Illustration of a yeast cell in the process of budding. In this view of the surface of the cell, collar- like outgrowths are seen. These outgrowths are daughter yeast cells being formed in a budding process from the large parent cell. Yeast is a single-celled fungus (Ascomycotina). Budding is a method of asexual reproduction in which a new cell is derived from an outgrowth that becomes detached from the body of the parent. Various stages of outgrowth are seen here. It is this process that enables yeast to reproduce so rapidly when it ferments sugar in the brewing of beer, in wine production, and baking leavened bread.