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

Abstract

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.

Microbial contamination of fuel ethanol fermentations

“…The same effect was observed even with inoculation rates up to 100 : 1 lactobacilli to Saccharomyces. This corresponded to results from other work and caused the authors to state that this low level of chronic contamination was a 'ticking time bomb' for ethanol producers (Magnus et al 1986;Bayrock and Ingledew 2001;Thomas et al 2001). If various fermentation conditions were to change such as pH or temperature, it could allow the lactobacilli to outgrow the Saccharomyces and cause either a loss of final product or a stuck fermentation (Bayrock and Ingledew 2001).…”

“…The same effect was observed even with inoculation rates up to 100 : 1 lactobacilli to Saccharomyces . This corresponded to results from other work and caused the authors to state that this low level of chronic contamination was a ‘ticking time bomb’ for ethanol producers (Magnus et al. 1986; Bayrock and Ingledew 2001; Thomas et al.…”

Acetic Acid Bacteria in Sour Beer Production: Friend or Foe?

“…As AAB are in particular acid- and ethanol-tolerant and not inhibited by hop compounds, they may grow in beer. Beer spoilage by AAB species is characterized by a sour taste and vinegary aroma, caused by ethanol oxidation into acetic acid ( Ingledew, 1979 ; Magnus et al, 1986 ). Besides off-flavor formation, AAB species, such as Acetobacter aceti, Acetobacter liquefaciens , Acetobacter pasteurianus, Acetobacter hansenii and Gluconobacter oxydans , can cause haziness and ropiness in the beer or form pellicles on the beer surface ( Van Vuuren, 1999 ; Van Vuuren and Priest, 2003 ; Briggs et al, 2004 ; Hill, 2015 ; Paradh, 2015 ).…”

Review: Gram Negative Bacteria in Brewing

“…Beer spoilage AAB form a pellicle on the surface with cloudiness in beer containing oxygen. Due to formation of acetic acid, beer tastes sour to vinegary [24] [25]. AAB are strictly aerobic bacteria but some of the AAB isolated from draught beer have been reported to be micro-aerotolerant [26].…”