Yeast
Saccharomyces cerevisiae is the most common yeast
used in breadmaking. Yeast cells metabolize fermentable
sugars (glucose, fructose, sucrose and maltose)
under anaerobic conditions producing carbon dioxide
as a waste product, which acts as a leavening agent and
enhances dough volume. Yeast also supports both gluten
network and aromatic compounds production.
Active cells of yeast are available as a compressed cake
or in dried form. The compressed cake contains
approximately 70% moisture so it is highly perishable
unless it is refrigerated. Active dry yeast is produced by
extruding cake yeast in fine strands, which are dried to
low moisture content. Instant yeast is made from more
active strains of yeast and dried faster and to a lower
level of moisture. Although active dry yeast has a long
shelf-life at room temperature, it must be hydrated
before it is incorporated with other ingredients. In contrast,
instant yeast can be incorporated with flour and
other ingredients without prior hydration