Step 3: Bring Milk Just to a Boil.
To make a quart of yogurt you will need 4 cups of milk. Any kind will do (yak, cow, goat, nonfat, whole, whatever.) Bring the milk just to a boil while stirring to prevent a surface from forming on the liquid. Boiling innoculates the milk, which eliminates any bacteria that might compete with the yogurt bacteria during the incubation process.