Microbial ecology of cereal fermentations

Cereals are globally number one as food crops as well as substrates for fermentation. Well known products are beer, sake, spirits, malt vinegar, and baked goods made from doughs leavened by yeasts or sourdough. Fermentation processes are enabled by technological measures that act on the metabolically resting grains and direct ecological factors controlling the activity of lactic acid bacteria and yeasts. Fermentable substrates originate from endogenous or added hydrolytic enzyme activities. Examples of their management are malting, koji technology, addition of enzymes from external sources and sourdough, which stands on the origin of all fermentation. When sourdough is continuously propagated under the conditions applied in bakery practice, a stable association of only few species of lactic acid bacteria (LAB) and yeasts achieve dominance and ensure a controlled process. The variation of the ecological parameters acting on the microbial association such as the nature of cereal, temperature, size of inoculum, and length of propagation intervals leads in each case to a characteristic species association, thus explaining that altogether 46 LAB species and 13 yeast species have been identified as sourdough specific.