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This week's LabZone activity
Nov. 26, 2003
How Can You Turn Milk into Cheese?
One of the solutes in milk is a sugar called lactose. Some people cannot digest of break down the lactose. As a result the lactose remains in their digestive tract where it can cause cramps, bloating, and diarrhea. To avoid these problems, people with this condition must drink lactose-free milk. Unlike regular milk, lactose-free milk will never turn sour. Given enough time, the lactose in regular milk turns into another chemical called lactic acid, which has a sour taste.
You can always tell if milk is sour by tasting it. But you really do not want to do that. Fortunately there is a more pleasant way. Just look for clumps in the milk. These clumps are all the particles, including lactic acid, that come together when milk sours. Both cheese and cream cheese are made by first clumping all the particles in milk. Here is how to make your own cheese.
Materials:
- buttermilk
- regular milk
- small pot
- stove
- an adult
- large plastic container
- spoon
- measuring cup
- thermometer
- cheesecloth
- rennin tablet
Method:
Add about 1 fluid ounce of buttermilk to about 200 fluid ounces of regular milk in a plastic container. Stir to mix the buttermilk and the milk. The buttermilk contains a chemical that will cause the lactose to turn into lactic acid rather quickly. But it does take some time, so allow the container to stand for at least four hours. While you are waiting, you can use the leftover buttermilk to make pancakes.
Pour the milk sample into a pot. Under adult supervision, gently warm the milk to around 30°C. While stirring, add a crushed rennin tablet to the milk. Rennin is sold in supermarkets under the trade name Junket. Slowly increase the temperature of the milk to 38°C. Do not allow the temperature to go above 38°C. Continue stirring and heating for several minutes.
Examine the contents of your pot. If you wish, you can collect the clumped particles (your cheese!) by filtering the contents of the pot through cheesecloth. Can you guess how cheesecloth got its name? Allow the solids to dry. The solids are known as the curd, and the liquid that passed through the cheesecloth is called the whey. Add some salt and taste your cheese. Unfortunately, it will not taste anything like the cheese you find at the supermarket. Commercial cheese is prepared in a more elaborate manner and is slowly aged to give it flavor and texture. Do not try aging yours because it will probably spoil. Cheese makers add chemicals to prevent spoiling.
Project Idea: Turning Milk into Glue
Adding vinegar to milk and then heating it produces a gluelike substance. Pour 125 ml of nonfat milk and 25 ml of vinegar into a small pot. Under adult supervision, heat the mixture gently while stirring continuously until small lumps begin to form. Remove the pot from the stove and continue to stir until no more lumps form. Allow the lumps to settle and then filter the mixture through cheesecloth to collect the curds. Return the solid to the pot. Add 30 ml of water to the solid and stir. Add 1/2 teaspoon of baking soda. Observe what happens. Continue to add a little more baking soda until no more bubbles appear. Scrape out the solid material from the pot and test its adhesive properties.
Try to develop the most adhesive glue by varying the proportions of the ingredients. Compare the properties of your product with commercial glues. You can test their adhesive properties on paper, wood, and metal objects. If your product glues two things together, how long does it work compared with commercial products? Check the Internet to learn more about the chemistry of glue making.
Reprinted with permission from Science Fair Success Using Supermarket Products by Salvatore Tocci. Text © 2001 by Enslow Publishers (www.enslow.com).
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