential yeast nutrients called amino acids. Amino acids are the building blocks of proteins. Without protein, nothing could grow. For example, yeast needs amino acids to grow.
Mashing, the process The mash tun is where the process of saccharification starts. Saccharification means, “turning to sugar”. Dry grist is mixed with water at a specific temperature in the mashing vessel. Alternatively, already wetted “wet milled” mash may be pumped in. The mash vessel is fitted with an agitator and some sort of heating.
The mash is heated to different temperatures over very carefully controlled time spans. These temperature changes start the saccharification process. They also start other enzyme reactions that produce yeast growth biochemicals from protein in the malt. These different temperatures can be used to change the fermentation characteristics of the beer. For example, a long time at lower temperatures can produce more fermentable sugars. Page 26 of 95
A typical temperature process would look like this
TEMPERATURE/TIME MASH PROFILE FOR PROGRAMMED INFUSION MASH. 100
78
Saccharification 72
65
o
Temp C
75
50
52
Gelatinisation
DP
Transfer to Lauter Tun
25 Mash Tun
20
30 Time in Minutes
5
5
Firstly, the malt starch is allowed to gelatinise (the starch mixes with water and the first enzyme attach makes it soft and sticky). Then the temperature is raised in steps to start saccharification. At the end, the temperature is raised high enough to kill the enzyme activity. The mash is then pumped to the lauter tun. We have to stop the enzyme activity otherwise saccharification would continue and we wouldn’t be able to control the composition of the final wort.
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Lautering Now that we’ve made our mash what next? The mash is now like a thin porridge. It contains bits of husk and other non soluble material. The liquid part is a sticky syrup from all the dissolved sugar. That’s the bit that we want. How do we get it? The answer is the lauter tun!
What does a lauter tun look like?
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Probably the most important thing about the lauter tun is the false bottom. This keeps back all the solid particles and allows the liquid to run down to the true bottom. The liquid (the wort) can then be drawn off ready for the next stage. Milled slots Wear line
G a p in c r e a s e s w it h w e a r
The advantage of wedge wire over cut slots is that wear on the wire does not produce an " opening" of the gap.
Wedge wire slots Wear line
No gap change with wear
The false bottom is built up of interlocking plates. These may have either milled slots or they may be built up of wedge wire.
The plates are made in sections so that they can be lifted. This enables them to be thoroughly cleaned if required.
Sparge It has a sparging system. This is used to spray water over the mash to wash out the worts. Once the strong wort has been collected, the water spray washes out the remaining wort. Rakes It has a raking system. These are knives that can “cut” the bed. This, when used properly, helps the filtration process.
There is a CIP (Cleaning In Place) system installed. There are spray balls or jets which clean the internal surface and under the plates.
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Draw off All Lauter tuns are fitted with a special draw off device. This enables the operator run off the wort without pulling the “bed” down onto the plates. This would block the slots in the false bottom.
Operation A typical lauter tun cycle to collect 1000 hl is described below. Event Underletting This covers the false bottom. It stops the mash settling into the slots and blocking them. Filling The mash is pumped from the mashing vessel. Re-circulation Wort is recirculated through the false bottom until it is bright. First worts The strong worts are run off Second worts Weaker worts are run off. Sparge water starts to wash out the wort. Last worts The last weak runnings are collected Weak worts Weak worts are sent to drain. They may be collected and used for mashing the next brew. This saves extract. However, they must be kept hot and therefore sterile. Drain down The remaining liquid goes to drain. Grain removal Spent grains are removed Under plate flush The space under the plates is cleaned. This removes any bits of grain that may have got through the slots. If it were left it would be infected very quickly. Total
Duration 3 minutes
Volume HI 23
11 minutes 4 minutes
20
41 minutes
200
74 minutes
475
10 minutes
141
16 minutes
179
8 minutes
93
25 minutes 5 minutes
197 minutes
1000
There are other devices to “strain” the wort. The most common is the mash filter.
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The mash filter What does it consist of? It consists of alternating plates. Mash is pumped into one plate. This is hollow:
Hollow plate
Perforated support plate
Perforated support Wort outlet port
The cloths are put over the adjoining plate, which has a perforated centre area. The cloth holds the mash. The wort travels through the cloth. It goes through the perforated plate and into its hollow inside. It then feeds out through exit ports. Cloths are normally polypropylene which is easily washed. The plates are held together by a hydraulic press. Page 31 of 95
A modern mash filter: the Meura 2001
Mash in
Filter plates
Wort out
The mash filter is flushed, and then preheated with hot water. The mash is then pumped into the filter through the top channel, completely filling the filter frames. The entire transfer to the mash filter is completed in 20 to 30 minutes When the filter is full, the wort collection system is opened. The wort is drawn horizontally through the filter cloths. Sparging is started after the first wort is partially drained but before the filter cake becomes dry. After the last wort, the filter is opened automatically, plate-by-plate, and spent grains fall into a trough with a screw conveyor. Whatever system we use we should produce a “bright” (clear) wort. It should also be of a consistent “gravity” (gravity is a measure of the sugar content) This wort is then pumped to a copper where it will be boiled with hops.
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Wort boiling Why boil wort? Wort boiling stops any trace of enzyme activity. It also precipitates out undesirable protein material that has come from the mashing process. This helps to “stabilise” the beer so that it keeps longer in package. It also removes unpleasant aromas that might have come from the process. Most importantly, it extracts the bittering substances from hops. Hops give all beers their characteristic bitter taste and aroma. Equally important however is the fact that boiling sterilises the wort. There are millions of bacteria and moulds that could have survived the brewing process so far. If they were allowed to grow, they would make the beer undrinkable! It’s essential that the wort is sterile before we start to ferment it.
What does a modern copper look like? All coppers are vessels designed for boiling. Some have external heating jackets like this “asymmetric copper”
Others have a central boiling column that boils the wort and “shoots” it out through a spreader
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The most modern ones have an external boiler. The wort is pumped around and the external heater boils it.
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Hops are added to the copper, usually in stages to control the bittering and aroma properties. Nearly all breweries today use hop powder or extract (we’ll look at these in the next section) When the wort has been boiled, it has to be “filtered” or “cleared” again. Boiling precipitates lots of undesirable protein and it must be removed before we can ferment it. Virtually every brewery today uses a “Whirlpool” to do this. Only a few, very specialised breweries who still use whole hops, use other devices to filter out this protein (called trub) together with the “spent” hops. Before we go onto the whirlpool, let’s look at Hops.
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Hops What are hops? Hops are the flowers of the hop plant. They have glands in the flower (the hop cone) that contain a powder called Lupulin. This powder contains bitter substances. The glands also contain oils (called essential oils) that have a pleasant aroma. These substances also contain compounds that can suppress bacterial growth (bacteriostatic). This picture shows hops on the bine. The bine is the name for the long stalk of the hop plant.
Close up of a hop cone on the bine
Hop cones after drying
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Adding leaf hops to the copper!
Why are hops used in beer? ·
For flavour
·
For Aroma
·
To help preserve the beer.
The use of hops was discovered in the Middle Ages in Europe. For many years, “brewers” had added traditional plants to Ale to change or improve the flavour. Ale was a simple, bland drink fermented from malt. They found that hops, when added to Ale, gave a distinct and pleasant flavour. More importantly, they realised that hops also helped to preserve the beer. This is because hops contain compounds that slow down or stop bacterial growth. This is known as bacteriostatic. You should remember that in the old days no one had any idea of micro-organisms so that they did not understand why beer went sour. It was marvellous to find a plant that stopped ale going sour and made it taste good. Hops today are used mainly for their flavour and aroma. Most breweries today pasteurise their beer so that the bacteriostatic properties of hops are not important. However, in some countries dry hops are still added to beer. Dry hopping means adding dry whole hops to a cask or a tank. Dry hopping adds aroma and helps preserve the beer where it is sold in casks. Other hop compounds also affect fermentation and certain biochemical processes. However, the influence is not strong and is not a fundamental reason for hop use.
