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Name __________________________________ Date _________________ Period ________BOCES Science Laboratory Investigation4610100631825THE PHYSICAL AND CHEMICAL PROPERTIES OF CHEESEBackground InformationCheese is, perhaps, one of the most versatile foods around. It can be melted, sculpted, grated, chopped, fried, baked and mixed into any number of recipes. An understanding of how cheese is made, and what differences there are between various types of cheese can be instrumental in ensuring that you use this wonderful food in the best ways possible.It’s first important to know the main constituents of cheese. Cheese is made commonly made from the milk of cows, goats, sheep and buffalo; though it can theoretically be produced from any milk. Less common types of milks used in cheese making are yak, camel and horse. The milk contains mainly water, fats, carbohydrates, proteins, phosphorus and calcium, and knowing how all these come together can help us understand how cheese is made.3512185548640The primary item that merits discussion for our purposes is protein. The most common protein in cheese is casein, which can make up a vast majority of the protein in cheese depending on the type of milk used. Casein molecules form into small bubbles called micelles, and these bubbles interact with each other to form a network that gives the cheese strength. In the center of these micelles we find fat. The more fat, the larger the micelles become, and the farther apart the casein gets. So as a general rule, cheeses that are higher in fat have casein molecules that are farther apart from each other, and thus the network is weaker and yields a softer cheese. Figure 1. Schematic drawing of a casein micelle.The casein network can also be influenced by pH or heat. With a drop in pH (becoming more acidic), the casein network becomes more tightly bound together. If the pH drops too low, however, the network can break apart and form large clumps. These large clumps don’t interact with each other very well, and so the cheese may become brittle and not stretch as well. Heating cheese obviously causes it to melt and flow, because heat releases the fat from inside the micelles. This can easily be seen by melting cheese and observing that fat comes to the surface. When fat leaves the micelles, they constrict and flow more freely which we see as stretching, delicious and melty cheese. The amount of fat as well as the pH of the cheese can influence how it stretches and melts. Although there are many other constituents of cheese, and even other atoms like calcium and phosphate that participate in creating the texture of cheese, we’ll restrict our discussion to the protein casein.PurposeThe purpose of this investigation is to allow you to become familiar with some of the basic chemistry principles behind cheese and cheese making, as well as some of the common tests that are used to determine cheese quality. You’ll be able to use this information to select cheeses that have the characteristics that you desire for a particular recipe. MaterialsPENCILVarious cheese samplesUntreated sauté panRulerForce plateSpring scaleProcedurePART I – SUBJECTIVE OBSERVATIIONSIn this section, you will do something decidedly unscientific: taste your cheese samples and write down your own impressions. Because everyone chews differently, has a different amount of saliva in their mouths or likes different types of cheeses, this data won’t tell us much if we group it as a class. Individually, however, it can give you a good idea of how your observations match up with industry-standard tests and grading techniques. Obtain a small sample of one type of cheese. Write the name of the cheese in table 1 in the column labeled “Type of Cheese.”Eat the cheese, noting the various characteristics in the table.Rate the characteristics on a scale of 1-10, with 1 being low (as in low hardness – soft, low stretch – crumbly, low springiness , etc.) and 10 being high (as in high hardness – hard, high stretch – stringy, high springiness, etc.)Record your observations in table 1.Type of CheeseHardnessStretchabilitySpringinessAdhesivenessCohesivenessTable 1. Subjective observations about various types of cheese.QUESTION 1: Which cheeses did you find to have the highest stretchability? Can you find any similarities between these two cheeses?QUESTION 2: Which cheeses had very low cohesiveness; that is, which cheeses didn’t stay together very well? Did these same cheeses have low adhesiveness (sticking to other things, like the hard palate of your mouth), too? PART II – INDUSTRY-STANDARD TESTINGIn this section, you’ll perform four tests that are commonly used to grade and describe cheese. To make sure that you get consistent results, make sure you follow the procedure exactly the same for each sample that you test.Test 1: Flowability Cut a disc of cheese that is 1 cm thick. Measure the diameter of the disc and record it in table 2. Place a sauté pan on a medium-low flame until it reaches a constant temperature of 280 °C.Place the disc of cheese on the pan, and allow it to heat for 4 minutes.At the end of four minutes, measure the diameter of the disc and enter this data in table 2.Calculate the percentage increase in the size of the disc. Use formula 1 from below:x 100Formula 1: % increase = (size after heating)-(original size) (original size)Test 2: Stretchability Cut a piece of cheese that is 1 cm thick, 10 cm long and 3 cm wide. Heat the cheese on a pan for 1 minute or just until it begins to soften. Carefully remove the cheese from the pan and place it on a solid, clean surface.Secure one end of the cheese to the surface with your finger, and grasp the other end with your other hand.Slowly pull the cheese at a constant rate until it breaks completely. Record the distance that it stretched in table 2.Test 3: Hardness Cut a piece of cheese that is 4 cm thick, 4 cm wide and 4 cm long. Place the cheese on the force plate.Press slowly on the cheese until it has reached one half of its original thickness; in our case, 2 cm. Record the force required to compress the cheese in table 2, and immediately go on to test 4.Test 4: Springiness Immediately after completing test 3, observe the same piece of cheese.Measure the recovery of the cheese. That is, record the height that the cheese returns to after being compressed.Record this information in table 2.Calculate the springiness coefficient by using formula 2 below and record your result in table 2:Formula 2: Springiness Coefficient = (recovery height)/(original height)Type of CheeseOriginal DiameterNew Diameter% IncreaseDistance StretchedForce RequiredRecovery HeightSpringiness CoefficientTable 2. Data for various industry-standard cheese tests. AnalysisQUESTION 3: Based on your findings, which of these cheeses would be best for putting on a pizza? Justify your answer!QUESTION 4: Were your subjective observations of the cheeses in part I similar to the tests that were performed in part II? Explain why or why not.QUESTION 5: In terms of the composition and chemistry of cheese, why do you think some cheeses were stretchier or melted more easily than other cheeses?QUESTION 6: Many foods that we call “cheese” really bear little resemblance to actual cheese. Some “cheeses” come neatly sandwiched between pieces of plastic; others come flying out of a can faster than cheese was ever meant to move. Still others, when mixed with a little milk and butter, make delicious (if unnaturally yellow) macaroni and cheese. What modifications or changes to “real” cheese do you think must be made in order to achieve these marvels of modern culinary technology? QUESTION 7: What are some other factors that might affect how a cheese performs in these tests? (hint: think about how cheese is made, stored, aged, preserved, flavored, etc.)QUESTION 8: It turns out that some cheeses are made using enzymes or bacteria that feed on certain components of the cheese during the process of cheese making. We know that some people are unable to digest the sugar lactose, which is present in milk. Given this information, why can some people who cannot drink milk can eat certain types of cheeses quite easily?QUESTION 9: What are two things that you would change about this lab if you could? ................
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