When lactic acid-producing bacteria is added to cream, it produces the slightly tart, thick substance known as sour cream. Commercially produced sour crams most always contain rennet and other flavor additives.

Lighter fat creams made with half and half, non-fat milk and soy are available to reduce the fat content. Sour cream serves as a tempering agent, particularly in baked goods or as  foil for spice and heat in a recipe.