We're glad you enjoyed this recipe, Kris! It's there for leavening, in combination with the baking soda. (And the brown sugar is an additional acid to work with the baking soda.) You could experiment with adding a small amount of vinegar to recipes calling for baking soda, but it would like just cut the sweetness rather than doing anything leavener wise, and there's a potential that you could taste it a little. 

We have 9 cake/cupcake recipes that call for vinegar. They're often but not always recipes that don't have eggs, so they rely on other forms of leavening. In the case of the Red Velvet Cake, vinegar helps make the color vibrant. 

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