Sake and Beer Spoilage Lactic Acid Bacteria - A Review

Abstract

Japanese rice wine, sake, is a traditional alcoholic beverage in Japan. Similar to the case with beer, sake is known to be microbiologically stable and most microorganisms fail to grow in sake. This is principally due to its high ethanol concentration that reaches approximately 20% (v/v) in undiluted sake products and 15% (v/v) in finished products. Despite the high level of ethanol content, spoilage incidents occasionally occur in sake, due to the presence of highly ethanol-tolerant lactobacilli, known as hiochi-bacteria. Hiochi-bacteria are generally composed of two groups of lactobacilli, hiochi-lactobacilli and true hiochi-bacilli. The former group of lactobacilli is less ethanol-and heat-tolerant, and therefore rarely poses a problem to sake products. In contrast, the true hiochi-bacilli exhibit extraordinarily high ethanol tolerance and cause spoilage incidents in sake, conferring acidity and off-flavors, such as diacetyl, in spoiled products. From a taxonomic standpoint, the true hiochi-bacilli mainly consist of two Lactobacillus species, L. fructivorans and L. homohiochi. The strains of true hiochi-bacilli prefer sake-like environments, and the presence of ethanol and mevalonic acid, in combination with low pH milieu, is essential or stimulatory for the growth of these bacteria. Interestingly, the type strain of L. fructivorans does not show such characteristics, suggesting the true hiochi-bacilli are profoundly adapted to sake environments. Although beer spoilage lactic acid bacteria do not have close taxonomic relationships with true hiochi-bacilli, there are striking similarities between these two groups of spoilage lactic acid bacteria. In this review, unique features of sake and beer spoilage lactic acid bacteria are discussed in comparative terms.