Essentially ground cacao beans, natural cocoa powder is very acidic. It needs to be neutralized by including an alkali (usually baking soda) in the batter. The reaction between the acid and alkali make carbon dioxide, which helps the batter rise. Hershey’s, in the brown container, is a widely available brand of natural cocoa powder; Scharffen Berger is a fine boutique product. Most of our recipes use natural cocoa.