High-Gravity Brewing: Influence of High-Ethanol Beer on the Viability of Contaminating Brewing Bacteria

It has been reported that when high-gravity brewers' worts were supplemented with a source of nitrogen and unsaturated lipids and sterol, ethanol concentrations up to 16.4% v/v could be achieved within normal fermentation times. As the resultant harvested yeast can be repitched over a number of generations, there appears to be no reason in industry to limit the gravities of commercial worts to 16° Plato, especially when the ester and fusel oil patterns of resultant beers may not be as elevated as previously thought. In this report the influence of high-alcohol beer made from 28° P wort on the viability of traditional bacterial brewing contaminants was examined. Lactobacillusand Pediococcus,Acetomonas,Acetobacter,and Zymomonas contaminants were able to survive levels of ethanol of 12-13% v / v . Hafnia (Flavobacterium or Obesumbacterium), Enterobacter (including E. agglomerans), Citrobacter, and Klebsiella species, known to exist through most stages of the fermentation of traditional gravity wort, were completely eliminated by the elevated ethanol levels. Very high gravity fermentations therefore narrow the range of bacteria capable of spoiling the beer, thereby reducing the risk of bacterial spoilage problems. This work illustrates an additional production advantage in favor of increasing original gravities of worts.