The foamy residue on the inside of a glass is called Belgian lace. Belgian lace (also called Brussels lace) is the foamy residue of a beer’s head that clinks to the inside of the glass when the beer is drunk. Its presence is a sign of a well-made beer with good head retention. It does not signify a more alcoholic beer as the term “legs” does with wine. Often confused with grist, grist is the combination of malts prepared for milling during the beer-making process and the origin of the expression “grist for the mill”.