Food Fire & Physics Final

what changes occur in droplets due to coalescence?

Droplets combine to form even larger droplets

how much energy in joules is needed to heat a cup of water from room temp to a temperature of 93C? assume the mass of the water is 300grams the specific heat capacity of water is about 4.18J.

approximately 90,000J

Why will a cast iron pan absorb more heat and hold it longer than aluminum?

cast iron is a poor conductor of heat and much denser than aluminum

jell-o is a type of gel. what is in the continuous phase?

gelatin

what is the relationship between gelatin and collagen?

gelatin comes from collagen

inadequate or excessive salt concentration or temperatures or exposure to the air lead to what problem vegetable fermentation?

growth of undesirable microbes

a fillet of tuna is cooked in a pan. how does heat move through tuna

heat undergoes a random walk through the tuna

what is the name of the bond that forms between water molecules and its constantly being broken when water is in its liquid state?

hydrogen bond

what role does the enzyme chromatin found in rennet play in cheese production?

it allows the micelles of casein proteins to become uncharged and form a continuous meshwork

a droplet of oil with a diameter of 5cm is in water. it is whisked and broken into many smaller droplets with a diameter of 1mm. why is so much energy required in the whisking to break up the drops?

it takes energy to increase the surface area between the oil drops and the water

If you hike up a high mountain and cook a box of spaghetti at that higher elevation, you will find ...

it takes more time to cook

a suspension is composed of monodispersed spheres in water. if each sphere were to think and reduce its radius by a factor of 2, how would the volume fraction change?

it would decrease

what type of basic food molecules is collagen?

protein

which of the following foods has the largest elastic module?

rock candy

in an egg, what is the ratio of water molecules to proteins?

there are 1,000 water molecules for every protein

which bag will result in more tablespoons of salt, a 1lb bag of table salt or a 1lb bag of kosher salt? the mass of 1 tablespoon of table salt is 19 grams the mass of 1 tablespoon of kosher salt is 16 grams

there will be more tablespoons of Kosher salt

why is it easy to overcook tender meat on the grill?

to be cooked but juicy, the internal temperature of meat must be heated to within a narrow range of values. however the rate of change of the temperature can exceed 10F in a minute on a grill. thus, it only takes a minute or two to overshoot the ideal range of temperatures

how will tripling the thickness of the lasagna affect the cooking time? for example, cooking lasagna that is 6 inches which rather than 2 inches

tripling the thickness will increase the cooking time by a factor of 9

a series of complex browning reactions are the Maillard reactions. what are the Maillard reactions?

when carbs and proteins are heated together an unstable intermediate structure is formed. this structure then undergoes further changes producing hundreds of different by-products. all these by-products produce brown coloration and full, intense flavor

after whipping egg whites, you notice the volume increases by a factor of 5 from the initial volume of 1 cup to 5 cups. therefore you surmise that 4 cups of air have been incorporated into the foam. what is the volume fraction of the air in the foam?

.8

how many teaspoons of water contain 1.65x10^23 water molecules? note the molar mass of water is 18g/mol. the mass of a cup of water is 237 grams.

1 teaspoon

a gel forms when the gelatin concentration is sufficiently high. with enough gelatin molecules in the liquid, their long chains can overlap with each other to form a continuous network. at what concentration is the number of gelatin molecules sufficiently high such that a gel forms?

1%

students attempt to make homemade mayonnaise. they estimate the droplets in the mayo to have a radius of 1mm. in addition, using a reference, they estimate the surface tension to be 0.24N/m. Finally, based on the ingredients used they estimate the volume fraction of vegetable oil in the mayo to be about 80%. What is the approximate elasticity of the mayo?

10 to 100Pa

how does the size of the glass of milk compare the with the size of the water molecules in the milk?

10,000,000,000 times bigger

e.coli divide every 20 minutes. at 9am during food prep cross contamination leads to a piece of spinach with e.coli on it. how many times will it divide before it is served on a salad for lunch at 1pm?

