Fermented cereals play a significant role in human nutrition in all parts of the world where cereals grow.
These fermentations are started spontaneously or there have been traditional techniques developed in
order to keep starter cultures for these processes alive. With the growing impact of industrial microbiology
during 20th century this traditional starter culture propagation was replaced often, especially in
the dairy industry, by the use of pure, frozen or freeze-dried cultures grown on microbial media. In
contrast to the production of ethanol from cereals, in sourdough a pasteurization step before inoculation
is avoided due to gelatinization of starch and inactivation of endogenous enzymes. Therefore cultures
must be competitive to the relatively high microbial load of the cereal raw materials and well adapted to
the specific ecology determined by the kind of cereal and the process conditions. Less adapted cultures
could be used, but then the process of back-slopping of cultures is limited. Although cereal fermentations
take the biggest volume among fermented foods, only for sourdoughs commercial cultures are available