TITLE: Experiment 6 – Measurement of Viscosity in Foods by Means of Brookfield Viscometer INTRODUCTION: Viscosity is the measure of the internal friction of a fluid. This friction becomes apparent when a layer of fluid is made to move in relation to another layer. The greater the friction, the greater the amount of force required to cause this movement, which is called shear. Shearing occurs whenever the fluid is physically moved or distributed, as in pouring, spreading, spraying, mixing, etc. Highly viscous fluids, therefore, require more force to move than less viscous materials. Viscosity is a very important factor in the food industry. For example, in the chocolate making industry, the viscosity of the chocolate must be perfect for highly efficient, cost effective production. The melted chocolate must flow fast enough through the pipes so time isn’t wasted when it is transported to different areas of the factory, but simultaneously it should be viscous enough to keep its structure when placed in different moulds and when coating fillings evenly during the enrobing process. Also, the time it will take to set (or dry) the end products, all depends on the viscosity of the chocolate. Dispensing the fluids into packaging is also viscosity dependant as this process also needs to be quick to save time and money. A viscometer is a device made for the detection of robustness, also called viscosity, of different liquids. A viscometer is mostly used in laboratories and process regulation and control. To detect viscosity there are several types of viscometer. The viscometer is diverse in its functional principle. Today, there is a large viscometer range on the market in several designs and for several demands. There is a standard viscometer for 1-point measurement. This viscometer is portable and made for stationary use as well as for measurements that depend on a fixed place. A stationary viscometer is a complex measuring system that requires a detailed determination of liquids. Usually viscosity is associated with viscosity in shearing. Another possibility is to measure viscosity with the help of extensional viscosity. For instance, the flexible mobile viscometer PCE RVI 3 is suitable particularly for a quick investigation of the viscosity of different liquids. The mobile viscometer determines the viscosity based on the widespread and in many companies established as a standard measurement method Brookfield
method. Besides that, viscometer PCE RV1 1 is the analogue rotational viscometer immediately gives the user quick information on the viscosity of certain test material during production control. In the other hand, the hand viscosity meter viscolite allows practitioners in a company an absolute mobile measuring of the viscosity - as a measuring device for multi local application. Viscosity measurements are used in the food industry to maximize production efficiency and cost effectiveness. It affects the rate at which a product travels through a pipe, how long it takes to set or dry, and the time it takes to dispense the fluid into packaging. The production process has to be designed with the viscosity of the product in mind, making sure that pipes are angled to optimize flow, or that dispensers provide the right amount of force to induce flow, but not so much that the packaging will overfill. Viscosity is also a characteristic of the texture of food. The product’s viscosity must be measured and monitored during production to ensure that each batch is consistent and will go through the production process efficiently
OBJECTIVES: 1. To measure the viscosity in foods by means of Brookfield Viscometer 2. To study the effect of rotational speed on viscosity 3. To study the comparison of viscosities between two samples
RESULTS:
Table 6.1.1: Spindle Number 3 (Yogurt) Rotational Speed (rpm) 1 2.5 5 10 20 50 100
Viscosity Reading (mPas) 14730 3670 2170 1610 1110 710 510
Graph of Viscosity Versus Rotational Speed For Yogurt 16000 14000 12000 10000
Viscosity Reading
8000 6000 4000 2000 0
1
2.5
5
10
20
50
Rotational Speed (rpm)
Table 6.1.2: Spindle Number 3 (Tomato Ketchup) Rotational Speed (rpm) Giant
Viscosity Reading (mPas) Kimball
100
1 2.5 5 10 20 50 100
18080 9190 5530 3380 2080 1110 710
7780 4170 2620 1620 1040 595 395
Graph of Viscosity Versus Rotational Speed for Both Sauces 20000 18000 16000 14000 12000 Brand Giant
Viscosity Reading 10000
Brand Kimball
8000 6000 4000 2000 0
1
2.5
5
10
20
50
100
Rotational Speed (rpm)
Table 6.2.1: With Any Suitable Speed (Yogurt) Rotational Speed (rpm) 100 100 100
Spindle Number 2 3 4
Viscosity Reading (mPas) Error 510 410
Graph of Viscosity Versus Spindle Number For Yogurt 600 500 400
Viscosity Reading 300 200 100 0
2
3
4
Spindle Number
Table 6.2.2: With Any Suitable Speed (Tomato Ketchup) Rotational speed
Spindle Number
(rpm) 100
2
Viscosity Reading (mPas) Giant Kimball Error
Error
100 100 100 100 100
3 4 5 6 7
710 710 700 600 0
380 410 370 0 0
Graph of Viscosity Versus Spindle Number For Both Sauces 800 700 600 500 Brand Giant
Viscosity Reading 400
Brand Kimball
300 200 100 0
2
3
4
5
6
7
Spindle Number
DISCUSSION: Viscosity is a principal parameter when any flow measurements of fluids, such as liquids, semi-solids, gases and even solids are made. Brookfield deals with liquids and semi-solids. Viscosity measurements are made in conjunction with product quality and efficiency. Anyone involved with flow characterization, in research or development, quality control or fluid transfer, at one time or another gets involved with some type of viscosity measurement.
