According to a Dietitian

Cream of tartar works best as a substitute for buttermilk when it is combined with milk because of its powdery consistency. The most commonly cited substitute for buttermilk adding an acidic ingredient like lemon juice or vinegar to plain milk will add a nice tang and curdle the milk to make it slightly thicker. 6 Easy Buttermilk Substitutes How To Make Buttermilk Good Life Eats In recipes that call for buttermilk it is not recommended to replace buttermilk with plain milk because the absence of acid will not produce the same end result. Sub for buttermilk . Milk Lemon Juice or Vinegar. Modern buttermilk is a combination of water milk lactose and casein. We suspected a one-for-one substitution would work but to be sure we did side-by-side tests with biscuits pancakes yellow cake and cornbread. It could be Apple cider vinegar or distilled white vinegar. It will depend on your recipe and how much moisture you need. Here are some standbys. Instead the name derives fr...