Allow to sit at room temperature until the milk thickens.
Add 1 Tbsp of white wine vinegar or apple cider vinegar to 1 cup of milk.For those who do not (including myself), the best route will be #4, and saving some from each batch to re-culture another one. Note: If you have an affordable source of raw milk, either #1 or #3 will be your most frugal options. Combine 1 Tbsp of store-bought buttermilk per 1 cup of fresh milk and allow to thicken at room temperature.Culture and re-culture several batches of milk until the milk thicken dependably and tastes tart, but not bitter. Allow raw milk to sit at room temperature to clabber.Buy a starter culture and combine with fresh milk.
The liquid byproduct is cultured buttermilk.