Buttermilk got its name from the fact that it was originally the liquid left over when making butter, but nowadays, as it is mainly commercially made, this liquid has very little to do with butter. A bacteria is added to milk and then left to ferment. Bits of butter may be added, as well as salt, sugar, and stabilizers creating what we know as cultured buttermilk.
Unlike regular milk, buttermilk does not stay fresh as long—combine this with the fact that we don't normally use the entire container buttermilk in a recipe, or buttermilk that often, and we end up with leftover buttermilk.
So what is the best way to store it?
Buttermilk's Shelf Life
Buttermilk will last up to two weeks due to its high acidity level, although it is best the first week. Once opened, it should be used within a week for drinking purposes, but it should be fine for baking even after the expiration date. Always look for the latest expiration date on the carton, just as you would for any dairy product.
Like most dairy products, buttermilk should be kept refrigerated; do not let it sit out on the counter or the kitchen table for any length of time.
But what do you do with that 3/4-full container, knowing you are not going to make anything with buttermilk in the next week or two? Fortunately, like milk, buttermilk can be frozen up to three months. If you only use buttermilk for certain recipes and know the measurements, you can portion it out to accommodate those dishes, and then freeze.
Otherwise, pour the remaining buttermilk into an ice cube tray—in one tablespoon portions—and freeze. Then place the cubes in an airtight freezer bag until ready to use.
If you do freeze buttermilk, let it thaw in the refrigerator, or do a quick defrost on low in the microwave. Just be sure to mix it well to reincorporate the solids with the liquid which will have separated.
Although it will be perfectly safe to drink, you may prefer to use previously-frozen buttermilk in recipes rather than for a beverage, as it tends to lose texture and mouth-appeal.
If this all seems like too much to remember, there is an alternative: buttermilk powder, which you can find in your grocery store. Basically dehydrated buttermilk, buttermilk powder has an admirable shelf life, almost indefinitely on the shelf unopened and up to a year and even longer after opening when stored in the refrigerator. Buttermilk powder is generally used for baking rather than drinking.
More About Buttermilk
Perhaps after all this, you realize you forgot to buy buttermilk, or someone decided to clean out the fridge and tossed it. No worries—there are plenty of buttermilk substitutions and equivalents. And if you are wondering whether to include it in your recipe or not, you may be happy to learn there are certain health benefits to buttermilk.