Studies on acid formation and growth of microorganisms in a continuously operating sourdough fermenter

Abstract

The growth and acid formation of lactic acid bacteria and the growth of yeasts were examined in a specifically designed laboratory fermenter in fermenting sourdoughs under simulated continuous operating conditions. The aim of the investigations was to find the optimal processing conditions for various microorganism florae, which are necessary for the running of a continuously operating sourdough fermenter. The sourdoughs were started from four different sourdough starters and then continually propagated further. Microflorae developed in the sourdoughs which differed considerably from one another, depending on the composition of the original starters. Under constant running conditions, the sourdoughs demonstrated different metabolic activities (rate and degree of acid formation, ratio of lactic to acetic acid). The propagation conditions and the metabolic activity could be altered over a wide range by changing the working parameters, fermentation temperature and mass distribution ratio, for a constant substrate composition (rye flour: ash content, 1%; dough dry solids, 43%). The fermentation temperature exerted the greater influence. The best propagation temperature for the growth and acid formation of the lactic acid bacteria was 35°C and for the growth of the yeasts 30°C. The doubling of the microorganisms necessary for the first stage of the fermentation system under continuous operation could be attained for three of the sourdoughs within a fermentation period of about 3 h at 30°C. On the basis of the results presented, it is possible to optimize the performance of the fermentation system with respect to the growth of the microflorae and the acid formation in dependence on the specific metabolic activities of the microorganisms concerned.