ビール製造への利用を目的とした香気生産野生酵母の香気特性および実用性評価に関する研究 Study on Characterization and Utility Evaluation of Flavor-producing Wild Yeast for Beer Production

In the thousand year history of beer brewing, many innovative events have taken place. It can be said that most of the events happened through the development of new technology regarding yeasts or the discovery of a novel strain of yeasts itself. At the present time, nearly all craft beer companies have to continuously develop new beers in order to gain more of the market share.　In this thesis, to produce a characteristic craft beer, at first five different tree saps were collected from the Ise-shima area and each sap was mixed into each pasteurized wort containing hops in a sterilized Erlenmeyer flask. After mixing, the flasks were placed in a dark at 30˚C for 2 days. Some worts produced an aromatic alcohol flavor and small frothy barms. One wort with superior flavors was propagated in a stock pot filled with pasteurized wort. And after 2 days, propagated wort was utilized to brew 1000 liters of beer. After one year, the second brewing was attempted by using sediment of a fermentation tank that had been used for the first brewing.　Next, a flavor-producing wild yeast was isolated using an enriched culture method from sediment of a fermentation tank for the second brewing. A comparative analysis of the sequences of ITS1-5.8S rDNA-ITS2 region indicated that the isolated strain was related to Sacchromyces cerevisiae and was named KADOYA1. To evaluate the characteristic and utility of KADOYA1, a commercial scale (1,000 L) of beer production test was performed using ale beer yeast strain 1056 and 3068 as a control. The fermentation rate of KADOYA1 was slightly lower than those of strains 1056 and 3068, but ethanol production was sufficient. The odor properties of beer brewed with each yeast strain were estimated with quantification of gas chromatography-mass spectrometry, and a fragrance evaluation was performed using an electronic noses (FF-2A). The results showed that the beer brewed with KADOYA1 has a characteristic odor that is different from those of the beers brewed with the other two strains. KADOYA1 was deemed to be a commercially useful yeast for craft beer production because it has sufficient fermentation and good flavor-producing abilities. KADOYA1 is expected to be used to produce craft beer with a unique flavor.

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