After three failures in a row with the homemade yogurt trials, I took a sabbatical. I finally got the courage to try again and I'm really happy I did. This stuff is really yummy.
3 1/2 cups organic whole milk
1/2 cup plain yogurt (good commercial quality or from previous homemade batch)
Heat milk to 180'. Cool to 110'. It took my yogurt about 30 minutes to cool down. Stir in yogurt. Pour into a quart mason jar. Incubate at least 6 hours and up to 24.
My incubator is this blue water cooler we have that I fill up with enough hot water to rise to the level of the yogurt once the jar is submerged. Currently, I incubate for 6 hours and the yogurt comes out nice and thick. In my first successful try, I only used 2 TB yogurt as the starter and incubated it for 24 hours. It was pretty thin - tho supposedly healthier for you because the bacteria had so long to work. If you like the consistency of your yogurt when it first comes out of the incubator, just put it in the fridge and eat it as-is.
If you want to thicken it up, you can strain it (like Greek strained yogurt in the stores). Line a sieve with cheesecloth (you can kind of see the silver sieve in the picture above). Put a bowl under the sieve and pour the yogurt in. Let it sit in the fridge for about three hours or until you like the consistency. Funnel the strained yogurt into one jar (the one on the left in the picture below) and the whey/thin yogurt mixture into another (the one on the right). Note: if you want to feel magic, let it drain in the fridge for 2-3 days or until it gets nice and thick. You can add a bit of salt and vanilla flavoring to the yogurt before draining for a homemade cream cheese or use salt and garlic powder for Greek labneh cheese.
I used the leftover whey mixture from straining to soak my oatmeal (pictured in the middle) and had my strained yogurt with some blueberries and honey. Delicious. As you can see, straining really reduces the volume and it's a hassle so it's not part of my regular yogurt making routine. I do feel like making homemade yogurt it worth the effort though. I now get 128 oz of organic, whole milk yogurt for $5.99 (the price of my gallon of milk). Awesome.
Update: Go here for directions on how to make yogurt in your crockpot!