Question: are buttermilk and milk interchangeable?
Answer: Because the proteins in buttermilk are curdled, buttermilk is slightly thicker than regular milk, but not quite as thick as cream. ... Cultured buttermilk, as it is called in the United States these days, is a pasteurized milk product. A culture of lactic acid bacteria is added to low-fat milk to curdle and sour the milk.