[caption id="attachment_176" align="aligncenter" width="368" caption="Yogurt"][/caption]
Yogurt is an important component of a healthful diet, providing lots of calcium and friendly bacteria. Many people who are lactose intolerant can tolerate yogurt, because the bacteria cultures that cause it to be tangy and thick convert the lactose into lactic acid. Yogurt can be made from milk quite easily, and from soy or other non-dairy "milks" with the addition of a thickening agent.
You'll need some equipment to make yogurt: a high quality instant-read thermometer; a good stainless steel 2-quart covered saucepan;and some means of keeping your mix warm while the culture grows--I used a heating pad for this batch. Other ways to incubate include a yogurt machine, "back of the stove" while baking, a cooler partially filled with 125° (51°C) water, a warmed thermos, etc.
To make a quart of yogurt, you'll need a quart of milk and about ¼ cup of room-temperature plain yogurt--be sure that the yogurt you use as starter has live cultures. Alternatively, you can use a freeze-dried yogurt starter. If you have a yogurt machine it will recommend a yogurt starter.
First, sterilize your equipment. Then, pour the milk into the saucepan and, using medium-low heat, slowly bring the milk to 176° (80°C), stirring frequently. Use a double boiler if you wish.
Once the milk reaches temperature. put a lid on the saucepan and remove it from the heat. Let stand 5 minutes. This process kills whatever bacteria are present.
Now, cool the milk as rapidly as possible to 115° (46°C), stirring frequently. The easiest way is to put the saucepan into a sink filled with ice water. You want to cool the milk quickly so that bacteria don't have time to colonize.
Add yogurt to the pan, stir to mix, and incubate for 4-6 hours. I wrapped the pan with a large heating pad. You'll want to keep the temperature between 98° (36.5°C) and 130° (54°C), and ideally at precisely 122° (50°C). You can incubate longer than 6 hours if you wish--the result will be thicker but also more sour.
Transfer the yogurt to sterile containers and refrigerate. It will thicken slightly over the first 24 hours. If there is a little bit of whey floating on the surface of the yogurt, stir it in.