Modern brewers rely on a variety of substances to improve beer stability, to insure consistent quality, and to improve appearance and flavor of their product. Corn grits are added to create "adjunct" beers, usually lighter in color and less subject to hazing (reduction in clarity of liquid). Silica gels are also used to reduce hazing, and act as absorbing agents for proteins and polyphenols that cause the cloudiness in chilled beer. Beer carbonation is also sometimes enhanced using pressurized carbon dioxide. Although beer's foaminess is generally a result of the interaction of barley proteins or polypeptides with iso-α acids derived from hops, foam enhancing agents like propylene glycol alginate (PGA) may also be added. This chapter from a book on beer quality focuses on the study of beer foam properties.