Control of microbial contamination in continuous primary fermentation by immobilized yeast

Immobilized primary fermentation bioreactors were deliberately contaminated with an enterobacterium, Klebsiella terrigena, and changes were monitored in yeast performance and viability and in chemical composition of the green beers. In addition, the formation of biogenic amines, possible carcinogenic substances, was monitored. K. terrigena caused elevated concentrations of dimethyl sulfide in beer but did not cause significant changes in the concentrations of the analyzed higher alcohols or esters. On the other hand, the ratio between diacetyl and pentanedione was increased. The yeast viability was lowered without observed changes in fermentation capacity. The increased concentration of biogenic amines was mainly due to changes in the cadaverine concentration.