to 1 1/2 cups buttermilk

Buttermilk is a tangy, slightly acidic dairy product traditionally produced as the liquid byproduct after churning butter from cream. The original traditional buttermilk, still produced in some regions, contains the residual liquid naturally present after butter solids coagulate. Modern commercial buttermilk, however, is typically cultured buttermilk—skim or low-fat milk fermented with lactic acid bacteria (Lactococcus lactis), which produce lactic acid and impart a characteristically sour flavor and thicker consistency. The ingredient has a sharp, mildly tangy taste and a creamy, pourable texture with a white or slightly off-white appearance.

Buttermilk's acidity and composition make it chemically distinct from regular milk and particularly valued in baking, where the acidity reacts with sodium bicarbonate (baking soda) to produce carbon dioxide gas, creating lift and tender crumb structures in quick breads, pancakes, and biscuits.

Buttermilk is fundamental in American, Southern, and Irish baking traditions, where its acidity activates baking soda to create fluffy biscuits, pancakes, waffles, and quick breads such as soda bread and cornbread. Beyond baking, it serves as a marinade base for fried chicken and other proteins due to its enzymatic acids, which tenderize meat. In sauces and dressings, buttermilk provides tanginess and body, particularly in ranch dressing and creamy salad dressings. It is also used in drinking form, particularly in South Asian cuisines (as "chaach") and Scandinavian traditions. Its acidity and richness make it suitable for gravies, soups, and pound cakes where both moisture and tender crumb are desired.