12 times

a typical yogurt culture has a doubling time of about 30 minutes at approximately 105F. If the yogurt is held at this temperature for 4 hours and there were initially 1 million bacteria, how many bacteria are there now?

256 million

the plot below represents data collected from food being heated what would the time constant be for this temp change? (see #10 on exam 2)

90 minutes

which weighs more (has more mass) one mole of sugar molecules or one mole of water molecules?

a mole of sugar molecules

what is the difference between an atom and a molecule?

a molecule is made up of atoms

a garlic aioli is an emulsion where the oil (the dispersed phase) is suspended in the water (the continuous phase). to create a thick aioli sauce, what volume fraction of water is needed?

about .2 or 20%

a microorganism in kimchi divided 30 times over the course of fermentation. If there was just one microorganism to start with, how many are there after 30 divisions?

about 1 billion

ingredients for hersheys cup of hot chocolate for one: 2 tablespoons of sugar 2.5 teaspoons of hersheys cocoa, dash of salt, 1 cup of milk, 1/4 teaspoon vanilla.....to scale this recipe to serve 20 people, how much hershey's cocoa would you need?

about 1 cup

You are trying out spherification for the first time and want to make a ravioli with a gel thickness of 1mm. you find a website that states that the diffusion constant for the calcium ions is 4.2 x 10^-9 m^2/s. How long should you leave you pureed pea with sodium alginate in the calcium bath?

about 1 minute

nutrition facts for a package of butter are shown on the rights based on number of calories from fat shown in the lable how many grams of fat is in a single serving?

about 16 grams

the nutrition facts for a particular type of cookie are shown on the right, using this info estimate the number of calories for the entire box of cookies

about 5200 calories

what is true about gelatin?

after being denatured gelatin molecules form weak bonds with each other

in a liquid foam the dispersed phase is ________ and the continuous phase is ________.

air bubbles.....a liquid

amylose and amyloypectin are starch molecules. the shapes of these molecules have a direct effect on their ability to thicken a sauce. which is the better thickener?

amylose

what is not considered a microorganism?

an enzyme

how much energy in joules is needed to heat an empty oven from room temp to a temp of 177C? Assume the oven has an internal capacity of 80 liters, which corresponds to about 97 grams of air inside the oven. the specific heat capacity of air is about 1.007J.

approx 9,000 J

the table below shows the results of an experiment where a student measured the diffusion of H+ ions in red snapper, a firm-fleshed his often used to make ceviche. what is the diffusion coefficient of H+ ions into the fish? Calculate your answer in units of mm^2/hr.

between 0.1mm^2/hr and 1mm^2/hr

Fruit preserves are a kind of physical structure called a what?

carbohydrate

this type of protein clumps together in acid conditions and is responsible for the consistency of yogurt

casein

sauteing is a method of cooking food that uses a small amount of oil or fat in a shallow pan over relatively high heat. what mode of thermal energy transfer plays a dominant role in this cooking method?

conduction

a cup of water can be cooled by adding ice cubes. as the water becomes colder the average kinetic energy of the water molecules is.....

decreasing

proteins can unfold. this change involves breaking the bonds that maintain the molecule's folded shape and undoing its natural structure. it is important to note that this change is not a change in composition, but a change in structure. this process is called _________

denaturation

brining is the process of submerging a cut of meat in a brine solution, which is simply salt dissolved in water. the meat absorbs the extra liquid and salt, resulting in a juicer more flavorful final dish. this technique is particularly great for lean cute of meat that tend to dry out during cooking. What best describes the motion of the salt in the meat?

diffusion

both carbs and proteins have polar regions. water molecules are attracted to these regions and cluster around them. when they do this, they effectively surround the larger molecules and separate them from each other. if they do this more or less completely, so that each molecule is mostly surrounded by a cloud of water molecules then that substance has __________ in the water?

dissolved

Some common thickening agents used in cooking are xanthan gum, gelatin, pectin, alginate, egg, starch and flour. What do these molecules have in common?

each of these ingredients contains long polymers

a twizzler is stretched by pulling on both ends. when the twizzler is no longer being pulled it slowly returns to its initial length. the deformation that occurred was...

