(p.s. This instructables version is better than the version on my blog, but I always include a link just in case you feel like visiting.)
- 1/2 gallon of whole or 2% milk that is not Ultra-Pasteurized (This has to do with the temperature it was pasteurized at. If milk has been Ultra-Pasteurized it must be labeled that way, so it's generally easy to avoid. The only organic milk I've found in my neighborhood that will work is from Trader Joe's)
- 1 small plain, all-natural yogurt that has live cultures (like Nancy's)
- slow cooker or double-boiler
- small bowl, stirring spoon, and ladle
- an oven or closed space that you aren't going to need for 8 hours
- tea-kettle or pot with lid
- butter muslin or cheese cloth if you like thick (Greek-style) yogurt
- optional fruit to stir in
Step 1: Sanitize Your Equipment
Step 2: Heat the Milk to 180 Degrees
I tried skipping this step once because it's basically just to kill whatever bacteria might be in the milk (my reasoning was, I just specially bought non-ultra-pasteurized milk, why would I heat it up so high now?), but the yogurt didn't work. It was really sticky and separated and not yogurt-sour, but strange sour.
Step 3: Cool the Milk to 110 Degrees & Add the Yogurt Starter
In a clean bowl combine the store-bought yogurt with 1 cup of the warm milk and mix well. Add this yogurt mix back to the slow cooker.
If you add the yogurt starter when it's too hot you'll kill the bacteria, cook the yogurt, and it won't combine. If this happens (because maybe you were excited and trying to skip steps) you can strain out the cooked yogurt (I thought it tasted kind of good), let the milk cool, and add more starter yogurt.
Step 4: Keep the Yogurt Warm and Undisturbed
Boil some water in the tea kettle or pot and put that in the oven too. This keeps my oven at a perfect 100 degrees.
Let this sit undisturbed for 6 to 12 hours, depending on how tangy you like your yogurt. I do 8 hours.
Step 5: Now You Have Yogurt!
If you think you might make another batch, save about 1/2 a cup for the next time instead of using a store-bought yogurt.
Step 6: Optional: Strain Yogurt to Thickens
Step 7: Optional: Add Fruit and Sugar
ps - I read that it's not a good idea to add honey to yogurt if you're going to store it in the fridge because the honey bacterias can kill the yogurt bacterias. Add honey to each serving right before you eat it. If anyone knows more about this, let me know.