A Way With
You and Your Students!
Vicki Cobb, Education World Science Editor
Teach chemistry and nutrition by making cheese in the classroom.
Setting the Scene (Background)
If you asked kids today where cottage cheese comes from, they would answer, "The dairy section of a supermarket." If you asked them what happens when milk is left out of the refrigerator for a day or so, most kids know that it will spoil. But do they know that spoiled milk is a way of preserving it for future use? That just because it is "spoiled" doesn't mean that it can't be eaten? And that the most common form of edible "spoiled" milk is cheese? The best way to teach this lesson is to make some cheese yourself in the classroom.
This activity can be done as a demonstration, or small groups of students can do it together. The most important thing is that all of your utensils be very clean. Students should wash their hands before participating.
Note: This activity must be completed over two consecutive days, so don't start on a Friday. If your cheese smells bad, or if it doesn't look like cottage cheese, do not eat it.
Allow the containers of milk to stand, unrefrigerated, for several hours -- until it is room temperature. Pour the skim milk into one large bowl and the whole milk into the other. Add 3 tablespoons of butter milk to each and stir will. Cover each bowl with plastic wrap and put the bowls in a warm place overnight.
The next day the milk will be "clabbered," or like a soft custard. If you see some clear liquid around the edges, that is "whey." The milk is now ready for the next step. If you don't see any whey collecting around the edges, wait until you do.
Make slices through the custardy milk about one inch apart. Repeat in the other direction to make a crisscross pattern so rough cubes are formed.
The next step is to further coagulate the curds and cause them to separate from the whey. That is done by very slowly heating to about 100 F (just warm to the touch). If you heat the curds too quickly, or to too high a temperature, they will become tough. The ideal would be to place the clabbered milk into the top pot of a double boiler. (Alternative: Put it into a stainless steel saucepan that fits into a larger pot.) Heat over a low flame, stirring occasionally. The heating process should take about 30 minutes. Heat until the milk is just warm to the touch. Remove the curds and whey from the heat and let cool for about 30 minutes. Meanwhile, repeat the procedure with the second batch of clabbered milk.
When the milk has cooled, skim off some whey from each batch so the kids can taste it. Then
Now for the best part!
Taste each kind of cottage cheese. Which curds are more tender? (The ones from whole milk are.) Which taste better? Salt the cheese and mix in some heavy cream (creamed cottage cheese) and eat it. Save it in the refrigerator.
Behind the ScenesA kind of bacteria, called a lactobacillus, uses milk as food. In the process it gives off a waste product called lactic acid that causes the protein in milk to clot. Buttermilk and yogurt, both cultured milk products, are a source of live lactobacilli. When you heat the clotted milk, you further change the milk protein so that more liquid is expelled. Butterfat makes the curd more tender and improves the flavor. Many hard cheeses start as cottage cheese. Their curds then are pressed together and aged. The best tasting cheeses have a high butterfat content.
Article By Vicki Cobb
Copyright © 2006 Education World