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Brewing yeasts have an essential role in beer production as they convert sugar into ethanol and carbon dioxide and impart flavor to beer during brewing. Brewing yeasts can be classified into the following two types: ale yeast (or top-fermenting yeast; Saccharomyces cerevisiae), which is used for ale-type beer production; lager yeast (or bottom-fermenting yeast; Saccharomyces pastorianus), which is used for lager-type beer production. Globally, approximately 90% of beer is produced using lager yeast. The entire genomes of S. cerevisiae S288C and S. pastorianus Weihenstephan 34/70 were sequenced in 1996 and 2009, respectively. Saccharomyces eubayanus, a parent strain of the lager yeast, was discovered in 2011. These advances have markedly contributed to the studies on brewing characteristics and brewing yeast genes and the rapid development of the field of yeast genetics. To contribute to the development of the beer industry, this review summarizes the genetics of brewer's yeast with a special focus on its genomic structure and the genes involved in brewing characteristics. [ABSTRACT FROM AUTHOR]

2-Mercapto-3-methyl-1-butanol (2M3MB) imparts an onion-like off-flavor to beer and is known to be formed from 2,3-epoxy-3-methylbutanal (EMB), which is generated in the reaction of iso-alpha acids with oxygen during the hot aeration of brewer's wort. Our previous results revealed that 2-mercapto-3-hydroxy-3-methylbutanal (2M3H3MB), formed from EMB by a nonenzymatic reaction with hydrogen sulfide, serves as the intermediate to 2M3MB. However, little is known regarding the 2M3H3MB to 2M3MB conversion process. In the present study, preparative column chromatography coupled with an enzyme assay revealed that two enzymes of Saccharomyces pastorianus, Old Yellow Enzyme 2 (Oye2p) and alcohol dehydrogenase 6 (Adh6p), are involved in the conversion process. An in vitro reaction containing these enzymes purified from recombinant Escherichia coli cells converted 2M3H3MB to 2M3MB. Furthermore, a yeast mutant with deletion of the genes encoding these two enzymes dramatically decreased 2M3MB formation. Our series of studies has therefore revealed the overall mechanism of 2M3MB formation starting from EMB through 2M3MB. [ABSTRACT FROM AUTHOR]

Fermentation profiles of four different yeasts reportedly defective in sucrose utilization indicate that all strains tested removed particular sugar via selective conversion to ethanol in a saccharide mixture. At the temperature of pressed sugarcane juice, Saccharomyces dairenensis and Saccharomyces transvaalensis performed better in ethanol production rate and yield, respectively. [Copyright &y& Elsevier]

High-gravity brewing has been used to reduce costs and energy, as well as to produce new types of beer with high alcohol content. To identify the key metabolic pathways underlying efficient high-gravity brewing, we explored metabolites that were highly accumulated during alcoholic fermentation under high-maltose conditions using bottom-fermenting brewer's yeast, Saccharomyces pastorianus. Based on metabolomic data, we focused on S -adenosylmethionine (SAM), which may be involved in glycolysis and alcoholic fermentation in the closely related yeast species Saccharomyces cerevisiae. Exogenous SAM led to an increase in fermentation rate in both high-maltose synthetic medium and high-gravity wort. Although SAM is composed of methionine and the adenosine moiety of ATP, neither methionine nor adenosine significantly increased the fermentation rate. These results suggest that SAM is specifically associated with the fermentation rate of bottom-fermenting brewer's yeast. Deletion of the adenosine kinase gene ADO1 , which leads to an accumulation of SAM in S. cerevisiae cells, elevated the fermentation rate in high-glucose synthetic medium at 15°C; however, this ado1 Δ effect became less significant at higher temperatures. Similarly, a SAM-accumulating S. pastorianus mutant strain, with enhanced resistance to the adenosine analog cordycepin, exhibited a higher fermentation rate in both high-maltose synthetic medium and high-gravity wort. Taken together, our study demonstrates that SAM acts as a positive regulator in high-gravity brewing at low temperatures and that cordycepin resistance could serve as a useful indicator for breeding S. pastorianus strains with high fermentation performance. [ABSTRACT FROM AUTHOR]