PROC-5131-05 FOOD PROCESSING 1 LABORATORY
Laboratory 3- Viscosity Measurement using a Brookfield Viscometer.
Instructor: Iraj Mehrnia
Lead Author: Jashandeep Kaur (100712807)
Partners: Erin, Nissy
Date of Lab: Thursday, September 27, 2018
Date of Submission: Sunday, October 7, 2018
The main aim of this lab is to get familiar with rheology of fluids, their viscosity measurements (Honey and Fresh salad dressing) due to shearing of spindle and changes with respect to temperature and speed effects.
This experiment is about the behaviour of several fluids (Honey and fresh salad dressing) along with the idea of viscosity measurements. It also gives the information related to the changes in viscosity with respect to the variations in temperature and speed(shear). RHEOLOGY is the study of flow of matter to investigate the response of materials to the applied stress or strain (which generally accounts of the behaviour of non-Newtonian fluids like the samples used in this experiment) and with the aid of viscosity, texture of the food can be enhanced, varied and upgraded. Lots of liquid media must be carefully pumped through pipelines. The viscosities in the food industry sector range from aqueous to pasty. The temperature-dependent viscosity plays am important role during the determination of flow of sauces, dips, mayonnaises and liquid additives for quality control. Viscosity is inversely proportional to the speed of spindle as it decreases by increasing the speed of spindle. In this lab, both temperature as well as speed variations are recorded.
The internal resistance to the flow of any kind of liquid is called VISCOSITY. The nature of different ingredients (appearance, flavour, nutrition and texture) which are used in food processing companies depend upon viscosity. Honey is more viscous than water is a good example of this. Poiseuille and Pascal second are the SI and CGS units respectively. The fundamental physical relationship between viscosity and stress can be explained by the term known as RHEOLOGY.
Isaac Newton gave this viscosity term which is now widely used in order to determine the behaviour of several liquid samples. Dependent upon the Newton name, Fluids can be classified as:
the single-coefficient of Viscosity for a specific Temperature i.e, it will change with temperature but not change with the Strain rate and shows a linear relationship between the shear stress and viscosity. For example, Alcohol.
there is change in viscosity when we apply shear.
For example, honey.
The instrument which is widely used to determine the viscosity of various food items is Brookfield Viscometer. The motor in the viscometer is responsible for the action of shearing by rotating the spindle at different revolutions per minute (rpm).
The factors which can affect the viscosity of a fluid like temperature, heat, size of particle and chemical properties of the fluid. Viscosity plays a key role in processing decisions for mixing, manufacturing and filling containers with product which is ready for sale.
Viscometers are widely being used in the food and pharmaceutical industries are using viscometer on a large scale for testing and formulating various samples like ketchups, jams, ointments.
The texture of a food and how it feels in the mouth is one of the most important selling factors, along with flavour.
S.NO MATERIALS/APPARATUS LOT#/SERIAL NO. EXPIRY
1. French salad dressing/ great value L1381A32F AUG/23/19
2. Honey/great value JN-2012707 –
3. Thermometer T64599 –
4. Brookfield Viscometer/ cole palmer VCPL 140138 –
5. Refrigerator 101525 –
APPARATUS AND MATERIALS:-
Viscometer was calibrated.
Out of 3, one beaker was filled with 200ml Honey and rest of 2 with 200ml Salad dressing. 1 out of 2 was placed in refrigerator for one hour.
2 other beakers were analysed at room temperature.
Prior to each measurement, fluid temperatures were measured and recorded as rheological properties were strongly dependent on temperature.
Viscometer model no., spindle size, product information and sample temperature were also recorded on data sheet.
Spindle was immersed in the fluid till the marked notch point on shaft putting the viscometer motor off.
Digital viscometer was put on zero if necessary.
Motor was set on lowest revolutions per minute(rpm) and % of full-scale torque reading was recorded when stable value was shown by digital display.
This step was repeated and recorded by increasing the rpm until maximum rpm or 100% full scale torque had been obtained.
Motor was stopped to raise the spindle slowly for cleaning purpose with soap and water.
These all steps were repeated for Salad dressing samples.