History There are records of cultivated hop gardens, associated with monasteries in France and Germany in the 8th and 9th Century, growing hops for their medicinal properties. The value of hops for flavour and preservation of beverages appears Page 37 of 95
to be recognised by the 12th century. In Bavaria, the Purity Law of 1516 outlawed traditional bittering compounds and decreed that only hops could be used to bitter beers. The use of hops spread rapidly through most of Northern Continental Europe. In the United Kingdom, it took a long time for hops to displace other traditional herbs for bittering beer. There are still records of unhopped "ales" being brewed up until the 18th century.
The brewing bit The part of the hop plant used for brewing is the flower or hop cone. The cone contains small yellow granules called lupulin glands. These glands contain resins. They also contain the essential oil of the hop. The resins are converted into the bitter substances in the beer. The essential oils give the "hoppy" character. The Hop flower or Inflorescence
Hop growing Hops (Humulus lupulus) belong to the family Cannabinaceae. Hops are found in temperate (cooler) zones of the world between latitudes 350 and 700 (see diagram below). The latitude is important as a long day with a length of 15 hours or more is needed for flowering. Their natural distribution range is in the Northern Hemisphere where they can be found growing wild in hedgerows. They are now cultivated all over the world. They are even being cultivated at the very edge of the normal growing range. In South Africa, they use lights to extend the day length.
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The hop is ·
Hardy (However a minimum of 120 frost free days are needed for flowering)
·
Climbing (it needs a physical support. In nature this would be a hedge or small tree)
·
Perennial (regrows every year),
·
A herbaceous plant (leafy rather than woody)
It is cultivated (almost) solely for the brewing industry. The plant regrows annually from the same rootstock. It produces long bines between 4 and 7 meters high (depending on variety and growing systems). These are usually supported on overhead wires in the hop gardens or hop yards. Bines grow rapidly in the spring. As days get shorter, the bines stop growing vertically. They then produce side arms that bear the flowers.
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Hops supported on wire work Hop wires being strung from the trellis.
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As the first shoots appear, they are trained around the wire.
As the plant grows it twists around the supports to hold itself upright. The plant grows steadily upwards.
At the end of the growing season, the bines are cut off for harvesting. The rootstock is left in the ground to overwinter.
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New hop plants are grown from Rhizomes. These are like extra roots, produced by a mature plant. It takes up to 3 years for a hop garden (yard) to be ready for commercial production. Hop Rhizomes/growing roots, ready for planting.
Hops on the bine
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Harvested hop field (foreground), hops in full growth (background)
Hop harvesting Once the hop cones on the bines are ripe, they are harvested. This is usually at the end of August or in September in the Northern Hemisphere. In the Southern Hemisphere, it is February or March. Traditionally hops were hand picked. Note that “picking” refers to the removal of the cone from the bine. The bine has to be cut first. The requirement for casual labour was one of major factors in determining the location of the hop gardens. Today in all countries, except China and India, machines have replaced hand picking. The bines are cut and collected from the fields. They are transported to a static hop picking machine. This strips the bines and separates the cones from the plant. Firstly, the bines have to be cut from the supports. This can be by hand
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Or by machine
Separating/Picking: The hops are separated from the debris (stones, stems, leaves, sticks etc.) through a picking machine.
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They are then loaded onto the kilns
Where they are dried
They are then baled
After collection, the fresh hops have moisture content of around 80%. They have to be dried in hot air kilns (traditionally called Oast Houses) until the moisture level has been reduced below 12% (usually to 10%). This ensures the hops can be stored in good condition
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After drying, the hops require a short period of conditioning. This gives an even distribution of moisture. They are then compressed and packed into bales. In England, these are called pockets. The dried hops can be sold “as is” or processed. Processed hops are converted into three types of product 1. Pelletised hops (the most commonly used form) Whole hops, milled and compressed. 2. Hop extracts Bitterness chemical extracted and concentrated. 3. Hop oils and essences The aroma essentials extracted and concentrated
Summary Hops have the following properties: ·
Hops provide the bitter taste in beer.
·
The hop oils provide aroma.
·
Hops modify yeast performance during fermentation.
·
Hops contribute to beer texture (mouth feel).
·
Hops have bacteriostatic properties. These protect beer against some spoilage micro organisms.
·
Hops reduce over-foaming during wort boiling.
·
Hops aid in trub formation during the boil.
·
Hops act as a filter medium when a hopback is used.
·
Hops are a foam active agent in beer.
·
Cone Hops contribute tannins that may increase resistance to staling. Tannins may also contribute to chill haze.
Let’s now move on to wort clarification.
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Wort clarification Why do we clarify wort? When wort boiling is finished, we must separate: ·
The hop debris (spent hops) and
·
The coagulated protein (normally this is called the hot break or trub) before cooling.
This break consists principally of ·
Polyphenol-protein materials (complex nitrogen containing material)
·
Insoluble salts,
·
Some hop resin materials.
·
Heavy metals such as copper and iron
·
Trapped sweet wort
Insufficient trub removal or defective trub formation can result in trub carry over into the fermentation vessel. This can cause poor yeast performance and unsatisfactory fermentation. The beer may therefore be prone to infection. It will also be difficult to filter at the bright beer filter. A persistent haze may form and the taste may be affected. Separation in the brewing process is normally carried out by sedimentation or filtration. In sedimentation solids are removed by either: ·
Natural gravity
·
Induced gravity, e.g. whirlpool
·
Mechanically generated gravitation, i.e. a centrifuge.
Types of separation system The type of separation system employed depends on the nature of the hop product used. Breweries using whole hops Where a brewery uses whole cone hops, spent hop is mixed with the trub. The solid hop material has to be separated first. There are two principal methods used: Hop Back This operates in a similar way to a lauter tun. It is a vessel with a false bottom. The hops settle to form a filter bed. This retains the wort solids and allows the clear wort to run off.
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How does it work? 4. Water is let in by the underlet pipe. This floods the false bottom. This stops the hops “jamming” into the slots and blocking them. 5. The copper is discharged through the wort main. 6. Wort sprays into the hop back from the top. It is evenly distributed by a spreader plate. 7. The hops settle onto the false bottom. 8. The wort is recirculated until it is bright 9. The clear wort is drawn off 10. The spent hops are sprayed briefly with sparge water. This washes out any trapped wort. 11. After use, the hops and trub are removed, usually by hand. 12. The vessel is cleaned. 13. Cleaning routines depend on use and scaling rate.
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Hop Strainer Wort is passed into a screw conveyor/press. The press is surrounded with a fine mesh that holds back the solids. It allows the wort to pass through. As the hops proceed up the screw, they are squeezed to recover as much of the trapped wort as possible. The hops are discharged to waste. They are ejected with compressed air, normally to a small silo. This is a relatively coarse filter. It does not retain all the wort solids. The wort may have to be pumped into a whirlpool or settling tank to complete trub removal.
