Science, Tech, Math › Science What Is Buttermilk? Share Flipboard Email Print Roger Dixon / Getty Images Science Chemistry Chemistry In Everyday Life Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated January 17, 2020 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.