RESULTS AND OBSERVATIONS:-
Viscometer make and model – cole -palmer viscometer
Spindle size – L3
TABLE 1 – Salad Dressing at Room Temperature
SPINDLE SPEED % READING TEMPERATURE VISCOSITY (mPa-S)
20.0rpm 62.4% 21* C 3740.9 mPa-S
10.0rpm 49.9% 21*C 5987.7 mPa-S
TABLE 2 – Salad Dressing for Refrigerator sample
SPINDLE SPEED (rpm) % READING TEMPERATURE VISCOSITY (mPa-S)
10.0 rpm 66.0% 4.5*C 7893.6 mPa-S
6.0 rpm 55.4% 4.5*C 17245 mPa-S
5.0 rpm 53.1% 4.6*C 12744 mPa-S
4.0 rpm 49.8% 4.6*C 14944 mPa-S
TABLE 3 – Honey
SPINDLE SPEED (rpm) % READING TEMPERATURE VISCOSITY (mPa-S)
5.0 rpm 54.5% 22*C 13136 mPa-S
4.0 rpm 43.6% 22*C
The graph represents the information that by increasing the rpm speed, there is a decrease in the viscosity.
This lab experiment provides the data which shows the dependence upon the temperature and how the change in the action of stress, affects the viscosity using the samples of honey and fresh salad dressing.
Spindle speed: the maximum speed of spindle for honey sample was 5rpm,
It was 20rpm for fresh salad dressing while
10rpm for the refrigerator one.
In Case of negative value in the percentage reading, it can be due to following reasons:
The viscometer may not be levelled up accurately.
The notch of spindle should always touch the sample used.
Moreover, the changes in the values of viscometer can be occurred as the readings were taken using thermometer which was not kept under tight conditions.
This indicates the importance of viscosity of different ingredients that are mostly by the food industry.
What is viscosity?
Viscosity is the resistance of a fluid to the flow or may be defined as the magnitude of internal friction. It is expressed as ? and its unit is Pascal second.
What is a Newtonian fluid? What is a non- Newtonian fluid? Which of your materials responded as a Newtonian fluid?
Newtonian fluids are those which shows a linear relationship of viscosity with shear stress which means that the viscosity remains constant no matter how much stress is applied. Alcohol and water are the examples.
Non-Newtonian fluids depicts variations in viscosity which shear stress is applied. The graph is no longer remain linear in this case. Honey and salad dressing are the examples of this type of fluid.
NONE of the sample responded as a Newtonian fluid.
What effect does temperature have on the viscosity of fluid foods?
Due to the increase in the temperature, the Kinetic energy of the molecules also increases, which is responsible for the collisions of the molecules with one another and ultimately results into increased mobility. Hence, viscosity decreases with increase in temperature.
How may food composition impact the viscosity? What ingredient in the salad dressing may impart deviations from Newtonian behaviour?
Emulsions of oil and water are present in the food samples which are responsible for higher viscosity. The naturally present proteins, lipids and large polysaccharides also give contribution towards thickness, texture of the food and hence viscosity of the fluid.
XANTHAN gum (a polysaccharide) which is thickening agent present in salad dressing which is used to thicken the food products to improve the viscosity. In addition to this agent, oil in water type emulsions are also exist in dressing which contribute to viscosity.
XANTHAN, imparts deviations from Newtonian behaviour.
Describe the importance of viscosity in food processing, quality control, and consumer satisfaction?
Viscosity plays a crucial role in food making and processing industries as most of the food products require a certain value of viscosity such as salad dressings, honey, ketchups, jams and many more to get perfect texture, odour and flavour with the addition of stabilizers and thickeners. During processing, flow properties of liquid foods are determined and controlled to achieve the beneficial effects for consumers.
More viscous the fluid, less water content it has. So, it shows that the product will be less susceptible to bacterial decomposition which indicates better and long shelf life.
For samples at similar temperatures and identical speeds, was the viscosity of honey ever less than the viscosity of salad dressing? Is this behaviour representative of the sample rheology at all speeds?
No, as the spindle speeds taken for honey and salad dressings are different. So, it is difficult to say that viscosity of honey is less than salad dressing. Moreover, it doesn’t follow the same trend at all speeds.
Why is it important to test samples at more than 1 speed?
The testing of the sample at more than 1 speed is very important to get more specific data as well as to produce an accurate graph between viscosity and revolutions per minute(rpm).
Viscosity of Salad Dressing Lab – Pharmahub
Viscometers: The Science of Measuring Fluid Flow | Labcompare.com
Civille, G. V. Food Texture: Pleasure and Pain. Journal of Agricultural and Food Chemistry. 2011, 59, 1487-1490.
Overview of Food Ingredients, Additives ; Colors – FDA
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