How does it work? 1. The wort is fed in at the top. 2. The mesh prevents the hops from falling through. 3. The screw drives the spent hops to the top where they are ejected. 4. Wort is removed from the bottom 5. There is a level control so that the machine is kept full but not overflowing 6. At the end, a small amount of sparge is added to flush the system of wort. 7. Cleaning is as required, with CIP. Breweries using hop pellets or extracts Hop pellets or powders cannot form a filter bed. Clarification has to rely on natural or enhanced sedimentation. Settling tank It consists or a tank, usually circular. Page 49 of 95
The particles settle by gravity. Since draw off happens from the top down there is considerable time for the particles to drop.
wort run off point
wort inlet
hot wort spreader wort lev el pivotable float
wort outlet How does it work? 1. Boiled wort is allowed to stand for 20 to 60 minutes. 2. This allows natural gravity settling of the solids. The float keeps the wort outlet point in the top (and therefore clear) part of the wort. 3. The float drops with the decreasing wort level until the vessel is empty. Whirlpool The whirlpool is probably the most common wort clarification system used today. It cannot be used if whole hops are used in the brewing if the beer.
Wort in
It is a circular vessel. The wort is introduced tangentially. A tangential inlet of around 200 with an inlet velocity of 3.5 m/s generally performs satisfactorily.
This makes a force. This accelerates the trub particles towards the centre of the vessel. They form large flocs that then settle down the centre line of the vessel to form a trub cone. Stir a cup of tea and watch where the leaves end up! The clarified wort is run off from above the trub cone through a series of run off points.
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How does it work? 1. Hot wort is pumped in at an angle. 2. This “spins” the wort. 3. Separation starts and particles move to the centre and bottom. 4. After a period of time (+/- 60minutes) wort is drawn off. Draw off starts at the top. This is where the wort is clearer. 5. As the level drops, successive draw offs are opened. 6. When the vessel is empty, a light sparge may be applied to the trub cone. This must not break it up. 7. The trub is removed by spray jets in the base of the vessel. Hot Wort Centrifuge Many breweries also use centrifuges. These are nearly always decanting centrifuges. Centrifuges apply centrifugal force to solids. What is centrifugal force? An outward force on a body rotating about an axis. An example would be a playground merry-go-round. The centrifugal force tries to throw you from the ride. The intensity of the centrifugal force is larger if you turn faster.
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How does a decanter centrifuge work?
Bowl
Scroll
Wort in
Clarified wort out Sludge out Feed: The wort is fed through a fixed central pipe into the distributor located in the scroll. The product is then accelerated smoothly and passes through feed ports in the scroll to the bowl. Bowl: Separation takes place in the conical cylindrical bowl. This rotates at a preset speed. The cloudy wort rotates in the bowl and forms a concentric layer around the inside of the bowl. The solids contained in the wort are deposited against the bowl wall under the influence of centrifugal force. Scroll: The scroll rotates at a different speed to that of the bowl. It conveys the separated solids in the direction of the conical end of the scroll where they are discharged. Solids Discharge: The separated solids are discharged through openings at the conical end of the bowl. They are discharged down the outlet chute.
Wort filters The standard range of brewery filters (cloth, kieselguhr and sheet) can be used. Only a few breweries use hot wort filtration. Those that do claim advantages including: ·
Excellent bright worts
·
Even fermentations
·
Reduction in the level of maturation clarifying agents
The disadvantages include: ·
High revenue and maintenance costs
·
Powder handling (kieselguhr)
·
Effluent problems Page 52 of 95
·
Poor cleaning performance
Blockages can occur and becomes a rate- limiting step in brewhouse turn-round time. This system may be used with whole hops after hop separation or with processed hop products. It can be used in addition to other wort clarification systems to give very low trub carry over. The solid trub recovered is usually added to the spent grains where it is used as cattle food. Now that the wort is clarified, it has to be cooled. It must be cooled; otherwise it would kill the yeast when we add it to the wort.
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Wort cooling, aeration & yeast pitching Why do we cool wort? After boiling and clarification, the wort has to be cooled. This is in preparation for the addition of yeast. Yeast would be killed by high temperatures (i.e. hot wort). The temperature of fermentation is also important. Too high can produce undesirable flavours. Too low and fermentation will slow and may not complete. Wort cooling describes the process between the end of clarification and the actual collection of the wort in the fermentation vessel. If this process is not correctly managed, it can have serious consequences for the subsequent beer quality. During wort cooling it is necessary to control: ·
Microbial contamination
·
Cooling (so that variations are within tolerance range)
·
Aeration/oxygenation
·
Addition and mixing of the correct quantity of active yeast
·
Formation and separation of cold break. (Cold break is a similar material to the hot break or trub that we discussed earlier. It forms as the wort cools.)
Microbial Contamination During the Brewhouse operation the wort is kept hot and finally boiled. This means that it is sterile. Wort is an ideal growth media for yeast and a large range of bacteria. Before yeast pitching, any micro-organisms that may infect the cold wort can grow without competition. This can result in a serious infection of the wort. The infection can be quickly spread throughout the brewery. Yeast cropping will continue the spread of the infection to the next brews. It is essential that the wort lines are thoroughly clean and sterilised before use.
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Cooling Wort to fermentation temperature. One of the critical ways of controlling fermentation is through temperature. The rate of fermentation is generally faster the higher the temperature. The wort leaving the whirlpool after 30 to 60 minutes stand is generally around 950C and has to be cooled to the starting fermentation temperature. Wort is usually cooled through a plate heat exchanger, (shown below) which uses cold water (and usually a refrigerant such as Glycol) to cool the wort. They operate by passing counter flows of cold water against wort on either side of a plate. Thus, wort is collected and the water is heated. The water is collected and used as preheated water for the next brew in the mashing vessels.
The plates alternate between Wort and coolant. They are separated by gaskets around the “holes”
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In order to maximise heat extraction the flows are arranged in staggered counter flows. In other words, you might have 2 “cooling” plates for each “hot” one.
If temperatures lower than the local water supply temperature are required then a second stage trim chiller is needed. This is usually a segment at the end of the wort cooler. In this segment, chilled brine or Glycol is used to achieve the final temperature. Typical collection temperatures would be: Lagers
Between 8 and 14 0C
Ales
Between 16 and 22 0C
It is most important to periodically check the plates for leakage since the return water will be used for brewing. Check across gaskets and for pin hole leaks. An engineering dye is available for this purpose. If a glycol or I.M.S. (Industrial Methylated Spirit) coolant is used to achieve final temperature there is the possibility that the wort could be contaminated. It is always a good idea to have wort outlet pressures marginally higher than coolant inlet pressures since in this way at least the wort will not be contaminated.
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Aeration/Oxygenation & yeast growth Why do we aerate? An all-malt wort will provide: ·
All the nutrient energy (carbohydrate in the form of sugar)
·
Growth materials such as amino acids, vitamins and minerals
to support healthy yeast growth. However, wort is deficient in certain phospho-lipids necessary to form the yeast’s cell wall membrane. Yeast requires oxygen in order to synthesise the cell wall material. This is why we aerate or oxygenate the cold wort prior to yeast addition. If the yeast is unable to grow, this will result in a poor or sluggish fermentation. The sugar is not used up and a non-standard beer is produced. Pure oxygen is frequently used, particularly with high gravity brewing. Air may not provide the necessary degree of oxygen concentration to enable normal yeast growth. (Wort saturated with oxygen contains 5 times the oxygen level of normally aerated wort). It is surprisingly difficult to get oxygen to dissolve in wort (or water). Using air, only about 8 ppm oxygen can be achieved. In case higher levels of oxygen are needed, the addition of pure oxygen is required. The amount of dissolved oxygen required varies according to the yeast strain. It is also related to the Original Gravity of the beer being fermented. The required amount of dissolved oxygen is usually in the range 7 to 18 ppm. What does aeration achieve? High aeration produces: ·
High yeast growth
·
High extract loss (since yeast growth is excessive).
