N. DOI (1), M. Kobayashi (1), S. Masuda (1), M. Aizawa (1); (1) Asahi Breweries Ltd., Moriya, Japan

Quality
Wednesday, June 4 - 1:00 p.m.-2:45 p.m.
Level 3, Crystal Room

Thiols and sulfides are detrimental components in beer, as they impose unpleasant flavors even when present in trace amounts. Among sulfides, dimethyl trisulfide (DMTS) is a particularly unpleasant component as it imparts the odor of rotten vegetables. We reported at the ASBC Annual Meeting in 2013 that DMTS increases in the whirlpool stage, then decreases during the fermentation process, reaching a few parts per trillion in the finished product, before increasing again during product storage. The amount of DMTS generated within the whirlpool has a high positive correlation with the copper-ion concentration in the wort. However, the amount of DMTS in the wort does not influence the amount of DMTS generated during product storage, suggesting that a precursor of DMTS is generated during fermentation. In the present paper, the mechanism of DMTS formation during the storage of beer is described. To identify the precursor of DMTS generated during product storage, we compared the amounts of DMTS generated after the storage of beer to which various previously identified DMTS precursors were added. We found that the amount of DMTS generated during storage significantly increased after the addition of 1,2-dihydroxy-5-(methylsulfinyl)pentan-3-one (DMTS-P1). The contribution of DMTS-P1 to the rate of DMTS generation after 2 weeks of storage was estimated to be 90%. Moreover, the amount of DMTS generated during product storage increased with increasing DMTS-P1 concentration. These results suggested that DMTS-P1 was likely the principal precursor of the DMTS generated during product storage. Further investigation of the factors influencing DMTS generation revealed that the concentration of DMTS was reduced as the SO₂ concentration increased. As SO₂ is widely known to have anti-oxidizing properties, the possibility that SO₂ suppresses DMTS generation during product storage was examined by adding SO₂ to the product before storage. The analysis confirmed that DMTS formation decreased significantly following the addition of SO₂ compared to control product, suggesting that SO₂ suppresses DMTS generation. SO₂ generation is widely known to occur during the fermentation process, and factors affecting SO₂ formation during the fermentation process have previously been reported. Therefore, the present results suggest that it is possible to suppress DMTS formation by controlling these factors to increase SO₂ formation.

Norio Doi is a researcher in the Research & Development Laboratories for Brewing at Asahi Breweries Ltd. In 2009, he received his M.Eng. degree in polymer chemistry from Kyoto University, where he focused on tissue engineering. Since September 2009, he has worked in the Research & Development Laboratories for Brewing at Asahi Breweries Ltd., primarily in the Department of Flavor and Chemical Analysis.

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