Dating on buttermilk is most often used to indicate to retailers how long to display the product before removing it from store shelves. Buttermilk's high acid content means it has a long shelf life and should maintain an acceptable taste and texture for at least as long as seven days after the sell-by date. When stored properly, buttermilk may last for even longer. If you notice clear signs that the buttermilk is bad, it's best to throw it out, but there are a few uses for buttermilk after the milk is expired as long as it hasn't spoiled.
Inspect the buttermilk before using it for taste and appearance. If the buttermilk is too thick to pour, has mold in it or has an unpleasant, strong odor, throw it out.
Add the expired buttermilk to cooked recipes that call for buttermilk in the ingredient list. Some baked goods that typically use buttermilk include pancakes, pies and biscuits. Buttermilk is sometimes used as a meat marinade since the acids and enzymes in the milk tenderize meat.
Freeze the buttermilk if you do not plan to use it within a few days. Buttermilk should last up to 2 months in the freezer. Thaw buttermilk in the refrigerator and use it in baking or other cooked recipes.