Is there a substitute for cream of tartar?

You can often replace cream of tartar with distilled white vinegar or lemon juice. When cream of tartar is used to add volume and stabilize and whiten whipped egg whites, as with an angel food cake, replace every 1/8 teaspoon of cream of tartar (the amount needed per egg) with 1/2 teaspoon lemon juice or distilled white vinegar.

Cream of tartar is also called tartaric acid and is scraped from the inside of wine barrels.