Yeast fermentation. Froth produced by Baker's or Brewer's yeast Saccharomyces cerevisiae, in the process of fermenting sugar. Yeast, a form of fungus, multiplies rapidly by a process of budding or by fission. It has the ability to ferment sugars and in so doing produces alcohol and carbon dioxide (seen here as bubbles). These properties are used in the production of wines, beers, and in the baking of leavened bread, cake and pastry.