Natural cocoa vs. Dutch process
If you've ever made a baked chocolate dessert with less-than-spectacular results, your cocoa may be to blame. Dutch-process and natural cocoas, although both are unsweetened, are not interchangeable.
Dutch-process cocoa has had alkali added to neutralize its acids; that means it does not react with baking soda. Use it in recipes calling for baking powder, unless there are enough other acidic ingredients to leaven your cake. Some examples of Dutch-process cocoa are Droste, Valrhona and Pernigotti. Most chocolate goods that have a reddish tinge are baked with Dutch-process cocoa.
Natural unsweetened cocoa powder is more acidic and reacts with recipes that also call for baking soda (an alkali). That leavens the baked goods when they hit the heat of the oven. Popular brands include Hershey's, Ghirardelli and Scharffen Berger. Your cocoa should say if it is Dutch-process on the label.