Separation of Milk Particles LAB
Goal: To demonstrate that milk is made of particles suspended in water
Items Needed:
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skim milk
vinegar or citric acid
coffee filter
funnel
The skim milk can also be diluted with water for a 50/50 composition.
What to do:
1. Pour out about 50 mL of skim milk into a cup.
2. Add about 2 grams of citric acid or 10 mL of vinegar to the milk and stir.
3. Filter the mixture through the coffee filter.
Questions for conversation
What did you observe?
How do you know a separation has occurred?
Why do you believe the separation occurred?
What is happening:
The added citric acid (or almost any acid, like acetic acid found in vinegar) acts the same way as
when bacteria convert the lactose to lactic acid in the cultured dairy products. Lactic acid, or in
this case citric acid, promotes coagulation of the casein particles. These are the visible white
clumps that can be filtered out. The addition of heat actually helps promote polymerization of the
protein. The differences between the heated and the unheated particles should be larger particles
for the heated milk mixture.
Determination of Fat Content in Milk Lab
Goal: To demonstrate that the amount/concentration of fat in milk can be determined
through means other than taste.
Items Needed:
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whole milk
skim milk
half-and-half or cream
three shallow pans or bowls
food coloring
What to do:
Pour a small amount of each kind of milk into separate bowls. When the milk is steady and not
moving, add one drop of food coloring to each bowl - the bowl and milk must be perfectly still.
Watch how the color spreads.
Questions for conversation:
What appears to be happening with the food coloring?
Why do you think this is occurring?
What does this tell you about fat content in milk?
Teacher Notes
Fat content in Milk
What should be observed:
The food coloring in the skim milk should spread quickly and become faint in color. The
coloring in the cream will not spread as much or as fast as in the skim milk. The whole milk
should behave somewhere in between.
What is happening:
The food coloring is water-based and will travel and diffuse better through the aqueous (water)
medium than through the fat. So in skim milk, which has a very low fat content and is
predominantly water, the food coloring spreads rapidly, whereas in cream the food coloring will
take longer to disperse since there is less water for it to travel through.
Separation of Milk Particles
What is happening:
The added citric acid (or almost any acid, like acetic acid found in vinegar) acts the same way as
when bacteria convert the lactose to lactic acid in the cultured dairy products. Lactic acid, or in
this case citric acid, promotes coagulation of the casein particles. These are the visible white
clumps that can be filtered out. The addition of heat actually helps promote polymerization of the
protein. The differences between the heated and the unheated particles should be larger particles
for the heated milk mixture.
Labs for lesson 10 were found at
http://www.princeton.edu/~pccm/outreach/scsp/mixturesandsolutions/milk/activities.htm