What Is Buttermilk?

Buttermilk is thicker than regular milk and coats a glass. Some buttermilk has a slightly creamy color, compared with the blue-white color associated with milk.
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What is buttermilk? You might think it contains butter, but it's really the result of a chemical reaction in any milk, including fat-free milk. So, whether or not there is butter in it depends on the type of milk that is used.

Buttermilk gets its name from the way it is produced. Buttermilk is the slightly sour liquid that is leftover from churning butter. Since butter is the fatty portion of milk, buttermilk is relatively low in fat even when made from whole milk. The type of buttermilk made using butter sometimes does contain small flecks of butter, however, most buttermilk sold in stores is made by adding Streptococcus lactis, Leuconostoc citrovorum, or Lactobacillus bacteria to milk to curdle it into buttermilk. This type of buttermilk could contain milk fat or be fat-free or anywhere in between.

Chemical Change in Buttermilk

When buttermilk is made from butter, the milk sours naturally from bacteria present in the liquid. When bacteria added to milk to produce buttermilk, the bacteria ferment lactose, the primary sugar in milk, producing lactic acid. Lactic acid reduces the pH of the milk, causing the casein protein to precipitate. The acidity makes the milk taste sour, while the precipitated protein thickens the milk, essentially curdling it.

Other Buttermilk Ingredients

Buttermilk from stores frequently contains salt, added flavoring, and sometimes colorings to impart a golden or "butter" color. Water, sugar, salt, curry, and asafoetida are among the most common additives. Buttermilk is available in a dry powdered form, too, which may be rehydrated and used in recipes.

Making Homemade Buttermilk

If you want to make authentic homemade buttermilk, churn butter and collect the liquid.

However, you can make buttermilk for recipes by simply adding 1 tablespoon of vinegar or lemon juice to any type of milk. The acid from the liquid ingredient acts the same as the acid produced by bacteria in natural buttermilk, thickening it. If you want the butter-yellow color of buttermilk, add a bit of yellow food coloring or a golden spice, as the recipe allows.

Whichever method you use, refrigerate buttermilk until use. It is naturally a bit sour but will become more acidic at warm temperatures.

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Helmenstine, Anne Marie, Ph.D. "What Is Buttermilk?" ThoughtCo, Aug. 27, 2020, thoughtco.com/buttermilk-does-it-contain-butter-607425. Helmenstine, Anne Marie, Ph.D. (2020, August 27). What Is Buttermilk? Retrieved from https://www.thoughtco.com/buttermilk-does-it-contain-butter-607425 Helmenstine, Anne Marie, Ph.D. "What Is Buttermilk?" ThoughtCo. https://www.thoughtco.com/buttermilk-does-it-contain-butter-607425 (accessed February 1, 2023).