Does buttermilk go bad? Shelf life and signs of spoilage

You bought a quart of buttermilk for a batch of pancakes, used one cup and now have the rest sitting in your fridge. The prescription for which you bought it is ready. The date on the carton is fast approaching, and you’re not sure whether you should use it, throw it away, or whether it was already questionable to begin with. So does buttermilk go bad?

Does buttermilk go bad?

Short answer: Yes, buttermilk goes bad, but its natural acidity gives it a longer and more durable shelf life than regular milk. An opened carton lasts for 1 to 2 weeks in the refrigerator. Unopened buttermilk is generally good for 1 to 2 weeks after the printed date. Spoiled buttermilk develops a blue-green mold, a strong foul odor distinct from its usual astringency, or a thick, shiny texture that does not thin out when stirred.

See the Food Storage Guide for more information on storing dairy products.

How long does buttermilk last?

Buttermilk is a cultured dairy product, meaning that lactic acid bacteria are added to pasteurized skim milk to create the sour, slightly thick product you buy at the store. That acidity is what gives buttermilk its distinctive flavor, and it’s what makes buttermilk keep longer than regular milk. The low pH (about 4.5) creates an environment that slows the growth of bad organisms.

According to USDA Foodkeeper, buttermilk keeps for 1 to 2 weeks refrigerated. America’s Test Kitchen, which conducted extensive research on this topic with dairy industry experts, found that buttermilk will not actually spoil (meaning visible mold will develop) for at least three weeks after opening when kept constantly refrigerated. University extension programs generally recommend consuming buttermilk within three weeks of the date printed on the package.

The practical answer for most people: Use it within two weeks of opening, trust your senses as to the date, and freeze anything you won’t finish in time.

How to tell if buttermilk has gone bad

Buttermilk is naturally sour, slightly thick and slightly lumpy. These are not signs of deterioration. They are what fresh buttermilk looks and smells like. The challenge with buttermilk is that all of its common characteristics match those of other dairy products with signs of early spoilage. Here’s how to tell the difference.

Normal vs. Bad: Main Differences

Most people throw away perfectly good buttermilk because they misunderstand the general characteristics. Here’s a clear side-by-side:

The easiest test: Shake the carton vigorously. Fresh buttermilk, even if separated, will recombine into a pourable liquid. Bad buttermilk will not be made.

Can you freeze buttermilk?

Yes, and unlike half and half or heavy cream, buttermilk actually freezes quite well for baking and cooking purposes. America’s Test Kitchen recommends the ice cube tray method: Pour buttermilk into ice cube trays, freeze until solid, then transfer the cubes to zip-top freezer bags. Each standard cube is about 2 tablespoons, making it easy to scoop out just what you need for a recipe without melting the entire batch.

Frozen buttermilk can be stored for up to 3 months and is used straight from frozen in cooked applications: pancakes, biscuits, waffles, quick breads, marinades and salad dressings. While its texture changes slightly after freezing and thawing, making it less ideal for drinking straight, for baking it performs well in most applications with minimal quality difference. Thaw in the refrigerator overnight or drop frozen cubes directly into hot batter.

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Why does buttermilk last longer than regular milk?

The extended shelf life of buttermilk comes from its acidity. The lactic acid bacteria used to culture it produce lactic acid as a byproduct, which lowers the pH to about 4.5. Most bad bacteria and pathogens do not thrive at that pH level. The pH of regular milk is around 6.7 to 6.9, which is a much more favorable environment for bacteria. This is why dishes that use buttermilk as a marinade (e.g. buttermilk fried chicken) are so effective: the acidity helps tenderize the meat while the low pH slows the growth of bacteria on the surface.

This does not mean that buttermilk is immune from spoiling. Once enough time passes or storage conditions deteriorate, the natural acidity of the buttermilk is also taken away by molds and other organisms that thrive in acidic environments.

What about buttermilk powder?

Buttermilk powder is a completely different product from liquid buttermilk, and it’s worth knowing about if you occasionally bake with buttermilk but don’t finish the carton in time. Dried buttermilk powder has had its moisture lost, leaving solids and the same acidic, tangy flavor profile. Unopened it lasts for 1 to 2 years at room temperature. Once opened, transfer it to an airtight container and store it in the refrigerator to extend its life up to 6 to 12 months.

In baked goods, add powder to dry ingredients and add water in place of liquid. Most brands, including SACO, call for 4 tablespoons (1/4 cup) of powder per 1 cup of water to mimic 1 cup of buttermilk. Its flavor is very close to fresh, although some bakers find it slightly less spicy in the finished product.

Recipes That Use Buttermilk

If you have a carton near the end of the window, use that. Buttermilk works in this Cinnamon Pecan Crunch Banana Bread, and it’s excellent in pancakes, biscuits, fried chicken marinade and any quick bread that requires baking soda, because the acid reacts with the soda to leaven. Beyond baking, add a little to mashed potatoes instead of regular milk for a more flavorful result, add it to soups in place of cream for a lighter body, or use it as a base for a simple salad dressing with olive oil and herbs.

FAQ: Is it OK to use buttermilk after the expiration date?Often yes, for baking and cooking. The natural acidity of buttermilk means it is more forgiving than most dairy products after its printed date. An unopened carton that has been kept refrigerated continuously may be good for 1 to 2 weeks after the date. An opened carton depends on when you opened it: regardless of the date, use within 2 weeks after opening. Always check the smell and texture before using. For drinking or using in cold preparations such as salad dressings, stay close to the date for best flavor.

FAQ: Why does buttermilk smell sour? is that bad?No, buttermilk has a sour smell. It is a fermented dairy product made by culturing milk with lactic acid bacteria, which produces lactic acid as a byproduct. Lactic acid is responsible for both the pungent odor and extended shelf life. A mild to moderate sour smell is completely normal. The odor indicating spoilage is stronger, more rancid, or really unpleasant that is markedly different from the taste of normal buttermilk. If you’re unsure, shake the carton and check the texture. If it flows normally and the smell is only mildly sour, it is almost certainly okay.

Further reading