Make a homemade buttermilk substitute by combining 8 fluid ounces of milk with 4 1/2 teaspoons of white vinegar and allowing the mixture to stand for 15 minutes. Alternatively, use lemon juice in place of the vinegar.
This homemade cultured milk is not as thick as commercially available buttermilk, but it serves the same purpose in most recipes. If you prefer a thicker mixture, you can thin out three parts plain yogurt or sour cream with one part milk.
In baked goods, buttermilk serves the purpose of producing a light, airy finished product. The acid in the buttermilk interacts with baking soda to produce bubbles that lighten the batter, making it an important component of baked goods such as pancakes and biscuits.
Historically, manufacturers use the term "buttermilk" to refer to both the milky fluid left over during the production of butter and whole milk marked for butter production because it soured slightly, making it no longer suitable for drinking. The definition of buttermilk as cultured whole milk came about in the 19th century with the rise in popularity of baking soda as a substitute for yeast in baked goods. Since baking soda requires an acid to activate its leavening properties, cultured milk became a necessary commodity in many kitchens.
In modern times, manufacturers use low-fat milk in most commercially available buttermilk products, since the culturing process gives the milk a thick, creamy texture without the need for fat.