Low aeration produces: ·
Low yeast growth
·
Potentially poor fermentation
Where & how should we aerate? There is a difference of opinion as to when the wort should be aerated. Aeration at the "hot" end of the heat exchanger has the advantage that the air is sterilised. In addition, the passage through the heat exchanger will thoroughly dissolve the gas. However, this will result in significant colour pick up and can affect flavour by oxidation reactions. Page 57 of 95
The introduction of air into the cold wort has opposite advantages and disadvantages. In any event, the air/gas supply should pass through a dehumidifier and sterile gas filter before use. Most breweries aerate on the “cold” side. If multiple brews are added to a fermenter, the aeration of subsequent brews is frequently omitted since the yeast would be well into its growth phase. Oxygen is usually added to cold wort. Its solubility is higher, and there is less risk of wort oxidation. (Wort oxidises faster when hot: oxidation gives unpleasant flavours). Some brewers add the oxygen in the middle of the wort cooling heat exchanger when the wort is sufficiently cold. The turbulent flow conditions ensure good gas and wort mixing. Other brewers use specialist wort aerators, which inject the air (or oxygen) as very small bubbles. Huppmann Oxygenator
Oxygen in
Restriction
Decompression
Compression
Oxygen is injected through a small ring embedded in the main pipe. The wort flow is restricted. This builds up pressure. After the restriction, the bubbles rapidly decompress and dissolve.
Ensure that you only use air from an oil free compressor. In any event, the air/oxygen should pass through a sterile filter. Safety Be aware that pure oxygen can explode in contact with grease. All joints and fittings should be grease (and oil!) free if oxygen is used.
Yeast pitching Pitching means adding yeast to the cooled wort. Without yeast, we could not produce beer. The wort would not ferment. For the best result, the pitched yeast should be thoroughly mixed with the wort. In large fermentation vessels such as cylindro-conical vessels, this is best achieved by in-line dosing. In smaller vessels, the yeast can be roused or mixed in as the vessel is filled. Page 58 of 95
To obtain a consistent fermentation it is necessary to pitch a constant amount of viable (living) yeast. The brewer needs to know: ·
Number of yeast cells (cell per millilitre)
·
Viability – number of live cells – (% viable)
·
Vitality – the healthiness of the yeast cells.
·
The pitching yeast is free from microbiological contamination
Typical yeast pitching rate for a 5% w/v alcohol beer is: Lagers
Between 15 and 20 million cells per ml
Ales
Between 8 and 12 million cells per ml
(Ales ferment warmer so initial yeast growth is higher: Not so many initial cells needed)
Formation and separation of cold break. When the wort from the brewhouse cools down it immediately starts to produce a haze. This is more precipitation of protein in the wort. There may also be some carryover of trub (hot break) from wort clarification. Excessive amounts of break can cause flavour and process problems in beer: ·
Formation of “dirty” yeast heads with top cropping yeast
·
Poor fermentation performance – often associated with the trub physically binding to the yeast
·
Sulphury (cabbage) flavours in beer
·
Difficulties in clarifying and filtering the beer.
These problems are usually solved by good management of the wort boiling and clarification stage. It is important that the cold break is not carried over into the pitching yeast to be used in subsequent brews. The risk can be reduced by: ·
With top fermenting yeasts: Skim off the yeast 12 to 24 hours after pitching. This yeast should be discarded.
·
With bottom fermenting yeasts: The first part of the crop (around 3 to 8% of the total volume) should be removed and discarded before the main crop required for re-pitching is collected. This is particularly important with cylindro-conical vessels where it removes the dead yeast cells along with the settled cold break.
Poor yeast management or poor control during wort cooling can result in defective fermentations and poor quality beer. Page 59 of 95
Before we move on to fermentation, let’s look at yeast,
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Yeast Yeast is a single celled fungus. It is capable of growing anaerobically (i.e. in the absence of air). It breaks down sugars to release energy and produces carbon dioxide, alcohol and water. Yeast Cells under the microscope.
Nucleus Oil droplet
Cell wall 0.005mm Vacuole Glycogen granule The different parts of a yeast cell. The Nucleus: this is where the genetic material of the cell is stored (Chromosomes) Glycogen granules: A carbohydrate energy source. Oil droplets: a fat energy source. Vacuole: An area of the cell with high enzyme activity associated with yeast growth and cell maintenance. Page 61 of 95
Yeasts are small and their structure can only be seen under a powerful microscope. Reproduction Yeast cells normally reproduce asexually. That means that they do not “mate” with another cell. They bud off new cells from a mother cell. Bud scars occur when daughter cells separate from their parents. The larger the number of scars the greater the number of generations and the older the parent cell. There is a limit on the number of daughters a yeast cell can have and hence the age of a yeast cell.
Bud scars
It is possible to force most yeasts to reproduce sexually. This is normally done by exposing them to severe conditions. In this case, two yeast cells fuse and form spores or pellicles. These can survive poor conditions for a long time. When conditions improve, the spores germinate to form a new yeast cell. Yeasts are present everywhere. They are in the atmosphere and particularly on the surface of dead and decaying animals and plants. There are a large number of yeast species. They are adapted to a variety of environments. The particular strain, which is used in fermentation, is Saccharomyces cerevisiae.
Selecting yeast for Brewing Not all yeasts are suitable for brewing. Brewers select and maintain their own yeast strain. It contributes to the processing and specific character of each beer. Most breweries use unique strains of yeast. They often use different yeast strains for different beer brands. Each yeast strain will impart different characteristics and flavours to the beer. Some of the key characteristics that are important when selecting a yeast strain are shown below: An ideal yeast for fermentation should be able to: ·
Produce alcohol & desirable flavour compounds
·
Complete the fermentation – achieve attenuation (degree of fermentation) required Page 62 of 95
·
Produce a consistently flavoured product
·
Complete the fermentation within a set time
·
Retain viability & genetic stability during fermentation
·
Be convenient for harvesting – flocculate at the end of fermentation
·
Retain viability & vitality during storage
·
Reproduce adequately
·
Ferment the sugars supplied
Yeast metabolism (growth) Brewers Yeast needs a readily available source of nutrient to grow. This includes: ·
Carbohydrate (sugars)
·
Nitrogen (alpha amino nitrogen – selected amino acids)
·
Vitamins
·
Trace minerals particularly zinc.
All of these requirements are supplied by a good brewery wort. Usually the only addition made to brewery wort is additional Zinc. Zinc Sulphate helps yeast performance. Yeast also needs a small amount of oxygen to produce cell wall material. During the process of fermentation yeast produces: ·
Heat - respiration is a heat producing process
·
Waste products which are alcohol and CO2
·
A small amount of flavour compounds
·
More yeast cells by budding.
Let’s now move on to the fermentation process. We’ve cooled the wort, aerated it and pitched the yeast.
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Fermentation Fermentation is the part of the brewing process where the yeast converts sugars into alcohol, carbon dioxide and water. The yeast also grows and produces more yeast cells. The carbon dioxide produced can be collected and used to re-carbonate beer later in the process. There are many different types of fermenting vessel from a traditional Ale brewery Yorkshire Square You can see the yeast head bubbling over the sides.
Through even more esoteric fermenting methods such as the Burton Union system. Wort is fermented in large casks. The yeast overflows into troughs where it is collected and the beer returned to the cask.
To the most common type of fermenter today, the conical. The top of conical Fermentation Vessels
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The cone bottoms
CIP in Cooling jackets
Pressure/ vacuum relief
Yeast cooling jackets
CO2 out
Wort in
Beer out
Outdoor cylindro -conical vessels
CIP out
Yeast out
Diagram of a conical fermenter
The function of any fermenter is ·
To be a vessel to contain the fermenting wort
·
To allow CO2 to escape or be collected
·
To provide cooling to manage the fermentation.
