Traditionally, buttermilk is the leftover liquid that remains after straining milk fat during butter production. Despite its name, buttermilk is low in fat and a good source of protein, providing up to 8 grams in a single cup (250 mL).

Buttermilk has a tangy flavor and is naturally thicker compared with regular milk. Its higher lactic acid content lends itself well to baking, and the product is widely used in bread production, pancakes, and other quick breads.

It’s also widely consumed as a drink, made into cheese, or added to sauces and dips for a boost in flavor and smoother consistency.

However, because of its tangy taste, many people have trouble telling when their buttermilk has gone bad and is no longer safe to use.

The buttermilk you buy at your local grocery store also known as cultured buttermilk is usually different from traditional buttermilk originally produced on a farm.

Cultured buttermilk follows a similar manufacturing process to yogurt. Bacterial cultures (Lactococcus lactis ssp. lactis), salt, and citric acid are added to skim milk and ferment for 14–16 hours. This converts milk sugars into lactic acid, producing a tangy floor

In contrast, traditional buttermilk is a byproduct of the butter-making process. It’s the liquid that remains from separating the fat from cultured butter.

Compared with cultured buttermilk, traditional buttermilk is less tangy and sour.

Buttermilk must be pasteurized for sale in the United States, meaning it undergoes a heat treatment of 161°F (71.7°C) for at least 15 seconds, allowing for a longer shelf life and killing off harmful bacteria.

Though most buttermilk available in stores is cultured buttermilk, many chefs and culinary experts rely on traditional buttermilk for its better flavor and texture.

Cultured buttermilk is made from skim milk with added bacterial cultures, salt, and citric acid. In contrast, traditional buttermilk is the remaining liquid from cultured butter during the butter-making process.

Keeping an eye on the shelf life of buttermilk can ensure you’re getting the best and safest product.

Buttermilk contains lactic acid and a compound known as diacetyl, which both contribute to its tangy and buttery flavor. Over time, buttermilk continues to sour and the bacteria that produce diacetyl decline, resulting in a less flavorful product.

If you’re concerned that you won’t use your buttermilk before it expires, freezing it may be best. However, freezing buttermilk will alter the texture and flavor of your product and usually only works well in baking.

Avoid purchasing unpasteurized buttermilk which can increase your risk of foodborne illness.

Using buttermilk within its recommended time frame ensures your product tastes great and is safe to consume.

If you choose to freeze your buttermilk, you can freeze it in its original container as long as it has enough space. This helps the package to expand in the freezer and prevent it from bursting. Otherwise, ensure you put the buttermilk in a sealed, airtight container.

However, buttermilk may go bad before the expiration date due to improper handling, fluctuating temperatures, or other factors.

Buttermilk can last up to 14 days in the fridge after it has been opened and may last beyond its expiration date if unopened. However, it’s always best to use it as soon as possible.