Buttermilk is a fermented milk that is slightly sour and tangy, not unlike sour cream or yogurt. Although commercially produced buttermilk differs greatly from the homemade version of days gone by, it was originally prized for its usage in baking because it could make pancakes and waffles rise well.
Today when you buy buttermilk, there is a sell-by date on the carton. How long past the sell-by date should the buttermilk still be safe to use? How can you tell if it has gone bad?
Shelf Life of Buttermilk
According to the USDA, buttermilk can be kept in the refrigerator for about two weeks. It can also be frozen for up to three months.
Keep in mind that the buttermilk could have been mishandled in shipping or at the store, left out at room temperature. In this case, it may go bad sooner than two weeks past its sell-by date.
How soon you should use buttermilk depends on whether you want to drink it or use it in uncooked or cooked dishes. For using in drinks and uncooked dishes (like buttermilk ranch dressing), buttermilk is best while it is freshest. As buttermilk ages, it thickens and begins to lose its buttery flavor qualities. It can still be used for baking and meat tenderizing, which depend on its acid qualities.
How to Tell If Buttermilk Has Gone Bad
Once your buttermilk is chunky, and you can't pour it, or if it has visible mold, it's time to throw it out. Another sign is a strong sour odor.
Buttermilk today is made by introducing an active culture of lactic acid-producing probiotic bacteria to dairy milk that has been pasteurized to kill off most of the other bacteria that could be in the milk. The lactic acid gives buttermilk its tangy flavor and also acts to keep any other bacteria and molds from multiplying. The probiotic bacteria also produce diacetyl, which gives it a buttery flavor. Buttermilk continues to ferment throughout its time in your refrigerator, losing the buttery flavor while the lactic acid continues to be produced, making it sour.
How to Extend the Shelf Life of Buttermilk
Keep buttermilk refrigerated and don't let it sit out at room temperature. An unopened carton will last longer than an opened carton. Use good hygiene when you open the carton and pour from it—keep your fingers away from the lip of the carton, and never drink straight from the carton. Those are habits that can introduce bacteria, yeast, and mold to the buttermilk.
You can freeze buttermilk if you want to use it in baking. Freezing it will alter the consistency and cause it to clump and separate, so you won't want to use frozen buttermilk for drinking or uncooked recipes. It will still have its acid content which is what is desired for baking, as it helps the baked products rise. You can also use it for tenderizing meat.
If you are tired of having your buttermilk go bad before you're done using it, switch to powdered buttermilk. It has a very long shelf life at room temperature. You can make just what you need, so there's never any waste. Powdered buttermilk is usually used in baked goods rather than for drinking. Or, you can use alternatives to using buttermilk.