Older vessels were rectangular, often not enclosed. They had internal pipes to carry cooling liquids. Control was simple and very variable. Improvements were made by enclosing vessels to improve sterility, combined with basic in-place cleaning systems. Ultimately the conical fermenter was developed. The advantage of the conical fermenter is primarily economic. A large volume of wort can be stored in a relatively low ground surface area. The totally enclosed design makes it easy to incorporate in place cleaning. However, enclosure also makes it necessary to incorporate pressure and vacuum relief devices. These are essential to prevent explosion or collapse. Page 65 of 95
The vessels are also stronger than rectangular vessels of the same weight or lighter than rectangular vessels of the same capacity. The shape of the vessel causes a vigorous fermentation. Fermentation is completed more quickly than in shallower rectangular vessels. CO2 emission causes strong circulation currents. This improves the growth rate of yeast. It also gives more effective cooling as the wort is pushed over the cooling surfaces. The conical fermenter is ideal for Lager yeasts that drop to the bottom during fermentation. The cone makes it easy to collect yeast. There is also a small, but significant saving in the "loss" of bittering materials by yeast adsorption with bottom settling yeasts. “Conicals “ are easy cleaned. It is also easy to extract the CO2 for collection.
Fermentation in practice The principle control objectives in fermentation are yeast counts, temperature and pressure control. Little can be done at this stage if aeration or brewhouse parameters have not been correctly met. Temperature Temperature has an effect on the metabolism of yeast (as in any organism) Simply put, the higher the temperature the faster the reactions and vice versa. However, this effect on the rate of yeast respiration has other effects, such as high ester production (too many esters can be bad for flavour) and the pattern of yeast growth. Slowing or insufficiently fermented brews can be revived by allowing a higher temperature before the end of fermentation. This may however create undesirable by-products. Deep Cooling At the end of fermentation, the beer is normally cooled. This stops any further fermentation and prevents any potential yeast autolysis. (Yeast break down) The cooling routine is critical to beer quality. Too early cooling can result in unpleasant flavours. Too late can result in yeasty off flavours from yeast breakdown. Process and progress of fermentation The progress of fermentation is measured by the fall in the value of the specific gravity using a Saccharometer. Since alcohol is lighter than wort its production results in falling gravity.
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A Saccharometer. The Saccharometer works by floating in a liquid. It measures the density of a liquid. If the liquid is strong wort then it floats with the scale at the green mark. If the liquid contains alcohol then the density starts to drop. The hydrometer will sink to, say, the red line. If the beer is even stronger (more alcohol) then the hydrometer will sink more. As temperature affects density ‘tables are available to correct for changes in temperature of the liquid.
Yeast collection Yeast collection is employed to have a supply of yeast for subsequent brews. Normally yeast will be re-used for a specified number of generations (no more than 5) Yeast is normally removed from conical fermenters by pump to a chilled holding vessel (yeast storage tank), where it is retained for repitching. Gyling is also practiced, where up to 12% of an actively fermenting brew will be directly transferred to freshly collected wort. If the crop is low it may be because the fermentation has been poor or because of low calcium or other mineral substances. Lack of these will stunt yeast growth or affect yeast flocculation.
How does yeast do it? Sugar is converted to alcohol, CO2 and energy. Glucose
N 2 Ethanol (alcohol) + 2CO2 + 2ATP (Energy)
The process is carried out by a complex enzyme reaction driven by a chemical called A.T.P. (adenosine tri phosphate) The yeast used must also be fit, healthy, and free from contamination. During the course of the fermentation, the yeast should be freely dispersed throughout the wort. At the end of fermentation, the yeast will generally settle out or flocculate (for lager), when it can be cropped for repitching. Yeast removal can be accelerated through centrifugation for lagers, ales, and stouts. Page 67 of 95
During the course of the fermentation the yeast cells grow and replicate up to two to three times. Feeding the Fermentation. As well as sugars, yeast requires nitrogen. This usually comes from the malt wort. If there is insufficient soluble nitrogen, for example when high levels of cereal or sugar adjunct are used, then additional nitrogen may be required in the form of simple ammonium salts. Yeast also requires trace minerals, vitamins and metal ions. The most common added to enhance fermentation is zinc. This forms the basis of most yeast food supplements. Phases of Yeast growth The initial phase of fermentation reveals a "lag phase" in yeast growth. This is caused by the yeast re-adjusting to its environment and beginning to absorb the nutrients ready for growth. This is followed by a rapid growth phase, starting between 6 and 12 hours after pitching. By 24 hours, the growth phase is well under way with a logarithmic growth pattern. Growth is only limited by physical parameters such as temperature and the availability of nutrients such as amino acids (F.A.N.) and by the presence of oxygen. The growth phase is followed by a fermentation phase that is limited by available sugars, free nitrogen, the increase in alcohol level and to a degree by temperature. The final stages of fermentation are slow. This is where the yeast tends to "mop up" remaining available nutrient. Other biochemical reactions start, the most important being the removal of diacetyl. (Diacetyl is an unpleasant “butterscotch” flavour produced during the vigorous, main, fermentation.
Types of fermentation There are two types of fermentation: Top and Bottom. They relate to two different strains of yeast. Top fermenting yeasts are used mainly in British style Ale or Stout fermentations. The characteristic is that during fermentation the yeast rises to the top of the fermenting vessel. This means of course that we can’t use conicals, as the yeast head has to be removed from the top of the beer.
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The excess yeast is skimmed off for storage or waste. This leaves a covering of yeast on the vessel to protect the beer from air borne microbial spoilage organisms.
With bottom fermenting yeasts (virtually all lagers) the yeast tends to drop to the bottom. This makes conicals ideal as the surplus yeast can be drawn off from the cone.
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The surplus yeast is collected and used for re-pitching into another brew.
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Maturation Why mature beer? The traditional maturation process is particularly associated with Lager beers. The word "lager" means "storage" in German. Many of the traditional German beers were “lagered” for up to 9 months. This fitted the pattern of the seasons. The beer was brewed with the new season’s malted barley and hops in the autumn, when the temperatures were mild. After fermentation, the beers were stored in cellars over the cold winter to be available, fully matured as a light, fresh drink during the hot summers. Maturation starts at the end of primary fermentation, and progresses through a number of temperature stages. The beer is initially cooled down to between 60 and 80 C. It is then gradually cooled to between 20 and -0.50 C. Reasons for storage (lagering) are to: ·
Continue a slow fermentation to remove traces of foreign gas.
·
Continue a slow fermentation to remove undesirable flavour substances.
·
Increase the CO2 saturation of the beer (conditioning).
·
Aggregate and precipitate the haze forming compounds of protein and polyphenols.
·
Clarify the beer through the settlement of yeast and suspended solids.
·
Improve flavour through slow secondary fermentation.
Today few beers enjoy the luxury of 9 months maturation. The maturation stage has been reduced to between 1 to 4 weeks for most lager beers. Some brewers reduce "lagering" times to as little as 3 days. New rapid continuous maturation systems can complete the required flavour changes within a few hours. During lagering, we try to optimise: ·
Flavour improvement and removal of unwanted taints
·
Oxygen control
·
Adjustment in carbonation
·
Beer sedimentation and clarification (usually prior to filtration)
·
Beer stabilisation
Warm maturation is followed by a period of cold conditioning. Cold conditioning helps to prepare the beer for filtration and stabilises the beer. At 0 to –20C there is little yeast activity (although lager yeast can grow very slowly at this temperature).
