What is commonly required to make regular milk behave like buttermilk in recipes?

To make regular milk behave like buttermilk in recipes, the addition of an acid is required. Buttermilk itself is a fermented dairy product that has a tangy flavor and a lower pH due to the presence of lactic acid. When you add an acidic ingredient to regular milk, it curdles slightly and develops a similar consistency and acidity to buttermilk.

Lemon juice is a common kitchen acid that can be used for this purpose. When mixed with milk, it will create a reaction that causes the milk to sour and thicken, effectively mimicking the properties of buttermilk. This substitution is widely used in baking recipes where buttermilk is called for, as it helps in activating baking soda for leavening and adds flavor.

While vinegar also serves as an acid that can curdle milk, it's typically less favored in recipes compared to lemon juice because of the stronger flavor profile. The mention of baking powder and salt does not apply to this process, as they do not have the ability to replicate the acidity of buttermilk.