Sake brewing characteristics of yeasts isolated from flowers by an enrichment culture method

Abstract

In our previous papers, we reported on isolated ND-4 and HNG-5 strains which have the characteristics of sake yeast from natural flowers using a synthetic medium containing yeastcidin produced by Aspergillus oryzae No.G. The ND-4 strain produced a high concentration of ethyl caproate and the HNG-5 strain produced a high concentration of ethyl caproate and isoamyl acetate in fermented sake moromi. This time, we isolated a new type of strains NI-2 and BK-1 from natural flowers using a synthetic medium containing yeastcidin. Results of examining its physiological character showed them to be non-forming sake yeast types.
These four strains were used in sake brewing tests on a small scale. Analysis of the aroma of these sake tested four strains.
The test brewing sake used the NI-2 strain which contained ethyl caproate and isoamyl acetate at a sufficient balance. The NI-2 strain possessed aroma components nearest the HNG-5 strain. The test brewing sake using the BK-1 strain produced a high concentration of isoamyl acetate. On the other hand, the test brewing sake using the ND-4 strain had high amino acid. As compared with the K-9 strain, the alcoholic tolerance of ND-4 strain was weak. We examined the effect of fermentation temperature on the synthetic medium for ethyl caproate synthetic ability. The ND-4 strain showed high ethyl caproate formation ability at 13 to 15°C in the synthetic medium. From the above results, these four strains yielded their respective qualities in a sensory test by skilled panelists and the aromatics characteristic of the test brewing sake.