You will need:
1 gallon of milk (hope you guessed that by now...)
1/2 cup of store-bought yogurt, to use as starter (It can be vanilla, or plain...either works.)
Then remove from the heat and either cool it in the sink with cold water around it, or just let it sit on the counter till it's down to 110 degrees.
If you resisted the urge to stir it while it was heating and cooling, (gracious, I sound like I work for a furnace and air conditioning company!) you will have a layer of cream on top.
Well, if you use fresh milk.
Not so sure if this is the case with store-bought.
Once all blended, pour the milk into 4 quart jars and put lids on them.
Some people wrap the jars in a towel and put them in a cooler.
Some folks put the jars in the oven and just keep the oven light on.
I used to set my jars in the oven and heat it to the lowest temperature possible, till the light goes off or it beeped at me. Then I'd turn the heat off and let the jars sit there. But, sometimes I'd need to bake something while they were in there, and that creates a problem. I didn't want my yogurt cooked!
Now though, (and I'm not sure if this is best way, but it's what I do,) I fill the cooler with HOT water up to the jars neck, and let the jars incubate in the warm cooler.
So, however you want to do it is fine.
The point is to keep the yogurt at a consistent warm temperature (about 90 degrees) for 9-12 hours. Mine usually gets left in a LOT longer than that...more like overnight plus some.
I don't remember right now if it gets stronger tasting the longer you let it incubate, or the shorter. *I'm a little vague on that right now. :-/
Sometimes it will turn out better than other times. I still think that every kitchen has different bacteria and it will always behave differently depending on the time of year or the temperature of the house, or the starter, or whatever.
So don't get discouraged if it doesn't turn out quite how you expected. Experiment and try again. Perhaps incubate it for a shorter (or longer) period of time. Or try more or less starter. Just have fun!
I'm not a pro...and our yogurt gets this amazing amount of whey after it's done, and I'm not sure how to eliminate it. But at this point in my life, I don't fret about it. *Maybe someday I'll devote myself to making non-wheyie yogurt. :)
Anyway, once it's done incubating, you can eat it. :) Sometimes we add a dash of vanilla for flavoring. Some folks add sugar. Or maple syrup. Here's a picture of what we did with ours right after I made it recently:
(Homemade canned cherry pie filling, with cinnamon sprinkled on top. For breakfast. Yum.)
Remember to reserve a bit of yogurt from this batch to use as your starter for the next one! You can do that for a few batches, but then we usually get a new starter, 'cause it seems to fizzle out and needs a boost after a while.
So, here's the basic recipe for Homemade Yogurt:
Slowly heat 1 gallon of milk to 180 degrees. Let cool to 110 degrees. Stir in 1/2 cup prepared yogurt as starter and mix well. Pour into jars and incubate around 90 degrees for 6-9-12 hours. Enjoy!
*(If anyone has any suggestions or tips on that, let me know in the comments!)