Baker's ammonia, also known as ammonium carbonate, is a leavening agent used in baking. It is a white crystalline powder that releases ammonia gas when heated, which helps baked goods rise. This ingredient is particularly effective in recipes for cookies and crackers, providing a light and crisp texture. Unlike modern baking powders, baker's ammonia does not contain acids or starches, making it a pure form of leavening. It is often favored in traditional recipes, especially in European baking, where it has been used for centuries. However, it should be used in moderation, as excessive amounts can impart an unpleasant taste.