I've made yogurt at home quite a few times, with varying equipment and varying results. I hope that someday soon I will have an electric yogurt maker to help ease the process. But, in the meantime, I'll share my method with you, just in case you're in a similar situation...
A friend of mine recently came into a ridiculous amount of raw milk. She gets more every week than she can use, so I am the lucky recipient of the overflow... I mean, it's real milk, from a real cow. Not from a factory, from a cow and it's only a few hours old by the time it makes it's way into my kitchen. How awesome is that? Not that I grew up on a farm or anything, but it tastes the way milk used to taste (you know, that one time we took a field trip and I got to milk a cow). It's not homogenized, which means I can skim the cream off the top, and it's not pasteurized, which means I can make some awesome cheese with it.
For those unfamiliar with the pasteurization and homogenization of milk, the homogenization alters the state of the milk so that the fat particles cannot separate from the rest of the product so you always have an even percentage of fat, from the first glass to the last. Pasteurization sterilizes the milk at a very low temperature, to make it "safe" to use, but wonder of wonders, both of these processes just happen to increase the shelf life of milk to disturbing lengths. Out-of-the-cow milk tastes funny and gets chunky after about a week. Yum!
So, anyway, back to the topic at hand...
yield: 1 quart
4 c milk of your choice
1 T honey (optional)
1/3 c yogurt (either left over from your last homemade batch, or from plain store bought)
1-2 T powdered milk
Heat the milk and honey, if using, over medium heat to180F, and keep at this temperature for about five minutes. This helps the proteins set later in the process and also kills any errant bacteria. Cool in an ice bath to 115F. Add the yogurt and the powdered milk. The powdered milk helps the yogurt set to a firmer texture. Pour this mixture into a sterile container; I use a mason jar, but if you have a nice crock that would be even better.
Create a water bath in a large stockpot on your stove. Bring the water to 115F. Place a towel or potholder in the bottom of the pot, turn off the heat, and place your yogurt in the bath, being careful that the water comes at most 3/4 of the way up the vessel. You don't want any water getting in the yogurt. Cover the stockpot - if the container holding the yogurt is too tall, invert a large bowl over the pot. Using boiling water, adjust the water temperature to keep it at 115F for 6-8 hours (could take as long as 12 hours, so start in the morning). Try not to disturb the container for the full time. And that's all there is to it.