Name __________________________________ Date _________________ Period ________
BOCES Science Laboratory Investigation
THE PHYSICAL AND CHEMICAL
PROPERTIES OF CHEESE
Background Information
Cheese 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.
The 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.
The casein network can also be influenced by pH
Figure 1. Schematic drawing
or heat. With a drop in pH (becoming more acidic), the
of a casein micelle.
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.
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Purpose
The 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.
Materials
PENCIL
Untreated sauté pan
Force plate
Various cheese samples
Ruler
Spring scale
Procedure
PART I – SUBJECTIVE OBSERVATIIONS
In 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.
1.
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.”
2. Eat the cheese, noting the various characteristics in the table.
3. 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.)
4. Record your observations in table 1.
Type of Cheese
Hardness
Stretchability
Springiness
Table 1. Subjective observations about various types of cheese.
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Adhesiveness
Cohesiveness
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 TESTING
In 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
1.
2.
3.
4.
5.
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:
Formula 1: % increase = (size after heating)-(original size)
x 100
(original size)
Test 2: Stretchability
1.
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.
2. Carefully remove the cheese from the pan and place it on a solid, clean surface.
3. Secure one end of the cheese to the surface with your finger, and grasp the other end
with your other hand.
4. Slowly pull the cheese at a constant rate until it breaks completely. Record the
distance that it stretched in table 2.
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Test 3: Hardness
1. Cut a piece of cheese that is 4 cm thick, 4 cm wide and 4 cm long.
2. Place the cheese on the force plate.
3. Press slowly on the cheese until it has reached one half of its original thickness; in our
case, 2 cm.
4. Record the force required to compress the cheese in table 2, and immediately go on to
test 4.
Test 4: Springiness
1. Immediately after completing test 3, observe the same piece of cheese.
2. Measure the recovery of the cheese. That is, record the height that the cheese returns
to after being compressed.
3. Record this information in table 2.
4. 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
Cheese
Original
New
Diameter Diameter
%
Increase
Distance
Force
Recovery Springiness
Stretched Required
Height
Coefficient
Table 2. Data for various industry-standard cheese tests.
Analysis
QUESTION 3: Based on your findings, which of these cheeses would be best for putting on a
pizza? Justify your answer!
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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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