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How do we do it? The traditional method The traditional method is to cool the beer at the end of fermentation to around 80C. The majority of the surplus yeast is removed before transferring the beer to a warm maturation tank. During the transfer, the remaining yeast becomes re-suspended. This reinvigorates the yeast. It starts to produce a slow secondary fermentation. This takes up the unwanted flavour compounds and breaks them down. In some cases, the yeast remaining at the end of fermentation is in poor physical condition. It will not produce an effective secondary fermentation. Under these circumstances, active yeast can be added in the form of Krausen. “Krausening” involves adding actively fermenting wort to the beer in the conditioning tank. The secondary fermentation also generates more CO2. Because it is carried out at a lower temperature (which increases the solubility of CO2) and often under positive back pressure, the carbonation of the beer increases. Modern method When the main fermentation is virtually complete, the beer is kept in fermenter for a further 24 and 54 hours at the fermentation temperature. This allows the yeast still in suspension to carry out the warm conditioning before being cooled and transferred to cold conditioning. The success of this procedure relies on sufficient active yeast remaining in suspension at the end of the primary fermentation. The duration of the stand, called “Ruh”, lasts until a quality specification is met. Usually this is a diacetyl specification, and hence it is often called the “diacetyl rest”. Oxygen One of the most important things during maturation is to ensure that any traces of Oxygen (Foreign Gas) are removed from the beer. Oxygen in finished beer is very bad. It reacts with compounds in the beer to form hazes and unpleasant flavours. The very slow final fermentation from the yeast remaining in the beer does this effectively. However many other measures must be taken to reduce or eliminate oxygen. The include: ·
Flushing the maturation tank with Carbon Dioxide
·
Storing the beer under a positive CO2 top pressure
·
Using CO2 for the cover flush on centrifuges (where used)
·
Using deaerated water with dissolved oxygen levels as low as .08 gms/litre dissolved Oxygen for all beer/water chases
·
Using deaerated water with dissolved oxygen levels as low as .08 gms/litre dissolved Oxygen for blending Page 72 of 95
·
The use of large modern maturation tanks. This cuts down on surface area absorption.
·
Gentle beer movements through correctly sized pipes
·
Purging of bends and pipes and the use of double seat valves to reduce oxygen pick up
·
In-line monitoring of dissolved oxygen to identify any problems and to take immediate corrective action
Sedimentation Another important aspect of maturation is sedimentation. The longer the beer is kept in the tank, the more solids will fall to the bottom. This obviously improves the efficiency of the next stage in the process, Filtration. Sometimes there is not sufficient sedimentation (perhaps because of the yeast strain). Some brewers will then use a centrifuge before the beer is filtered. How a centrifuge works. This is an example of a self cleaning centrifuge made by Alfa Laval. Cloudy beer is pumped in at the top. The centrifuge is packed with thin plates that are spun rapidly. The solids are thrown to the outside edge. The lighter liquid is discharged (bright) from the bottom. At a preset time the bowl opens at point A. This is done very quickly. The solids are ejected through the gap and the bowl closes again before liquid is lost.
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Stabilisation These days beer has to last a long time in package. Beer haze is due to a complex of molecules of protein and polyphenols. This complex is formed during cold storage and either settles out in the storage tank or is removed during filtration. We have seen that a long cold maturation will reduce these compounds in beer. We have also seen that Oxygen (foreign gas) can be very bad for beer. Nevertheless, even when we get both these to very low levels there are still proteins and polyphenols remaining in the beer that will slowly form hazes. It is possible to treat the beer so that these reactions are slowed down. This gives the beer a good “shelf life”
What can we use? ·
We can use compounds that adsorb Polyphenols such as Polyvinylpolypyrrolidone (PVPP). (Adsorb means to hold on to something.) These materials are full of tiny holes. The adsorbed compounds are held inside these holes.)
·
Compounds that adsorb Protein such as Bentonite or Silica Gel
·
We can precipitate the protein (before filtration) with compounds like Tannic Acid.
·
Alternatively, we can break down the protein with enzymes like Papain.
Once we have removed one of the components then the reaction will not occur. Where do we add them?
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Fermenter
Maturation
Bright beer
FIlter Pre filter buffer tank
Post filter buffer tank
Kieselguhr dosing
C
B B
A Stabiliser
Point A (Before Maturation)
Point B (Before Filtration)
Point C (After Filtration)
PVPP
aa
aaa
r
Enzyme
r
aa
aaa
Tannic Acid
aaa
r
r
Silica Gel
aa
aaa
r
aUse here r Don’t use here
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Filtration Why filter beer? Matured beer, however bright, still contains some yeast and haze particles. Beer has to be clear when packaged. This is mainly because: ·
The consumer expects clear beer
·
To prevent further biological changes taking place during or after packaging due to yeast or haze particles
What is filtration? Filtration involves passing un-clarified beer through a porous medium. (Porous means it will let stuff through) Some of the solids are retained in or on the medium. The clear beer passes through. The size of the pores and the depth of the filter path determine the size and number of the particles that are retained by the filter medium. Beer contains a variety of solids. Conventional filtration can only remove the yeast and a number of bacteria. We should note that “haze” is not removed by most filters. It’s too fine. We must precipitate it into larger particles or remove it by other means before filtration (see previous chapter)
How do filters work? Every filter has a type of “membrane”. This is the area which either blocks or traps particles passing through. Membranes in conventional filtration are: ·
Tightly woven or compressed sheets of fibre Photomicrograph of a filter sheet surface. See how it is built of tightly locked fibres. Filter sheets are generally made with cellulose fibre, diatomaceous earth, perlite, and a resin for bonding. This gives dry and wet strength.
·
Beds of powder Page 76 of 95
Powder is generally different grades of Kieselguhr and/or perlite. ·
Kieselguhr is the fossil skeleton of marine or fresh water microscopic organisms. It is also called “diatomaceous earth” (DE).
·
Perlite is volcanic glass.
Both are milled to a standard size for use in filtration. Perlite is generally coarser. Photomicrograph of Perlite or volcanic powder. Used normally as 1st pre-coat or coarse feed.
Highly magnified photo of diatoms used as a process aid in filtration. Used normally as 2nd pre-coat and body feed. There are two fundamental types of filtration: ·
Surface filtration
·
Depth filtration
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Surface filtration These filters usually consist of filter sheets through which the beer has to pass. The sheets are held in place by perforated plates. (Usually called a plate and frame filter) The filter membrane “holes” are sized to stop particles passing through. Solid particles are retained in the membrane. This continues until the pores are blocked. In this system, no particles larger than the “hole” size can pass through. This is described as “absolute filtration”. As soon as all the “holes” are blocked, filtration stops.
The advantage of this filter is that you can control exactly the size of particle that is let through. For example, you could use sheets that trap yeast but not bacteria. Use a finer sheet and you will trap bacteria as well. Finer still and haze particles could be trapped. The disadvantage is that it slowly decreases in efficiency as the “holes” are blocked. Generally, the sheets also have to be destroyed after use. They cannot be regenerated. This type of filter is rarely used in breweries today, as it is expensive to run. Some breweries do still use them to give a final “polish” to the beer. Depth filtration This type of filtration relies on building up a “bed” of filter material. The filter bed material is either Kieselguhr or Perlite. The filter bed is usually supported on plates or candles. Plates or candles are perforated and allow the filtered beer through. The perforations are not big enough to let the Perlite and/or Kieselguhr through. The perforated area is known as the “septum”. The filterable particles are smaller than the bed pore size. However, because the bed is thick it is difficult for the particles to pass through. They become stuck in the channels. The filter bed is continually built up by the addition of more Kieselguhr as the beer passes through the filter. This is necessary to keep more channels available for use. The filtration rate decreases only relatively slowly during the filtration run (providing an optimum body feed is injected) The filter aid is used to build up a cake on the filter support (or septum) of the filter. The filter septum (around 50 to 80 micron) is much coarser than the particles that are to be removed. These are normally yeast and bacteria at 1 to 8 micron. So the cake does the filtering, not the filter support. The diagram refers to a candle filter:
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Precoat (coarse)
Support discs
Beer flow
Beer flow
Body fe e d (fine r)
Kieselguhr
The first pre-coat uses coarse material in the range of 20 to 40 micron to bridge across the holes in the support or septum. This coat is to form a support for the finer second coat. The finer second coat will do the actual filtration.
