The Great Bake 
As buttermilk is one of the crucial ingredients, many pastry chefs have tried to develop various alternatives that still achieve just enough of the cake’s signature acidity. Here are some common substitutes for buttermilk.
Soured Milk
Stir vinegar or lemon juice to milk. Allow it to stand for 5 minutes, and soon it will begin to thicken.
Soured Milk with Cream of Tartar
Add cream of tartar to milk, stir, and allow it to stand at room temperature for about 5 minutes before using.
Sour Cream Buttermilk
Some chefs commonly swap buttermilk for something similar, like sour cream. Just be sure you keep the same measurements for each recipe!
Greek Yogurt Buttermilk
If you use Greek yogurt as a buttermilk substitute, it will need to be thinned slightly with regular milk. Stir the milk and Greek yogurt together and then use as directed in the red velvet recipe.
Powdered Buttermilk
Powdered buttermilk is helpful for those who don’t use it that often as it’s non-perishable. SACO is a popular brand many bakers recommend and is excellent for traveling.
Simply add the SACO powdered buttermilk to the cake’s dry ingredients, and then add in a suitable amount of water with the wet ingredients.
Dairy-Free Buttermilk Substitute
Mix about six ounces of dairy-free yogurt, two ounces of almond, soy, oat, coconut, or rice milk, and ½ teaspoon of white vinegar. Mix until thoroughly blended and let it stand for five to ten minutes before using.
