The process of making processed, or cultured, buttermilk is similar to that of yogurt. Lactobacillus is added to whole milk and allowed to ferment for 12 to 14 hours at low temperature. Salt and butter flecks may be added to the final product for flavor and texture. Here is a very simple recipe in which you can create your own buttermilk using common ingredients.
Ingredients to make buttermilk at home:
1 cup milk
1 tablespoon vinegar or lemon juice
Pour milk into a 1-cup measuring cup
Add 1 tbsp. white vinegar or lemon juice
Let the mixture stand for five minutes
Use in the recipe of your choice!