Yogurt is one of those things that if you like to eat it, you should make it. It's cheaper, tastier, and EASY! My absolutely favorite combination of circumstances.
There are, of course, a ton of different ways to make yogurt. At it's core, preparation is simply heating the milk to kill pathogens, and then adding an active bacterial culture before giving it a warm place to set up and turn into yogurt. This is the best way I've found to make yogurt, I hope you'll try it!
I like whole milk yogurt best, but feel free to use a different milk if you'd like. It won't be as rich, though. I've tried a few different ways of keeping the yogurt warm- this has been the best way, and kept the temperature up. That means the yogurt sets up faster, and makes a sweeter final product.
Finally, if you want to make this into "greek" style yogurt, once the yogurt has set, dump it into a cloth-lined colander to drain for a bit in the fridge. If you let it drain for a LONG time, you'll get something close to cream cheese (which is absolutely amazing spread on french toast and topped with jam.) Drain until it reaches the consistency you want! You can save the whey that drains out for baking with.
Ingredients and Tools:
half gallon whole milk
8 ounces plain yogurt, at room temperature (must be labeled "with live active cultures")
1/2 cup sugar
1 tsp vanilla
2 quart-size jars with screw-on lids, VERY clean
candy or milk thermometer
small ice chest
In the large pot over medium low heat, heat milk to 185 degrees to kill any possible bacteria. Stir occasionally to distribute heat in the liquid, and keep from scorching on the bottom.
Remove from heat and let cool to 105-120 degrees Farenheit. You can leave it in the pot, or put it in an ice water bath to speed things up. When it's cooled, stir in the sugar, vanilla, and room-temperature yogurt. Stir it enough to get all the lumps of yogurt out, but don't beat it to a froth!
Pour the mixture into the very clean jars (mason is fine, or old peanut butter jars), screw the lids on tight, and put the jars in the cooler. Fill the cooler to cover the jars, shut the lid, and check it in about 4 hours. If the yogurt is set when you tilt the jar, it's done! Put it in the fridge and enjoy.