2 Tablespoons of Yogurt with Live and Active Cultures
2 Quarts of WHOLE milk- this matters for the thickness of the yogurt.
Actually, that's all you need. :) So here's my method...
1. With the stove burner on low, pour the milk into a pot and slowly warm it to the temperature that you would serve a baby a bottle at. I do the 'wrist test' and if it feels right for a baby it is perfect to get the cultures in your yogurt multiplying- that's 110 degrees if you have a thermometer. I don't think you have to worry about scalding your milk prior to this step, as some other people suggest. Oh wait- I'm not here to debate the proper methodology of yogurt making. I'm just telling you what works for me.
2. Whisk in 2 tablespoons of your starter yogurt. If the milk is too hot, it will kill the live cultures that are what turns milk into yogurt.
3. Pour the cultured milk into two quart jars and place them into a cooler.
4. Wrap the cooler up in a heavy blanket. This incubates them and keeps the temperature where it needs to be for your cultured milk to turn into yogurt.
5. Leave the yogurt in the cooler for 12 hours, somewhere room temperature (60-75 degrees). If you leave it in the cooler longer than 12 hours you will end up with a bit of a more sour yogurt, but that's your preference. 12 hours seems to be the perfect number for me. Heads up, if you start the process at 1 o'clock in the afternoon you're going to need to wake up in the middle of the night to unwrap your baby yogurt from its blankie and put it back to bed in the fridge. I already have three kids so I try to avoid that but its happened.
When your yogurt is done, it will still appear pretty liquidy. Give it a big stir and put it in the fridge. It will thicken up some but still be a little bit less firm than commercial yogurt. If you prefer, drain some of the liquid off by pouring your yogurt over a bowl draped with a cheesecloth. You can save the liquid that runs into the bowl and use it for baking. HAHA. Or you can throw it away (guilty). Don't forget you can save a half cup of your final product to use as a starter for your next batch.
We use our yogurt in smoothies before straining, and I serve it in bowls after straining. This is plain yogurt, so if you like sweetness without a ton of sugar you can squeeze in some honey or agave nectar, plus fresh fruit. You can also just add sugar!
If you have questions or need to trouble shoot, be sure to comment and I can try to help you. There are TONS of helpful solutions on Google ranging from using gelatin to dry milk. I have found making your own yogurt is a trial and error thing that I've invested a bit of time in, so if at first you don't succeed have a cry and try again.