Ever since I started making yogurt, I just can't eat store bought yogurt anymore. The yogurt I make at home is tart, fresh, and has a consistency like pudding... I just can't find any that yummy in the store! Here's how I make it...
I start with a half-gallon of organic milk. My current favorite is 2% because it has just enough fat to give it consistency without heaviness, but both whole and skim milk work fine, too. I heat it up to just below scalding (between 150 and 200 degrees F). Lots of people say you can skip this step, but I find that I get more consistent results when I heat it up past 150, it kills any residual beasties so that the yogurt cultures can go to work! Then I let the milk cool down to 115-120 degrees F. Any warmer and you risk killing your yogurt culture. If it is too cool the cultures will take longer to get to work.
While you're waiting for the milk to cool, you can get your jars ready. I like to use 500 ml canning jars. I think the jars that come with yogurt makers are too small... I like to have room to add a heaping pile of fresh fruit, and still have a hearty serving of yogurt. The canning jars are practically indestructible-- I take them to work for lunch on a regular basis, and haven't broken one yet. They're also great for other lunch items, and I love that they are all glass (no questionable plastics to leach chemicals), they almost never leak, and you can replace the lids when they get grimy.
You don't really need things to be sterile to make yogurt, just clean. But I hate being disappointed by a bad batch of yogurt, so I err on the side of overly clean. Since the lids have all sorts of little ridges that are hard to wash, I drop them in a pot with an inch or two of water, and steam them.
So when your milk is between 115 and 120 degrees F, you're ready to make yogurt. Skim off the skin on the top of the milk. I tried once to mix it in... bad idea. It just broke up into pieces, and there were little papery pieces of it all throughout the yogurt! Definitely skim it off, and discard.
Then, pour off a cup or so of milk into a small bowl, and add a heaping teaspoon of your favorite yogurt to be your culture. I use Fage greek yogurt, because I love the texture of it. The finished product isn't exactly like the greek yogurt because I don't strain it (I plan to try that someday!) but it is still pudding-like, not slimy like some other yogurts. You can freeze the rest of the starter to use in another batch, or you can just eat it! You can also use some of a previous batch of yogurt, but tend to forget to leave any behind. I'd rather start with an uncontaminated culture, anyway.
Add the one cup of milk that has the starter in it back into the main batch of milk, and stir well.
Pour the mix of milk and yogurt into your jars. I use 6 or 8 jars, depending on how large of a serving I want to make.
My filled jars. Now all you need to do is find somewhere warm and quiet to let the yogurt cultures do their work for 8 hours or so.
Dala is checking out my system. I use a styrofoam cooler-- the kind that drug companies use to send temperature-sensitive pills to patients-- and a heating pad on LOW. Many people suggest using an oven with the pilot light on, but I found that mine didn't keep my yogurt warm enough.
Here's the hard part-- wait for 8 hours! Sometimes I start my yogurt at night, and then it is done in the morning. The longer you let it culture, the more tart and firm your yogurt will be. Within reason... things start to get a little odd past 10 hours. If you like mild, soft yogurt, you can try 4 or 6 hours.
Here's the finished yogurt. The whey has separated and is on top, and the yogurt is nice and firm.
You can eat it right away-- there is nothing like warm, fresh yogurt. But if you plan to save them for a later date, refrigerate immediately. The yogurt will get even firmer in the fridge. I find that my unopened jars will keep for weeks in the fridge. Enjoy!