Dutched process cocoa goes through a washing process that neutralizes its acidity. This extra step distinguishes it from natural cocoa powder, which maintains a more acidic quality. Some cooks prefer Dutched, or alkalized, cocoa for its richer color and mellower flavor.
The process of alkalizing, or Dutching, cocoa began in the mid-1800s in Holland as an effort to control the quality of cocoa production. Cocoa is made when the dry remains of cocoa nibs that were pressed to extract the butter are ground into a fine powder. Alkalization occurs when the beans are flushed with a potassium solution before or after pulverization. The washing changes the pH from around a 5 to a 7, which is more neutral. Many name-brand cocoas that you find in the supermarket aren't alkalized; those that are Dutched will say so on the label.
The type of cocoa you use impacts the leavening included in your recipe. Baking soda reacts with acidic ingredients, so it's usually paired with natural cocoa. In red velvet cake, this reaction contributes to the reddish color. Because alkalized cocoa has its acidity neutralized, recipes using it incorporate baking powder, which doesn't require an acidic environment to create the chemical reaction for baked goods to rise.
Alkalized cocoa makes for moister and darker cakes, cookies and muffins. In most cases, you should use the type of cocoa called for in a particular recipe to achieve the best results. If you're in a pinch, substitute natural cocoa powder for alkalized.
If the recipe calls for 3/4 cup or more of cocoa, you may notice that the substitution results in a baked good with a dryer texture and lighter chocolate -- almost fruity -- taste. You cannot substitute alkalized cocoa in baked good recipes that call for natural. If a recipe doesn't specify the type of cocoa to use, look at the leavening called for. Those that include baking soda most likely expect you to use natural cocoa, while those with baking powder only require alkalized.
In recipes in which leavening isn't an issue, such as puddings or drinks, your personal preference determines which type you use. Alkalized cocoa will generally produce a richer, deeper flavor.
Black Cocoa Powder
Heavily dutched cocoa is known as black cocoa powder. It has a bittersweet, but smooth and mellow, flavor with a quite neutral pH of 8. Oreo cookies, for example, are made with black cocoa.