In the past, buttermilk referred to the liquid that was left behind after churning butter. What we find in supermarkets today is actually nonfat or low-fat milk to which cultures have been added, rendering it thick and tangy. We consider buttermilk a dairy-aisle superstar: Its tenderizing capabilities produce perfect baked goods and must-try marinated meats. A natural emulsifier and thickener, it creates a creamy texture in soups , smoothies, and salad dressings.
Keep buttermilk up to 2 weeks in the fridge, or freeze it up to 3 months. Use thawed buttermilk for baking.