Instructions

1. Purchase 6 to 8 ounces of cultured buttermilk for each new quart you make. Be sure the carton says, "active cultures"; some dairies kill the cultures during bottling. You'll also need 3 cups of any kind of store-bought milk you want to use. Since the culturing process will thicken your mixture, if you choose to use whole milk, it will be thicker than store-bought buttermilk -- most commercial buttermilk is make with skim milk.

2. Pour 3 cups of fresh milk into a clean quart jar (or use the carton that your store-bought milk or buttermilk came in). Add 6 to 8 ounces of cultured buttermilk to the jar.

3. Shake the jar to mix. Leave it for at least 24 hours at room temperature. Yes, it's OK to do this -- nothing bad will happen to your milk -- in fact, it's necessary for the bacteria cultures to properly do their work. Remember, these are good bacteria, and their activities will not make you ill.

4. Taste your buttermilk. It should be tart, and thick enough that it clings to the inside of a glass. If you don't think it's tart enough, you may leave it for another 12 hours. If it still is not tart enough, perhaps your buttermilk was old, and the cultures in it have died, or perhaps your buttermilk did not have "active" cultures. But 36 hours should always work with a live cultured buttermilk.