We started making our own yogurt a little while back. It is MY FAVORITE THING TO EAT ON THE PLANET (besides frosting)!
This is so easy to make, it is cheap and has nothing in it but milk! Seriously, this is it:
1. Heat milk up to 180 degrees.
2. Let it cool to 110 degrees.
3. mix in yogurt (from your last batch, or store-bought if this is your first time). I add about 1 1/2-2 cups if making a gallon. For a half gallon, of course, 1 cup would do fine.
4. Pour into clean jars, bowls, whatever.
5. Maintain at 110 degrees for 6-10 hrs. I place mine into my picnic cooler, add 2 closed mason jars of hot water beside them and place towels around those jars. Shut the cooler and go to sleep for the night. In the morning I put the yogurt in the fridge to chill.
You can strain the yogurt through a cheese cloth if you like greek-style yogurt. This stuff is great! For $2.50 I can have a gallon of yogurt without additives! You can add fruit, any sweetener you like or just eat it plain. But you may never want store-bought again!