In this practical, we had used Brookfield Viscometer to measure the viscosity in foods. There are two type of food that had been determined which are yogurt and tomato ketchup. Both samples are non-Newtonian fluid. A non-Newtonian fluid is a fluid whose flow properties differ in any way from those of Newtonian fluids. Most commonly the viscosity of non-Newtonian fluids is not independent of shear rate or shear rate history. However, there are some nonNewtonian fluids with shear-independent viscosity that nonetheless exhibit normal stressdifferences or other non-Newtonian behavior. Many polymer solutions and molten polymers are non-Newtonian fluids, as are many commonly found substances such as ketchup, custard, toothpaste, starch suspensions, paint, blood, and shampoo. In a Newtonian fluid, the relation between the shear stress and the shear rate is linear, passing through the origin, the constant of proportionality being the coefficient of viscosity. In a non-Newtonian fluid, the relation between the shear stress and the shear rate is different, and can even be time-dependent. Therefore a constant coefficient of viscosity cannot be defined. Usually, a viscometer measures the torque required to rotate a spindle in a fluid. The spindle is driven by a synchronous motor through a calibrated spring and the deflection of the spring is displayed by the viscometer. By changing speeds and spindles, a variety of viscosity ranges can be measured. On the first activity, we had compared the viscosities of the two samples by using spindle number 3 at different rotational speeds which are 1, 2.5, 5, 10, 20, 50 and 100 rpm respectively. This rotational measurements fall into stress-controlled category. In stress-controlled measurements, a constant torque is applied to the measuring tool in order to generate rotation, and the resulting rotation speed is then determined. If well-defined tool geometry is used, the rotation speed can be converted into a corresponding shear rate. From the result obtained, we had plotted a graph of viscosity versus speed for both samples. Viscosity is plotted along the y-axis and speed (RPM) along the x-axis. The slope and shape of the curve indicate the type and degree of flow behavior. By referring to the graph, it can be conclude that as the speed increases, the viscosity reading decreases. This is falls under pseudoplastic type of non-Newtonian flow behavior. The fluid displays a decreasing viscosity with an increasing shear rate. This type of behavior is called shear-thinning. On the second activity, we had determined the effect of spindle size (ie. Spindle number) on the viscosity of the samples. The spindle number had been used are 2, 3, 4, 5, 6, and 7. From
the result obtained, we had plotted a graph of viscosity versus spindle number for both samples. As for yogurt sample, the viscosity reading decrease as the number of spindle increase. Same goes with tomato ketchup. This is because both the yogurt and tomato ketchup are shear thinning fluids. The viscosity decreases with increased shear rate. There are various precaution steps that should be considered while using the Brookfield Viscometer. For instance, make sure the spindle is tightened securely to the viscometer coupling. Besides that, check the straightness of all other spindles and replace if bent. If inaccurate readings occurred, verify the spindle, speed and model selection. Then, if percentage readings are under-range (less than 10%), the display will flash; change spindle and/or speed.
STUDY QUESTIONS: 1. Name two other product beside your samples that are of low, medium and high viscosity. The example for low viscosity product is water and oil. As for the medium viscosity, the example of product is sugar syrup while example for high viscosity is mayonnaise. 2. Name other types of equipment used to measure viscosity in foods. The other type of equipment used to measure viscosity in foods is rheometer.
CONCLUSION: By referring to the graph of viscosity versus speed for both samples, it can be concluded that as the rotational speed increases the viscosity reading decreases. Besides that, from the graph of viscosity versus spindle number, the result also showed that the viscosity reading decreases as the number of spindle increases. This is because, both samples are non-Newtonian and they are shear thinning fluids (pseudoplastic).
In short, we had measured the viscosity in foods. Besides that, we also had studied the effect of rotational speed on viscosity and the comparison of viscosities between two samples as well. Thus, the objectives are achieved.
REFERENCES: 1. Viscosity in food production. Retrieved on 22nd February 2014 from, http://www.coursework.biz/Essays/GCSE/Chemistry/446/ 2. Viscometer. Retrieved on 22nd February 2014 from, http://www.pce-instruments.com/english/measuring-instruments/installationtester/viscometer-kat_151782_1.htm 3. Rheology is a study of the change in form and flow of matter, embracing elasticity, viscosity, and plasticity. Retrieved on 22nd February 2014 from, http://people.sju.edu/~phabdas/physics/rheo.html
