The microbiology of malting and brewing

Abstract

Brewing beer involves microbial activity at every stage, from raw material production and malting to stability in the package. Most of these activities are desirable, as beer is the result of a traditional food fermentation, but others represent threats to the quality of the final product and must be controlled actively through careful management, the daily task of maltsters and brewers globally. This review collates current knowledge relevant to the biology of brewing yeast, fermentation management, and the microbial ecology of beer and brewing.

Fig 1

Microbiota of malting and brewing. The diagram shows an overview of bacterial and fungal species previously reported at all major stages of beer production. (Adapted from reference with permission of the publisher.)

Fig 2

Overview of Saccharomyces metabolic activities influencing beer quality. This simplified schematic summarizes the main metabolic pathways linked to beer flavor modulation by Saccharomyces. βG, β-glycosidase; DMS, dimethyl sulfide; DMSO, dimethyl sulfoxide.

Fig 3

Phylogeny of primary beer spoilage bacteria. The maximum-likelihood tree shows the most common beer spoilage bacteria, colored by ecological niche and taxonomic group. Red, Lactobacillales, isolated primarily from raw materials, fermenting beer, and packaged beer; blue, acetic acid bacteria (Rhodospirillales), limited primarily to spoilage of draft dispensers; green, Enterobacteriaceae, occasional wort contaminants; purple, Veillonellaceae, which cause spoilage in packaged beer.

Fig 4

Schematic overview of main mechanisms of hop toxicity and resistance in Gram-positive bacteria. Iso-α, iso-alpha-acids. Green loops indicate plasmids carrying the hop resistance genes horA and ORF5.