Is Milk an Acid or a Base?

pH of Milk

Milk is slightly acidic.
Milk is slightly acidic. Joseph Clark, Getty Images

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. 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 slightly acidic response.

As milk "sours", its acidity increases. Harmless lactobacillus bacteria use the lactose in milk as an energy source. The bacteria combine it 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 whether milk is skim, whole, or evaporated. Colostrum is more acidic than regular milk (less than 6.5 for cow's milk).

What Is the pH of Milk?