Enhancing the Microbiological Stability of Malt and Beer - A Review

Abstract

While beer provides a very stable microbiological environment, a few niche microorganisms are capable of growth in malt, wort and beer. Growth of mycotoxin‐producing fungi during malting, production of off‐flavours and development of turbidity in the packaged product due to the growth and metabolic activity of wild yeasts, certain lactic acid bacteria (LAB) and anaerobic Gram negative bacteria, impact negatively on beer quality. It follows that any means by which microbial contamination can be reduced or controlled would be of great economic interest to the brewing industry and would serve the public interest. There has been an increasing effort to develop novel approaches to minimal processing, such as the exploitation of inhibitory components natural to raw materials, to enhance the microbiological stability of beer. LAB species, which occur as part of the natural barley microbiota, persist during malting and mashing, and can play a positive role in the beer‐manufacturing process by their contribution to wort bioacidification or the elimination of undesirable microorganisms. Other naturally occurring components of beer that have been valued for their preservative properties are hop compounds. It may be possible to enhance the antimicrobial activities of these compounds during brewing. Some yeast strains produce and excrete extracellular toxins called zymocins, which are lethal to sensitive yeast strains. Yeast strains resistant to zymocins have been constructed. Imparting zymocinogenic activity to brewing yeast would offer a defence against wild yeasts in the brewery. Thus, the antimicrobial properties of naturally occurring components of raw materials can be exploited to enhance the microbial stability of beer.

Effects of Lysozyme on the Microbiological Stability and Organoleptic Properties of Unpasteurized Beer

“…Other bacteria implicated in beer spoilage such as Pediococcus, Megasphaera and Pectinatus 35 were never detected.…”

“…Indeed, LAB can be found in brewing materials at almost every stage of the malting and brewing process, from the standing barley crop to the finished beverage 13,17,28,33 . These bacteria occur as part of the natural barley micro-biota, and persist during malting and mashing 29,35 due to their aero tolerant nature and tolerance of low pH and high ethanol levels.…”

“…Nisin is an effective bactericidal agent against Gram-positive bacteria and spores since it interferes with the cytoplasmic membrane of susceptible species, leading to pore formation, and dissipates the proton motive force 24 . However many Gram-positive bacteria have been shown to be resistant to it, due their ability to synthesize an enzyme, nisinase, which can inactivate the bacteriocin; moreover the cost of nisin addition to all fermentations would be prohibitively expensive 1,35 .…”

“…They exert bacteriostatic effects on most Gram-positive bacteria as they act as proton ionophores and dissipate the transmembrane pH gradient. Several LAB species, such as Lactobacillus spp., have been found to have acquired beer-spoilage ability due to hop resistance genes (horA and horC), and consideration must be given to the fact that altering the hop composition of beer can have a profound impact on the organoleptic and physico-chemical properties of the final product 6,21,22,33,35 .…”

Occurrence of Pectinatus and Megasphaera in the Major UK Breweries

“…Lactobacillus species are found in almost every stage of the brewing process 21,54 . Pectinatus and Megasphaera spp.…”