Technical Session 14: Yeast II Session
Takeshi Kawakubo, Company
Co-author(s): Kentaro Iwasaki, Yuichiro Mese, Nobuyuki Hayashi, and Hiroyuki Yoshimoto, Kirin Brewery Company, Japan
ABSTRACT: In 2011, low-malt beer comprised approximately 20% of Japan’s alcohol market. Compared to normal beer wort, low-malt beer wort contains less non-sugar nutrients, such as amino acids, minerals, and vitamins. It has been reported that yeast metabolism is negatively affected by insufficient non-sugar nutrients, thus reducing fermentability and the production of fermentation by-products. To make high quality beer, it is important to control the balance of sugar and non-sugar nutrition concentrations. However, the relationship between the concentration of non-sugar nutrients and yeast metabolism remains unclear. The purpose of this study was to elucidate the relationship between the concentration of non-sugar nutrients, especially vitamins and minerals, and yeast metabolism and their effects on fermentability and beer quality. To investigate the effects of low concentrations of non-sugar nutrients on fermentation and beer flavor, we performed fermentation tests using a synthetic medium or a low-malt beer wort with adjusted concentrations of several minerals and vitamins. As a result, insufficient fermentation and increased pyruvate production above the threshold limit were observed in the fermentation with a low concentration of some minerals and vitamins. This increase in the pyruvate concentration resulted in an unbalanced, acidic flavor. Moreover, this tendency was enhanced with increased repitching. In these experiments, potassium and thiamine concentrations were found to have important roles in yeast fermentation performance. To monitor the physiological state of yeast cropped from this fermentation test, we estimated intracellular metabolite concentrations using capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS). The CE-TOFMS analysis revealed that the organic acid metabolism of this yeast differed from that of normal yeast cropped from all-malt beer fermentation. It is assumed that this difference in yeast metabolism is the cause of the insufficient fermentation and increased pyruvate production. These data suggest that such nutrients as potassium and thiamine have important effects on fermentability and beer flavor, especially during the production of low-malt beer.
Takeshi Kawakubo graduated in 2009 from the Department of Agriculture at Kyoto University in Japan. He began his career in yeast technology development in the Brewing Technology Development Centre at Kirin Brewery Company, Limited.