Making yogurt is as simple as heating milk on the stove for a few minutes then inoculating it with a live yogurt culture. It's an overnight fermentation process similar to the one we use to make our sauerkraut. The key ingredient is the bacteria that go to work on the sugars (lactose) in the milk, lowering the pH to a more acid environment, which creates a distinctively sour flavor and also gives yogurt its keeping quality.
I consider yogurt making one of the many kitchen miracles that expose the kids in my "food appreciation" classes to the science of cooking--in this case some of the biological aspects of cooking. Having discovered the beneficial effects that microbes can have on food, humans have been making and eating yogurt for millenia.
According to food authority Harold McGee, the word "yogurt" comes from the Turkish root for "thick." Heating the milk prior to fermentation changes the structure of milk proteins, causing them to link together. All of this remained a mere curiosity to most Westerners until the 20th Century, when the Nobel Prize-winning immunologist Ilya Methnikov linked yogurt consumption to the health and longevity of certain groups in Bulgaria, Russia, France and the United States.
Now yogurt has an immediate association with healthful eating, although fat, saturated fat and cholesterol are still important considerations, as with any dairy product. Kids usually are a bit put off by the sourness of plain yogurt, but immediately warm to the idea of adding fruit to create a smoothie. Smoothies are a great way to package body-building proteins with the nutritional benefits of fresh fruit.
To make a batch of fresh yogurt at home, start with a quart of the best whole milk you can find. In a pot over moderate heat, bring the milk to 195 degrees (17 degrees below the boiling point). Use an instant-read thermometer or a candy thermometer to monitor the milk's temperature and adjust the burner as needed.
Lower the heat and continue cooking for ten minutes at 195 degrees, then remove the pot from the heat and place it in a large bowl partially filled with cold water. Again using a thermometer, bring the temperature of the milk down to 110 degrees. Now stir in 1 tablespoon plain yogurt containing active cultures. (Read the label on the yogurt container. It will say whether it contains live cultures.) Pour the milk into a warm quart jar and place the jar in a cooler with several jars or a small bucket of hot water. Close the lid on the cooler and allow the yogurt to ferment overnight, or up to 18 hours.
The reason for lowering the temperature of the milk after cooking is to create an environment in which the bacteria can thrive and multiply. The warm cooler also accelerates the fermentation process. The miracle result is a quart jar full of thick, luscious yogurt you can begin to enjoy immediately.
It seems that every family has its own way of making smoothies. Our recipe is as follows: In a blender jar, place 1 peeled banana, 2 heaping cups of cleaned and stemmed strawberries (about 1 pound), 1/2 cup plain yogurt, 1/2 cup orange juice and 1 1/2 tablespoons honey. Blend until thoroughly mixed. Then add about 1 cup ice cubes, cover and blend until completely smooth.
Even kids who don't normally eat yogurt love smoothies made with this distinctive dairy product.
Note: Children allergic to milk should not eat yogurt. However, people who are lactose intolerant may be able to enjoy yogurt, since the lactose in the milk has been consumed during the fermentation process.