The second pre-coat uses finer material to form a fine depth filter bed to trap the particles. The coarser range of this material has particles in the range of 10 to 20 micron, while the very fine grades have particles in the range 2 to 10 microns.
As the unfiltered beer is run through the filter, more kieselguhr (body feed) is dosed in line. This continually increases the size of the bed and keeps the filter bed open. The filter aid used is normally the same grade as that used for the 2nd pre-coat. Dosage varies according to the quality of the feed beer, from 40 to 120 g/hl of beer filtered. Ultimately the filter beds touch each other and the filter has to be cleaned and restarted.
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What type of filter should we use? There are three styles of filter commonly used. Their relative merits depend on ·
The nature of the beer being processed
·
The product mix
·
The acceptable revenue and capital costs
The Plate and Frame Filter. This filter consists of a series of vertical plates. The plates support a filter sheet. This is used to support a bed of Kieselguhr for filtration.
Hollow plate Exit hole
Inlet hole
The Beer is fed into the frame section and flows through the filter aid and filter pad into the hollow filter plate and on to the Bright Beer Tank.
Perforated support plate
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The filter has the advantage of being robust and of relatively simple design. Advantages Filter slurry can be discharged dry Simple design – low maintenance Low beer losses because of low filter volume Good for longer runs on same quality of beer.
Disadvantages High labour requirement for washing off & changing filter pads Slow turn around time Usually requires sterilization after each run Costs in replacing filter pads Difficult to keep top of filter pads free from infection Split pads can cause filter aid to bleed into bright beer Cannot be fully automated
Candle Filter. The candle filter consists of a series of vertical mounted rods or ridged candles. These have metal rings or supports to hold the filter aid. They are housed in a vertical cylindrical vessel.
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Filter head
Division Plate
Outlet
Filter bed
Filter body
The beer flows through the kieselguhr bed, up the centre of the candles into the top cavity and on to the Bright Beer Tank. It is important that the flow ensures an even distribution of beer and filter aid across all the candles.
Support candles inlet
Sludge outlet Precoat (coarse)
The kieselguhr forms a bed on the “holes” of the candle. This is the first or “pre-coat” bed. It acts as a support for the final filter bed.
Support discs
Beer flow
Beer flow
Body fee d (finer)
Kieselguhr
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Candle: The fine “holes” are just visible.
The filter is robust with a high throughput and no moving parts. Advantages Can be fully automated – low/ negligible labour required Simple design – low maintenance High throughput - good for longer runs on same quality of beer. Filter surface area increases throughout run as powder builds up on the outside of the candles.
Disadvantages Spent filter cake is usually discharged wet – effluent costs Higher beer losses due to large volume of water/beer interface. Sensitive to pressure shocks
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Horizontal Screen Filter. Beer is fed either through the top or through the bottom. This should give an even flow of rough beer and body feed across the surfaces of all the plates. The beer flows through the filter aid and mesh into the central column and on to the Bright Beer
Leaf filter in section
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These filter screens consist of a series of fine stainless steel mesh stretched over a horizontal leaf. These are housed in a vertical cylindrical vessel. The weave of the mesh is quite coarse. This requires the use of a coarse 1st pre-coat to bridge the holes.
Beer flow
Support Screens
Diagrammatic representation of the filter screen The kieselguhr forms a bed on the “holes” of the leaf. This is the first or “precoat” bed. It acts as a support for the final filter bed. Note that the bed only forms on the top of the septum. The bottom does not have “holes”
Since the filtration surface is confined to the upper leaves, the filter cake is very stable. It can be safely held for extended periods without the risk of filter cake slippage. Cake discharge is achieved by a rapid spinning of the central filter column. This throws the filter aid to the side of the tank for dry cake discharge. Advantages
Disadvantages
Fully automated – low/ negligible direct labour required Good where shorter filter runs are required Dry cake discharge for easy disposal to land fill. Low beer loss as beer can be drained down to be collected by special scavenging plates located at the bottom of the filter vessel. Low sensitivity to pressure shocks Filter cake is stable between product runs
Rotating cake discharge system adds to maintenance costs Electrical energy is required for cake discharge. The capital cost per unit filter area is higher than in the other designs since only the upper surface of the leaves are available for filtration.
Safety There is a possibility that kieselguhr and other filtration powders may induce lung damage. All powder handling areas should be thoroughly ventilated with extractor fans. Page 85 of 95
Operators should wear masks and eye protection.
Carbonation At some stage, usually after filtration, the beer’s carbonation levels will have to be checked and if necessary adjusted. The modern brewery adjusts CO2 by injecting it in line, usually after filtration and controlling the system with an inline CO2 analyser. A typical unit is the Embra CarboCheck. The CarboCheck sensor has a silicone rubber membrane through which the dissolved CO2 permeates into a sealed, evacuated chamber. The partial pressure of the gas is then measured and displayed by the analyser / control unit as a CO2 content.
CO2 Injector
CO2 is then injected as required. The injection point is a flattened pipe. This increases absorption of the CO2 over the thin beer film produced.
Picture courtesy Canongate Technology
Another device is the Haffmans carbonator. The principle is similar.
Picture courtesy Haffmans
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Bright beer Bright beer is a storage zone between filtration and packaging. The beer has been filtered and brought into specification for packaging. In order to ensure quality, the maximum temperature and time of storage should be specified: ·
Maximum storage time in bright beer tank is usually between 24 and 72 hours depending on the specifications. Any longer runs the risk of infection developing. In addition, there is the possibility of gas pressures affecting the overall carbonation specification of the beer.
·
Maximum storage temperature is usually 30C, but may be as high as 50C.
·
Level of carbon dioxide – the solubility of carbon dioxide is inversely proportional to temperature. This means the warmer it is the more difficult it is to keep gas in solution.
·
The maximum temperature permitted at the filler bowl. Beer will often pick up 1 or 2 degrees C on transfer from bright beer tank to filling. So bright beer temperature should be at least 2 degrees cooler than the required filler bowl temperature.
·
The storage time and general microbiology of the area. Cool temperatures suppress microbiological growth.
·
Some Bright Beer tanks are jacketed as well as lagged and can therefore be temperature regulated. Others can pick up around 10C per day.
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Water There’s one ingredient in beer that we haven’t discussed. Since it makes up about 95% of the product, it’s important. Yes, water. Brewing requires a supply of good clean water. It is also used for making steam, for cleaning and in packaging. The volume of water required varies between breweries. It is generally around six times the total volume of beer produced. All water that doesn’t end up in the beer is thrown away. For example, as effluent during the generation of services, as water vapour from boiling, and in the spent grain. Different kinds of water are used in different areas: Treated brewing water Softened water Mains/untreated water Demineralised water Deaerated water
Brewing Cleaning & CIP Bottle washing Pasteurisation General cleaning e.g. floors Boiler feed water. Dilution
An example of water usage to produce 1 hl of packaged beer during the different brewing operations is shown below: Production requirements: Area: Water treatment Wort production & wort treatment CIP in wort production CIP fermentation and maturation Fermentation and maturation Filtration and bright beer tanks CIP in filtration and bright beer Bottling operations (30% of total throughput) Pasteurisation Cask and/or keg racking (70% of throughput) Carbon dioxide recovery Energy requirements: Area Steam generation including condensate recovery Cooling compressor Evaporators and Condenser Compressed air Regulation air Overall cleaning operations Volume of water required in hl per hl of beer produced
Volume hl/hl 0.40 1.50 0.40 0.20 0.10 0.20 0.20 0.30 0.10 0.70 0.10 0.10 0.10 0.30 0.20 0.10 0.50 5.50
Ref: based on Moll Brewing Science & Technology Series II Volume 2 : Published by The Institute of Brewing
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Suitability for brewing In order to be suitable for use in brewing, water must be: ·
Microbiologically pure. (bug free!)
