125th Anniversary Review: Microbiological Instability of Beer Caused by Spoilage Bacteria

Abstract

Beer has been generally recognized as a microbiologically stable beverage. However, microbiological incidents occasionally occur in the brewing industry. The microbiological instability of beer is often caused by bacteria consisting of four genera, Lactobacillus, Pediococcus, Pectinatus and Megasphaera. Lactobacillus and Pediococcus belong to the lactic acid bacteria (LAB), whereas Pectinatus and Megasphaera form a group of strict anaerobes that are known as intermediates between Gram‐positive and Gram‐negative bacteria. The frequencies of beer spoilage incidents caused by these four genera have been reported to exceed 90% in Europe and therefore Lactobacillus, Pediococcus, Pectinatus and Megasphaera are considered to be the principal spoilage agents in the brewing industry. Thus, this review consists of three parts involving these four genera. The first part describes spoilage LAB in alcoholic beverages with some emphasis on beer spoilage LAB. In this part, the emergence and evolution of these spoilage LAB is discussed, the insight of which is useful for developing quality control methods for these beverages. The second part is devoted to the hop resistance in beer spoilage LAB. This area of research is evolving rapidly and recent progress in this field is summarized. The third part concerns Pectinatus and Megasphaera. Although this group of beer spoilage bacteria has been described relatively recently, the incident reports in Europe increased in the early 1990s, reaching around 30% of spoilage incidents. Various aspects of Pectinatus and Megasphaera, ranging from their taxonomy and beer spoilage ability to detection and eradication methods are described.

Occurrence of Pectinatus and Megasphaera in the Major UK Breweries

“…Survival of strictly anaerobic bacteria in this aerobic environment can possibly be due to biofilm formation 6,47 . Instruments used in the filling process are prone to formation of biofilms, which are a niche for various beer spoiling microorganisms.…”

“…Pectinatus species are more resistant to acidic pH and can survive at a pH of 4.1 17 . The pH tolerance of these anaerobic bacteria is influenced by the presence of ethanol 47 . Pectinatus and Megasphaera species are tolerant to hop bitter substances and can grow in beer with bitterness ranging between 33-38 EBC bitterness 5,29 .…”

“…It has been reported that Pectinatus and Megasphaera are susceptible to most of the disinfectants used in the breweries such as iodine, chlorine, and formaldehyde 14 . Pectinatus and Megasphaera are easy to control via thermal and disinfectant treatment, but these microorganisms still survive in hard to access corners or in biofilms, which are not easy to access and disinfect 47 .…”

“…Pectinatus can be transmitted to fillers and subsequently to packaged beer via aerosols produced during the filling process 11 and cleaning procedures 20,47 . CO 2 recovery systems are never subjected to cleaning regimes as this involves intensive dismantling of equipment (brewery personal communication), hence the bacteria can prevail in this part of the brewery throughout the year, creating a potential threat to packaged beer products in several ways.…”

“…L. brevis has been implicated in more than half of beer spoilage incidents within the same period 3,6,21 while a further 15-20% have been caused by L. lindneri 2,6 . L. coryniformis, L. casei and L. plantarum are other important Lactobacillus species which have been reported to spoil beer 6,38 with a frequency of beer spoilage incidents of 3, 2 and 1% respectively 2,47,48 . Lactobacillus species cause high turbidity, hazy appearance, unpleasant flavours and a high level of diacetyl in beer 42 .…”