elastic

a calorie is a unit of_____

energy

a microorganism uses what type of protein to break longer molecules into smaller molecules?

enzymes

there is a particular group of proteins that are important to the cook not so much for their direct contribution to food's texture and consistency but for the way they change the other components of the food they are in. these proteins are biological catalysts that increase the rate of specific chemical reactions that would otherwise occur very slowly. these proteins are called __________

enzymes

How is fish collagen different from mammal or bird collagen?

fish collagen is less cross-linked and so it melts and dissolves at much lower temperatures

the fat globules in milk is made up of a membrane that surrounds the globules. the membrane is composed of phospholipids and proteins. because of this membrane, fat globules in milk are sensitive to _______ but can tolerate __________.

freezing.....heat

When you marinate food such as meat or tofu, how does the marinade move through the food?

from the outside toward the center

lecithin is a generic term to designate any group of yellow-brownish fatty substances occurring in animal and plant tissues composed. in class we discussed the using the lecithin in eggs as an emulsifier. why is lecithin a good emulsifier?

its molecular form as a hydrophobic end and hydrophilic end

the only carbohydrate found in any quantity in milk is....

lactose

what is the cause of lactose intolerance?

lactose intolerance is due to not enough of the enzyme lactase to break down the milk sugar lactose

substance W is a liquid at room temperature, while substance Y is a solid at room temperature. this suggests that the strength of the intermolecular forces between molecules of W is

less than the strength of the forces between molecules of Y

two liquids are poured through a funnel. liquid a takes longer to flow through the funnel than liquid b even though the same volume is poured. this info tells you what about these two liquids?

liquid a has a larger viscosity than liquid b

mayo is a type of dispersion called an emulsion. what substance makes up a majority of the dispersed phase of mayo?

oil

a substance is heated at a constant rate and undergoes a phase transformation from a solid to a liquid to a gas. the temp of the substance is measured and plotted as a function of time. at which point indicated on the horizontal axis does the substance begin to transform into a gas?

only at time t3

Orange juice has a pH of around 3, whereas black coffee has a pH of around 5. How does the number of hydrogen ions in orange juice compare with black coffee?

orange juice has 100x more hydrogen ions than black coffee.

an identical amount of peanut oil and water are heated. if the same amount of thermal energy goes into each fluid, which one is hotter?

peanut oil is hotter

pectin is a polysaccharide that play a critical role in creating the right consistency in jams. when fruit is cut up and heated near the boil, the pectin chains are shaken loose. however upon cooling, they do not re-form a gel partly because....

pectin molecules in water accumulate negative electrical charge and repel each other

________ have many different chemical environments along its chain: parts that attract water molecules, parts that avoid water molecules, and parts that are ready to form strong bonds with similar parts of similar molecules

proteins

the maillard reaction requires which two macromolecules

proteins and carbs

grilling and broiling are the modern controlled versions of the oldest culinary technique, roasting over an open fire or glowing coals. in grilling, the heat source is below the food; in broiling, above. broiling is largely a matter of what type of heat transfer?

radiation

the viscosity of ketchup changes as it starts flowing from the bottle. the phenomenon is called:

shear thinning

________ is understood to be a manifestation of starch retrogradation which is recrystallization of the starch granules as the water migrates out of the granules.

staling

unlike fats, starches dissolve in water. what can you infer about starches from this property?

starches are polar

how does a pressure cooker change the boiling point of water?

steam builds up inside, increasing the pressure and this raising the boiling point.

when water undergoes a phase transition from a gas to a liquid, a large amount of energy is released. for this reason ___________ does an especially quick job of bringing the surface of the food up to the boiling point of water

steaming

sometimes a recipe calls for cream of tartar or lemon juice to be added to egg whites at the beginning of the beating process. why?

the acid boosts the number of free-floating hydrogen ions in the egg white, which makes it harder for bonds to form between proteins that lead to the clustering of proteins and foam failure

As you knead dough, a gluten network forms, which increases the elasticity of the dough. This suggests ...

