Originally made from the liquid leftovers from the butter-making process. Current-day buttermilk is made by adding bacteria into milk, which causes fermentation. Buttermilk is tangy, thick, and sour.
Most likely central Asia, made by nomadic people who domesticated cattle for milk. Buttermilk then spread to Europe and India.
Traditional buttermilk is a popular drink in areas of India, Nepal, and Pakistan.
Cultured buttermilk was first commercially introduced in the United States, where milk is often pasteurized, eliminating much of its bacteria.
“All Churned Around” by L.V. Anderson (2012)
Food, Fermentation, and Micro-Organisms by Charles W. Bamforth (2005)
“Is Buttermilk Good for You?” by Lauren Panoff (2019) www.healthline.com/nutrition/buttermilk