- 1/2 gallon of milk
- 1/2 cup starter yogurt
- container(s) to store finished yogurt
I started with organic whole milk from the local grocery store. From other people's stories, as long as the milk isn't ultra-pasteurized you should be good to go for making yogurt. The higher temperatures of ultra-pasteurization do something to the milk that isn't good prep for bacteria reproduction. Homogenized, pasteurized, non-organic, and 2% milk are all fine.
The starter yogurt needs to have live bacteria in it for you to be able to make more yogurt from it. I used Stonyfield organic yogurt, but you can use any brand as long as it has "live" and/or "active" somewhere on the label, telling you those good bacteria can wake back up and reproduce. This particular one says "six live active cultures". Some people say you can't use flavored yogurt as starter, but I did and it worked... maybe because this one is "naturally" flavored? Whatever you use, it will all end up as a plain yogurt batch.
1. Pour half a gallon of milk into a clean crockpot. You can measure exactly if you want to, but I just eyeballed it.
2. Cover the crockpot and turn it on high. You want the milk to warm up to 180 degrees first, prepping it for bacteria reproduction. My crockpot has a nifty temperature probe, so all I had to do was set the desired temp. A regular kitchen thermometer (for meat or milk or whatever) works just fine too. Depending on your crockpot, it could take half an hour longer to warm up to 180.
3. When the milk is at the right temperature, turn off the crockpot and let the milk cool back down to 120 degrees. The yogurt bacteria will grow when the temperature is between 110 and 120. Too hot and the bacteria will die. Too cool and they'll go into hibernation.
4. When the milk reaches 120 degrees, take about a cup of the warm milk out, mix in the 1/2 cup of yogurt, and add back to the crockpot. Stir it together. Put the crockpot lid back on and cover it all with a towel for insulation.
5. Now wait. The bacteria just need time to grow and turn that milk into creamy yogurt. If your crockpot loses heat easily (or if you're just paranoid), you can check it every hour or so and turn the warmer back on for a few minutes to get it back into the 110-120 range. Just set a timer or something so you don't forget to turn it back off - you don't want to nuke the bacteria!
6. After as few as maybe 3 hours, you'll hopefully see that the milk is turning into yogurt. Water in the batch is perfectly normal. A lot of people just start the yogurt process before they go to bed, and wake up to put away the finished yogurt in the morning. It seems like the average wait is 6-8 hours, so that's what I shoot for too. Logically, the bacteria stop reproducing when the temperature falls out of the ideal range, so it may not matter much as the hours extend. Maybe there's a scientific reason for longer waits... go Google it if you feel the need.
7. When it's all done, just stir the yogurt and transfer it to your desired container. I use two glass quart jars, which is just perfect for the 1/2 gallon of yogurt.
8. Let the yogurt chill for however long (it usually takes me a day to get through previously-made yogurt anyway) and then enjoy! I love it with some chopped fruit and a bit of honey. Don't forget that you have to save 1/2 cup of your yogurt to make the next batch!