What if buttermilk is past the date on the carton?

If buttermilk is past the date on the carton, it may still be safe to use if it has been stored properly and shows no signs of spoilage, such as an off smell, unusual texture, or mold. Buttermilk can often last beyond its expiration date due to its acidity, which helps inhibit bacterial growth. However, it's always best to perform a smell and taste test before using it in recipes. If you're unsure, it's safer to discard it.