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

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.