Exam #2 Practice Problems

#.     What is cheese? – Milk that has been curdled by acid and rennet that has had most of the water removed

#.     What is the primary role of salt in cheese? – Preservative

#.     Some enzymes used in cheesemaking hydrolyse fats and proteins during the aging process. How does this affect the final cheese? – Hydrolyzed fats and proteins usually lead to smaller molecules that contribute flavor and aroma. They can also tweak the texture.

#.     Why is it important to get chymosin (rennet) from young calves rather than adult cows? – Cows only produce chymosin while they are feeding on milk, once they’re off the milk, chymosin production drops off very quickly

#.     How was rennet “discovered? – It was a happy accident. When calf stomachs were used as waterproof bags for milk storage and transportation, the rennet curdled the milk into cheese

#.     What specific protein does chymosin (rennet) react with during cheesemaking? – Chymosin reacts with the kappa-casein proteins that coat casein micelles… This lets the “gooey” inner caseins to stick together and form a network of casein micelle chains

#.     When chymosin (rennet) reacts with protein during cheesemaking, what happens on a molecular level? – Rennet “shaves” some of the kappa-casein off the outside of the casein micelles and they stick together

#.     When acid reacts with protein during cheesemaking, what happens on a molecular level? – Acid denatures the casein proteins much more completely, allowing the individual casein protein strings to interact

#.     What are the main roles of propionibacteria in cheesemaking? – This is the hole-making bacteria

#.     Brevibacterium linens mainly contributes what to cheese? – This is the “stinky cheese” bacteria

#.     What are the properties of Penicillium roqueforti and other “blue molds” used in cheesemaking? – Can survive low oxygen, found inside the cheese, digests fats, contributes sharp/peppery flavor

#.     How are the “white molds” used in cheesemaking different from the blue molds? – Surface molds, digest proteins, make creamy texture

#.     When slowly adding heat to try and melt cheese, what component (food molecule) is affected first? Second? – Fats melt first, proteins denature next, water starts to boil/evaporate off, fat/protein start to brown/burn, things start on fire, chaos ensues

#.     In dishes that contain melted cheese, what causes “stringiness”? – Too many protein-protein interactions, lots of stirring

#.     Where is most of the fat found in eggs? - Yolks

#.     What does the color of the shell of a chicken egg tell you? – It can indicate the breed of chicken, but not much more

#.     What does amylase (an enzyme found in egg yolks) do? – We talked about this one in the food molecules section, amylase digests (hydrolyzes) amylose, that’s starch

#.     After water, what is the largest component (food molecule) of egg white? – Albumen proteins

#.     What happens on a molecular level when eggs are cooked “hard”? – Proteins denature and get all tangled up

#.     Describe the molecular changes that take place when egg whites are whipped. – Mechanical shearing/denaturing  of proteins, proteins stretch and tangle, capture air bubbles

#.     What role does cream of tartar serve in whipped egg whites? – It’s an acid, it prevents the formation of too many disulfide bonds

#.     Why are very strong interactions, like disulfide bonds, unfavorable in whipped egg whites? – Very strong interactions tend to squeeze water out and limit the ability of the protein chains to slide by each other while the meringue is forming/building

#.     How does heat affect an albumen foam (a meringue)? – Heat dehydrates the meringue, also denatures additional proteins (ovalbumen) to form more network connections, if there’s sugar present the heat will also dehydrate and form a bit of a sugar-strand network

#.     What component of an egg preparation has a very high heat capacity? - Water

#.     What component of an egg preparation is an excellent heat insulator? - Air

#.     What component of an egg preparation can melt, solidify or separate depending on temperature? - Fats

#.     What component of an egg preparation affects the structure and texture of the final dish depending upon whether it has been denatured or not? - Proteins

#.     What is “candling” and why is it done? – Shining light through an egg to see the yolk and determine the egg’s grade

#.     Describe the different grades of eggs. – AA = thicker albumen, prominent chalazae; A = less thick, weaker chalazae; B = industrial eggs, yolk swirls around inside the shell

#.     What is specific heat capacity? – The amount of heat/energy required to raise a given amount of a substance by a given temperature. Usually calories per gram-degree-Celcius

#.     If the specific heat capacity of water is 1 calorie per gram-degree-Celcius (1cal/g•°C), adding 100.0 calories of heat to 20.0g of liquid water at 17°C should {increase/decrease} the temperature to _______°C. – This should increase the temperature by 5°C to 22°C. 

(100.0calories) / (1cal/g°C) = 100 g°C

(100 g°C) / (20.0g) = 5°C.

#.     What role does the water bath play when cooking/baking a custard? – Even heating, slows down and evens out the denaturing of proteins in the custard, manages heat transfer

#.     Why is tempering important? – Tempering evens out the denaturing of proteins. If hot and cold were just dumped together all at once, some proteins would denature quickly where the solution was hot and the result would be a clumpy mixture