·
Clear and colourless (turbidity and colour can be caused by suspended solids)
·
Tasteless and odourless (chlorinated water can affect beer flavour)
·
pH neutral pH 7, or slightly acidic
·
Mineral composition (different beers require specific minerals. This is discussed later.)
·
Free from heavy metal ions. (these can poison yeast and cause hazes).
Microbial standards (Bugs!) Most of the water used for brewing will be heated prior to mashing. It is therefore free from most micro organisms. However, water used for diluting worts or beer or water used for rinsing equipment may not be sterile. The brewery should sterilise this water. How? Chlorine Very effective. Should not be present in water that goes into the beer. It can produce phenolic off-taste (hospital-like smell) in the beer. Chlorinated town water supplies require treatment before use. Chlorine dioxide Chlorine dioxide functions as an oxidising agent. Oxidation kills micro organisms. It is used to treat final rinse water. Ozone This treatment has a strong oxidising effect. Oxidation kills micro organisms. Ozone treatment can cause metal corrosion. UV treatment Ultra Violet (UV) light in the wavelength of 200 to 280 nm kills micro organisms. It has no residual action. Its action is limited to where it is applied. Therefore, the water should be treated immediately before use. Sterile Filtration & Distillation Page 89 of 95
Sterile filtration, Reverse osmosis and distillation will produce a sterile product. Osmosis and distillation is discussed later. Sterile filtration through a 0.45 micron filter will produce sterile water. The micro organisms are simply filtered out. All these methods are expensive.
Removal of solids Water entering the brewery, especially from surface sources, may contain suspended solids such as soil. This material must be removed, usually by filtration through a sand bed. Some of this material is very fine (particle sizes in the range of 0.1 to 0.01 mm) and this must be chemically sedimented before filtration. Incoming water is often also aerated. This precipitates Iron and Hydrogen Sulphide.
Typical schematic of a water pre-treatment system ·
Coagulants “clump” together fine particles
·
Flocculants such Aluminium sulphate or ferric sulphate or chloride may be added to the raw water. They precipitate fine particles and colloids. They are allowed to settle out by sedimentation in a settling tank. Not all suspended particles are removed in the settling tank.
·
That is why the water is then filtered using a sand filter.
·
In the sand filter, the water goes through a layer of pure sand of uniform grain size. The suspended particles stay behind in the pores of the sand when the water flows through.
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After sand filtration, the remaining Chlorine and other pre-treatment chemicals can be removed from the water using an activated carbon filter. Active carbon filters impurities and molecules like chlorine from the water by adsorbing them. Active carbon is made from coal or coconut. It works by physical adsorption of the impurities and unwanted chemicals into its structure.
Vent raw water inlet wash water discharge Activated Carbon
steam inlet
Gravel
Wash water inlet treated water outlet
drain and condensate outlet
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Minerals & Salts It is important that the water contains the correct salts for brewing. In some cases, we can add the required salts. In some cases, we have to remove them. Let’s see what effect different salts and minerals have on beer. Calcium Calcium is responsible for the fall in pH (increased acidity) during mashing and boiling. The result of lowering mash and wort pH through the addition of Calcium has the following effects: ·
Increased wort fermentability
·
Improved extract recovery
·
Increased wort free amino and soluble nitrogen
·
Improved starch conversion
·
Reduced extraction of tannins and silica compounds
·
But poorer hop utilisation
Calcium also has other beneficial effects not directly related to acidity, namely: ·
It protects amylase (enzyme) from thermal degradation. This extends its effective activity.
·
Improves protein precipitation during the boil.
·
Limits colour formation during wort boiling.
·
Improves yeast flocculation.
·
Reduces the tendency for haze and gushing in packaged beer and beerstone production.
Magnesium The magnesium salts have a similar reaction to calcium. It provides the beer with a slightly bitter or sour flavour. This is detectable at levels above 15 ppm. Excess magnesium salts, particularly magnesium sulphate may cause flatulence and has a laxative effect in humans. Magnesium helps fermentation enzymes. Page 92 of 95
Sodium At low concentrations, Sodium gives a sweet flavour to beer. Between 75 and 150 ppm, sodium adds palate fullness. At higher concentrations (around 150 ppm) it gives a salty flavour. It is added to certain Beers to give a sour salt taste Potassium Similar to Sodium. It also gives a salty flavour but is not normally added to beer. It helps some enzymes. In high dose can have a laxative effect. Iron Iron should be absent from brewing water (no more than 0.2 to 0.5 ppm). It has a negative effect on mashing. It prevents saccharification. Iron also weakens the yeast, which leads to beers without palate fullness. Iron in packaged beer acts as a catalyst in the oxidation of polyphenols. This accelerates the production of irreversible hazes in beer. It also gives a metallic taste to beer. Somewhat enhances the foam head. Zinc Zinc at high concentration poisons yeast, BUT in small amounts (0.15 to 0.20 ppm) zinc acts as yeast nutrient. The requirement depends on which yeast strain is used. It inhibits enzyme activity and contributes to beer haze. Copper ions At high levels above 10 ppm, copper kills yeast. At lower concentrations, it acts as a catalyst for the production of irreversible hazes in beer. Carbonates & bi-carbonate Carbonate ions have the opposite effect to Calcium. Carbonate ions prevent a fall in pH.
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The increase in wort pH has an adverse effect on mash enzymes. It therefore increases extract losses. The Carbonate level of brewing liquor should be as low as possible. Chloride The Chloride ion at levels up to 300 ppm increases palate fullness. They give a more mellow flavour to a beer. Chloride improves clarification and colloidal stability. Chloride inhibits yeast flocculation. Above 500 ppm, chloride leads to slower fermentations and poor beer quality. Sulphate Sulphate ions produce drier, more bitter flavours in beers. They are also a source of unpleasant sulphur compounds that can be formed by the yeast during fermentation. The relative concentrations of chloride to sulphate affect the sweetness/bitterness balance of the beer. Nitrite & nitrate Nowadays we find more nitrates in our water supplies, because of artificial fertilisers used in agriculture. Nitrate with wild yeast and bacteria can contaminate wort or beer. This can form carcinogenic compounds (ATNC).
Water hardness. ·
Hardness is that property of water, which enables it to "collapse" soap foam.
·
Hardness causes beer stone or scale on brewing vessels.
·
Hardness causes scaling in boilers and hot water installations.
·
Hardness depends almost entirely on the calcium (Ca) and magnesium (Mg) content of the water.
The total hardness consists of Temporary hardness and Permanent hardness. ·
Temporary hardness is due to the bi-carbonate salts of calcium and magnesium.
·
Permanent hardness consists mainly of sulphate, chloride and nitrate salts of calcium and magnesium.
Boiling reduces the temporary hardness. Page 94 of 95
The hardness remaining after boiling is the permanent hardness. Temporary hardness would make the water alkaline and increase the pH throughout the brewing process. Most processes in beer production proceed better or faster in acidic condition (lower pH). This is a reason for brewers to reduce the temporary hardness. We can reduce the temporary hardness by several methods. We can also reduce the permanent hardness. However, we may not want to reduce the permanent hardness, as the Ions are useful in making beer because: ·
Calcium and Magnesium are necessary for yeast metabolism.
·
Sulphate and Chloride ions are also needed for beer flavour.
We’ve covered the various methods of removing hardness in Water in the brewing modules.
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