This is a recipe you can follow if you need to make a large quantity if plain yogurt at once. It is definitely not for those who need to make a cup of yogurt as an example.
1/2 gallon of whole milk
1 cup of yogurt culture
Add half a gallon of milk to the crockpot
Turn the crockpot on high for 2 1/2 hours or until the temperature is between 175 to 180 degrees Fahrenheit.
Turn off the crockpot and let the milk cool till the temperature drops to 110 degrees Fahrenheit.
Remove any cream from the top of the milk.
Add one cup of yogurt to the milk.
Wrap the crockpot in a towel and place the crockpot in an unused oven. It is important that you do not turn on the oven.
Leave aside for around 10-12 hours. The yogurt should set by then. Put the yogurt in the fridge for future use.