Which component can be used to enhance the volume of whipped egg whites, besides cream of tartar?

Bicarbonate of soda, also known as baking soda, can improve the aeration and stability of whipped egg whites. When added to egg whites while beating them, it raises the pH level and helps to create a more alkaline environment. This change enhances the protein structure of the egg whites, resulting in increased volume and a more stable foam. This stability is crucial for recipes that rely on whipped egg whites as a key component, such as meringues and soufflés.

In contrast, other ingredients like butter, whipped cream, and cream cheese do not serve the same purpose. Butter would introduce fat into the mixture, which can inhibit the formation of a good foam. Whipped cream is a product that already contains fat and does not provide the necessary structural support for egg whites. Cream cheese is dense and fatty, making it unsuitable for enhancing the volume of whipped egg whites. Thus, using bicarbonate of soda is the best choice for achieving increased volume and stability in whipped egg whites.