If using raw milk, heat the milk to 185 degrees F and let cool to 110-115 degrees F. You can do this with pasteurized milk as well which will yield a thicker yogurt, but it is optional with pasteurized and ultra pasteurized milk.
Add the culture to the cooled milk and mix well. This should be store-bought unflavored yogurt with no other added ingredients.
Pour this mixture into the bread pan of the bread machine.
Close the lid and choose the yogurt cycle or warm cycle.
If you have neither of these programs, customize the bake setting temperature to between 110-115 degrees.
Set time to between 8-12 hours.
Once the cycle is complete, pour the yogurt into a yogurt strainer for 2-3 hours for a thicker yogurt. This step is optional, however.
Store the yogurt in an airtight container in the fridge. Let cool before consuming for best results. See notes for storage time.