Thomson, E.1, Bergsveinson, J.2, Mortimer, G.1, Jacoby, D.3, Coady, Y.3 and Ziola, B. R.4, (1)Phillips Brewing & Malting Co., Victoria, BC, CANADA, (2)University of Regina, Regina, SK, CANADA, (3)University of Victoria, Victoria, BC, CANADA, (4)University of Saskatchewan, Saskatoon, SK, CANADA
Technical Session 8: Microbiology
Wednesday, June 07, 2017
8:15–10:00 a.m.
Harbourview (1st Floor)
Strictly anaerobic beer spoiling bacteria are generally believed to have gained a foothold in the industry as a result of technological advances in anaerobic filling in the 1980s. Among these organisms, Megasphaera cerevisiae produces particularly offensive off-flavors, including butyric acid, but no literature exists to demonstrate its growth in beer containing greater than 4% ethanol. This study explores the genomic and physiological traits underpinning the ability of a canning line isolate of M. cerevisiae to grow in beer containing up to 5% ethanol—the first known case of this organism documented to grow above 4% ethanol. Using polymerase chain reaction (PCR) and specialized microbiological methods, M. cerevisiae strain NSB1 was identified and isolated from the underlid CO2 injector of a brewery canning line. Whole genome sequencing was carried out, and data were analyzed against the only previously sequenced M. cerevisiae strain, which is not known to grow above 4% ethanol. Initial isolation of the bacteria was carried out on Wallerstein differential agar. Growth experiments were carried out in beer containing varying ethanol concentrations and pH levels, as well as in modified de Man, Rogosa and Sharpe media containing ethanol and adjusted to pH 4.6. All cultures were grown and maintained anaerobically. NSB1 demonstrated strong growth in beer containing up to 5% ethanol above pH 4.5, accompanied by copious off-flavor production. Genomic sequencing of NSB1 indicated a diverse set of potential mechanisms by which the strain thrives in elevated ethanol concentrations, including genes encoding a variety of efflux pumps and alcohol dehydrogenase not present in the previously sequenced reference strain that has not demonstrated growth above 4% ethanol. In addition, the presence of several sets of glycerol degradation pathways suggests a previously unidentified energy source for M. cerevisiae during growth in beer. Eradication of the biofilm housing the bacteria was carried out using sequential applications of hot sodium hydroxide, nitric acid and acidic hydrogen peroxide. Using PCR of surface swabs and packaged products, the elimination of the bacterial population was confirmed. These results demonstrate the urgency for increased vigilance toward these bacteria, which contrary to conventional wisdom may be capable of growth in regular strength beer, and suggest a need for improved tools for the detection and identification of bacteria requiring specialized growth conditions.
Euan Thomson manages the Quality, Research, and Malting Departments at Phillips Brewing & Malting Co. in Victoria, Canada. During his three years at the brewery, he has introduced new methods for the molecular detection of various bacteria and wild yeast over a range of brewery process steps and established research partnerships with local scientists to explore yeast physiology and epigenetics, barley polyphenols, packaging material contaminants, aging markers in whisky, methods for hop oil emulsification, and chemical analysis methods for beer and raw materials. He has a Ph.D. degree in microbiology and spends his free time exploring the Vancouver Island backcountry, playing music and helping to build the island community.
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