Note: You can make larger (or smaller) volumes as needed. I use a ratio of one tablespoon starter for every cup milk with reliable results. Unless your culture was not designed to be perpetuated (some freeze-dried options fall into this category), you can reserve a bit of each batch to culture the next.
Some recipes indicate that you should pasteurize your milk (at 180°F) before culturing or at least warm it to 76°F. This step is entirely unnecessary, as store-bought milk is all pasteurized before it hits the shelves.
- 2 tablespoons buttermilk (store-bought or activated dried starter)
- 2 cups milk (whole, 2%, or skim, depending on your nutritional needs and preferences)
In a mason jar or other glass container, thoroughly mix the starter and milk. Cover with a coffee filter or piece of cheese cloth (do not seal tightly with a lid) and leave to culture out of drafts at a warm room temperature (between 70-78°F is recommended) until milk has clabbered (10-24 hours).
To test if the milk has thickened, tip the jar slightly. It should move away from the wall of the jar as a single mass. Just as with yogurt making, once the milk sets, it will get more tart the longer you allow the culturing to continue.
Refrigerate to halt culturing for at least six hours. Stir before using.