Some good recipes.
Source: From the test labs of SomethingEdible.com
Servings: Make 2 quarts
Prep Time: 1 hourCook Time: 12 hours
Instructions: Fill up the 8 qt pot half-way with water. Put on the heat & bring to a boil. Put anything that's gonna touch dairy in the boiling water and sanitize (not sterilize) for about 10 minutes. Obviously not a good idea to submerge your whole thermometer. To sanitize the smaller pot, flip it upside-down on the lager pot so the steam does the work & you don't make a mess with some scalding water.
When everything's pretty much clean, pull all the utensils out to dry on a clean towel, flip over the 4 qt pot, pour in the milk, and place the small pot into the 8 qt pot, double boiler-style. Reduce heat to medium-high (if it's not there already) and clip your thermometer onto the pot's edge. Now, we wait; stirring every couple of minutes with your spoonula, as to make sure that the least amount of funk accumulates on the bottom of the pot. While you're waiting, Measure out your 1/2 cup of plain yogurt and (separately, please) measure the cornstarch into a 1 cup liquid measure.
When the milk reaches ~ 140F, ladle out about 4 fluid oz. into a 1 cup measure with the cornstarch already in it (put the cornstarch in after the fact & there will be lumpyness). Whisk until integrated. and then return the slurry to the rest of the milk. Continue heating & stirring & checking the temperature. While that's going on, head on over to your sink, put the stopper in the drain and line the bottom of the sink w/ ice. When the milk reaches 185F, remove the pot form the double boiler & place on the ice in the sink. Start a trickle of water to move the heat away from the pot. As the sink fills, stir the milk & stir the sink water to speed up heat dispersion. Wait! not with the same spoon! Sheesh. Keep that milk clean!
When the temperature of the milk is 113F consistently throughout, take it out of the sink. Now pitch in the yogurt you've had standing by and whisk it in until completely integrated. Preheat your oven on it's lowest setting (mine's 175F) for 2 minutes and kill the heat. Meanwhile, ladle your proto-yogurt into the sanitized yogurt containers. Lid them up (they'll be pretty full) & pop them into the oven. Turn on your oven light and walk away for 12 hours. After 12 hours carefully extract your yogurt so as not to spill and transfer to the back of the fridge for a 24-hour respite. Consume freely the next day.