Bring milk up to 110 degrees Fahrenheit. Here’s where many recommend you first bring it up to 180 F to pasteurize (That is up to you and your researched decision.), then cool to 110 F (warm to the wrist, not hot).
Mix 1/2 cup organic yogurt with 1 cup of the warm milk, then pour the mixture into the rest of the milk, mixing well. If you want to make vanilla yogurt, now is the time to add 2 tablespoons homemade vanilla extract.
Pour milk into sanitized jars and put lids on loosely. Keep at 110 Fahrenheit for 6 hours without mixing, stirring, or moving if possible.
There are a few ways to do this (Choose one):
1. Put in a yogurt maker that keeps them at 110 Fahrenheit.
2. Put the jars in a large pot of water on the stove that is already at 110 degrees Fahrenheit and wrap towels around it to keep warm. I’ve done this before and it stays warm for a very long time. You just need to check occasionally and turn the burner on for a minute or two (but watch carefully) if it cools down too much.
3. Put the jars in the oven with the light on and place candy thermometer on the rack so you can see temperature. This usually stays at 110 Fahrenheit for about 4 of the 6 hours. If you turn the oven on, watch it very carefully.