the avg spacing between the bonds of the network are decreasing

why does stretched dough creep back to its original shape?

the coiled spring like structure of individual gluten models

why does slow cooked meat, long braises, stews, and barbecues taste tender even though the muscle fibers which have been cooked for a long time are very dry and stiff?

the collagen in the connective tissue dissolves into gelatin

if a steak is overcooked it becomes tough and rigid. what is happening to the elastic modulus?

the elastic modulus of the steak is increasing

what is kinetic energy?

the energy of motion

free fat or oil can make foams unstable. why?

the free fat or oil will go to the interface between the water and air and prevent the emulsifiers from settling there and stabilizing it.

what physical property determines the temp that a material melts or boils?

the interaction energy of the molecules in the material

temperature is a measure of what molecular property of a food?

the molecules moving and colliding with each other

if the elastic modulus of a food is increasing but the interaction energy is remaining constant how must the bond density be changing?

the number of bonds are increasing.

one of the keys to good cooking is knowing how to heat the food to be the desired doneness at its center without overheating the outer regions. this is not a simple task, because different kinds of foods heat through at different rates. one of the most important variables is the thickness of the food. how long would a piece of meat that is one inch thick take to cook compared to a half-inch piece?

the one inch piece would take more than twice as long to cook

if a raw tomato puree is cooked quickly close to the boil, the result is a thicker sauce as compared to slowly letting the temp rise...why?

the pectin and cellulose enzymes are denatured and become inactive while at the same time the cell walls are disrupted by the heat. the cell wall pectin that escape into the fluid phase during the concentration heating are longer molecules and more efficient thickeners as compared with molecules that were partly broken down by the enzymes.

a potato is cooked using two different methods: method 1 and method 2. for both methods the temperature of the food follows the expression: T(t)=(Food-Texternal)e^-t/T*+Texternal however for method 1, T* is a larger value. in the kitchen, what would be the apparent difference between the two values?

the potato prepared using method 2 would cook faster

overcooked eggs become both rubbery and watery. why?

the protein network becomes overdeveloped and squeezes out the water.

Flour or cornstarch is sometimes used as a thickening agent. Which descriptions accurately depicts how flour thickens a sauce.

the starch granules absorb a great deal of water and becomes amorphous networks of starch and water intermingled

why does sugar preserve fruits?

the sugar binds up water and draws moisture out of living cells making it inhospitable to microbes

heat flux is the rate of thermal energy loss or gain. as a cup of coffee cools it loses thermal energy. what are the key factors to determine the heat flux?

the temperature difference between the coffee and the surroundings

on a candy thermometer, different temperature ranges are labeled with different types of syrups. for example, hard ball occurs at about 240F to 265F and is used to make marshmallows. Hard crack occurs between 300F to 310F and is used to make butterscotch. why does the typeof syrup depend upon temperatures?

the temperatures refer to the boiling point temp of the syrup, which depends upon the sugar concentration. as the sugar concentration increases so does the boiling point.

in the expression: T(t)=(Food-Texternal)e^-t/T*+Texternal what does T* physically represent?

the time it takes to heat the food a little past half of its final temperature

starch is often used to thicken a sauce. when starch is added to the sauce, the starch granules swell and take up more volume. how is the volume fraction of the starch granules changing during his process?

the volume fraction of the starch granules is increasing

see problem 43 on exam 1

theory d

true or false: a difference in temperature of 10C is equivalent to a difference in temp of 10 K

true

true or false: liquid foams would last longer in outer space

true

what conclusion can be drawn from the plot shown on the left? (see #18 on exam 2)

viscosity increases as volume fraction of suspended spheres increases

a simple syrup consist 1 cup of water (ab 237 grams) and 1 and 1/2 cups of sugar (about 300 grams). the molar mass of water is 18g/mol and then the molar mass of sugars is 342g/mol. will the syrup contain more sugar molecules of water molecules?

water

what critical role does yeast play in bread making?

yeast convert sugars into carbon dioxide that help to inflate dough