c. sour milk or buttermilk
Low in fat (typically 0.5-1% in traditional buttermilk) while providing good quantities of calcium, potassium, and B vitamins. Contains beneficial probiotic bacteria from fermentation, though heat treatment in commercial products reduces living cultures.
About
Buttermilk is the liquid byproduct that remains after churning butter from cultured or fresh cream, though modern commercial buttermilk is typically made by fermenting milk with lactic acid bacteria (Lactococcus lactis). Traditionally produced in butter-making, authentic buttermilk is thin, tangy, and low in fat, with a white to slightly yellowish appearance and a distinctly sour, acidic flavor profile. Contemporary cultured buttermilk, the most common form in retail markets, is made by inoculating pasteurized milk with bacterial cultures and allowing it to ferment for 12-24 hours, developing acidity and a creamy texture while remaining thinner than yogurt. The resulting product typically contains around 0.5-1% fat in traditional versions and is rich in lactic acid, which gives it its characteristic tang.
Sour milk, a related fermented product, develops naturally when unpasteurized milk is left to sour at room temperature through the action of wild lactic acid bacteria. In culinary contexts, sour milk and buttermilk are often used interchangeably, though sour milk may develop a more pronounced curd separation and stronger sour flavor depending on fermentation conditions.
Culinary Uses
Buttermilk and sour milk are fundamental to baking and cooking, prized for their acidity, which reacts with baking soda to produce lift and tenderness in cakes, biscuits, pancakes, waffles, and quick breads. The lactic acid tenderizes gluten strands and creates flaky, moist crumb structures. Beyond baking, buttermilk is essential in Southern and traditional cuisines for marinating fried chicken, contributing to the characteristic tang and tender texture of the meat. It is also used in salad dressings (particularly ranch-style preparations), cold soups (such as Lithuanian šaltibarščiai), sauces, and whipped toppings. In baking, buttermilk can be used in ratios roughly 1:1 with regular milk, adjusting other ingredients as needed; when substituting for milk in recipes, reduce sugar slightly as buttermilk imparts acidity.