Vinegar is sometimes used in cake recipes that call for both baking soda and baking powder because it can react with the leavening agents to create carbon dioxide gas. This gas helps the cake rise and creates a lighter texture.
Baking soda (sodium bicarbonate) is an alkaline ingredient that requires an acid to activate its leavening properties. When combined with an acid, such as vinegar, buttermilk, lemon juice, or yogurt, baking soda undergoes a chemical reaction that produces carbon dioxide. The carbon dioxide gas bubbles expand in the batter, causing it to rise.
In recipes that include both baking soda and baking powder, the vinegar serves as an additional acid ingredient to react with the baking soda, enhancing the leavening process. This can contribute to a more tender and airy texture in the final cake.
It's worth noting that not all cake recipes require vinegar, and it is typically used in specific types of cakes, such as certain chocolate cakes or red velvet cakes, where its acidity complements the flavors. The use of vinegar in cake recipes is a technique to achieve a particular result, and the specific recipe instructions should be followed for best results.