This week for Biology, we made yogurt using a bacterial process. The bacteria ferments the yogurt by converting milk sugar to lactic acid. We used store-bought yogurt as starter to introduce the bacteria into the milk. The milk is heated to kill off bad bacteria and to alter the proteins to give it a better consistency.
There isn't much to do for this experiment so the instructions are in the photo captions.
Source: New York Times. You can also read more about the biology of yogurt making here.
The Ingredients: All you need is some yogurt, milk, a closed container, something to keep it warm, and a candy thermometer.
Put 3 1/2 cups of milk in a pan and heat.
The milk's temperature being tested. You want it to go up to 180 degrees.
Then put the pan inside a larger pan filled with cold water. Cool the milk down to 120 degrees.
The yogurt being poured into the container -- a quart-sized travel mug.
You want to mix in about about 2 tablespoons of yogurt to one quart or less milk.
Keep the container warm for about 12 hours. We put ours in an insulated lunch cooler.
When it's done, put it in the refrigerator. Homemade yogurt will keep for one week. Enjoy!