Science, Tech, Math › Science Do You Know If Milk Is an Acid or a Base? What's the pH of Milk? Share Flipboard Email Print Fa Romero/Pexels 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 May 11, 2019 It's easy to get confused about whether milk is an acid or a base, especially when you consider that some people drink milk or take calcium to treat an acidic stomach. Actually, milk has a pH of around 6.5 to 6.7, which makes it slightly acidic. Some sources cite milk as being neutral since it is so close to the neutral pH of 7.0. However, milk contains lactic acid, which is a hydrogen donor or proton donor. If you test milk with litmus paper, you'll get a neutral to a slightly acidic response. The pH of Milk Changes As milk "sours," its acidity increases. Harmless Lactobacillus bacteria use the lactose in milk as an energy source. The bacteria combine with oxygen to produce lactic acid. Like other acids, lactic acid has a sour taste. Milk from mammalian species other than cattle has a comparable slightly acidic pH. The pH changes slightly depending on whether milk is skim, whole, or evaporated. Colostrum is more acidic than regular milk (less than 6.5 for cow's milk).