Egg, Milk and Cheese Lab
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University of Guelph *
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2700
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Apr 3, 2024
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UNDERSTANDING FOODS
EGG, MILK and CHEESE LABORATORY REPORT
1.
Describe function of the egg whites are performing in the Cheese soufflé (Product , Egg lab) (5 marks)
In the Cheese souffle recipe, the egg whites are used for the formation of foam to make the soufflé lighter and airier. When the egg whites are beaten, the egg white proteins become denatured and gain air bubbles which help create foam. These air bubbles are important because they attach to the surface of the denatured protein and create a network that is stabilized on the layer of foam. When the foam is heated the proteins can coagulate and a permanent foam is created in the eggs. (Course pack pg. 121)
2.
Explain why an egg white foam is created more quickly when cream of tartar is added. (4 marks)
Egg white foam is created quicker when cream of tartar is added because it is an acidic substance, which means it can create a more stable foam. Cream of tartar will be able to create a larger amount of egg white foam, that will be stiffer when it is beaten. It becomes more stable through the transfer of
H+ ions, which act as a neutralizer to the negative charges, which allows the egg white protein to denature and quickly coagulate. (Course pack pg. 111) (egg live lecture)
3.
Explain the effect of under-beating egg whites when preparing an egg white foam? (2 marks)
Under-beating eggs cause the proteins to struggle to denature due to the lack of air bubbles made from beating the egg whites. This creates a foam that is not stable or has stiff peaks which can’t hold its shape and will fall quickly. (Course pack pg. 104)
4.
What effect does milk have on the function of the eggs in the Baked Custard (Product II,
Egg Lab) (4 marks)
In the baked custard, milk affects the function of eggs in multiple different ways. The milk makes the egg proteins move further away from each other and a gel is formed creating a thinner substance than if milk weren’t to be added. When adding milk, the mixture also needs to be cooked a different way, by using higher temperatures to ensure that coagulation and denaturation happen to the eggs. (Egg live lecture)
5.
Explain what the ideal temperature is for beating whipping cream into a stable, high volume foam. (7 marks)
The best temperature to beat whipped cream to make sure it is stable and has a high volume is to make sure the bowl, along with the beater is chilled to 4 degrees Celsius or below in the refrigerator. By doing this, it ensures the fat globules in the whipped cream are solid and the whipped cream is thicker. When the whipped cream is thick, air bubbles can easily come in and create a higher volume,
which the globules of fat can attach to the surface. This will ultimately create a more stable foam. (Course pack pg. 139)
6.
a) If the Hot Cocoa (Product VII, Milk & Cheese Lab) is prepared in a pot that sits directly
on the stove, instead of using a double boiler, what will you notice when you go to clean
the pot. Explain what this is and how it formed (4 marks)
If you decide to not use the double boiler and just cook it directly on the stove, there will be denatured
proteins sitting on the bottom of the pot. Whey proteins in hot chocolate such as lactoglobulin and lactalbumin become denatured when exposed to heat, which causes them to precipitate out of colloidal dispersion. When the hot chocolate is put directly into a pot on the stove it burns the proteins, using a double boiler will make sure there is less denaturation happening. (Milk and Cheese lecture)
b) You didn’t get to drink your hot cocoa right away and when you sat down to enjoy it you notice a film / skin on the surface. Explain what caused a film / skin to form. Explain how it can be avoided. (4 marks)
A film/skin on top of the hot chocolate is due to a protein in the milk called casein. When the drink sits for a prolonged period, the casein will gather on the surface of the milk and create a film at the top of the drink. To avoid this from happening, when cooking the hot chocolate, the lid should be kept on or the top of the hot cocoa should be covered. This will make sure to minimize the exposure to air as well as prevent evaporation of the water in the hot chocolate. (Milk live lecture) 7.
After the vinegar is added to the milk-cream mixture (Step #3) when making the Homemade Ricotta Cheese (Product VI, Milk & Cheese Lab) the mixture quickly changes
in appearance. Describe and explain what is happening (8 marks)
The mixture changes in appearance due to the casein proteins that are colloidally dispersed in the milk becoming denatured. Since vinegar is an acid, it denatures the milk proteins. Usually, casein micelles repel each other, but when an acid is added and lowers the pH of the milk, those negative charges in the casein become neutralized. When acid is not present in the casein micelles, they are colloidally dispersed at a pH of 6.7, but when acid is added the pH grows closer to 4.6 or the isoelectric point. This causes the casein micelles to denature and stick together, creating unstable molecules that appear curdled. This process can happen faster if the mixture is heated. (Milk live lecture)
8.
What preventative steps are being done in the Macaroni and Cheese with Tomatoes (Product III, Milk & Cheese Lab) to prevent curdling of the cheese sauce? (3 marks)
The preventative steps that are being taken are adding the tomatoes and pasta to the cheese at the same time. Since tomatoes are acidic, they would usually denature the casein, but since a starch source is added at the same time it can thicken the water surrounding the casein and prevent it from falling out of colloidal dispersion and becoming denatured. (course pack pg. 138)
9.
Explain whether Swiss cheese can be substituted for old cheddar cheese in the Welsh Rarebit recipe (Product VI, Milk & Cheese Lab). Consider the melting and blending properties of both cheeses when answering the question. (6 marks)
In this recipe, the two cheeses can be substituted due to the many similarities they share. They both are high in fat, have medium moisture, and have a similar ripening time between 1-12 months. For the cheese to blend into the recipe well it must be able to melt and be ripened, and for the cheese to melt well, the minimum fat content must be medium as well as medium moisture. Since the two cheeses both share these properties, they can substitute for one another. (Milk and Cheese lecture)
10.
From the description of Welsh Rarebit (Product VI, Milk & Cheese Lab) given in lab you were expecting to see a smooth, homogeneous sauce on slices of toast. Instead you saw a stringy, oily mixture. Explain what happened. (5 marks)
In the lab, a stringy, oily mixture was formed because the cheese had been overheated. Over coagulation of cheese can happen when it is exposed to high or moderate heat temperature for a prolonged period. These proteins that are over coagulated, will squeeze out water and shrink which will break fat emulsion and end up with an oily and stringy texture. (Milk and cheese lecture)
TOTAL = ________ = ________
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