| Summary: | 碩士 === 國立中興大學 === 食品科學系 === 92 === Sake, a traditional alcohol in Japan, is a kind of rice wine which is made from polished rice, rice-koji, yeast starter (called moto) and water. In sake brewing, both saccharification and fermentation proceed simultaneously in the fermented mash(called moromi) at low temperature.The moromi is then pressed, filtered, followed by blending and pasteurization. The alcohol content of sake is about 18 %(v/v). The objectives of this study included screening of a yeast strain for optimal moto-making, establishment of the optimal condition of koji-making, evaluation of using other varieties of rice, and possibility of changing the proportions of water and koji used in the original formula for optimal sake brewing. In addition, feasibility of using active dry yeast as starter in sake brewing was also investigated.
The yeast Saccharomyces cerevisiae CCRC 21679 was chosen for its best alcohol producing capability, up to 14.12 %. Soaking of various rice with water at 15℃ or 25℃, the moisture content of Tainung 71 after soaking for 12 hours were 27.67 % and 27.11 %, respectively. The moisture content of Tai-sen 10 after soaking for 11 hours were 28.67 % and 28.93 %, respectively. The moisture content of Tai-keng 8 after 12 hours were 27. 76 % and 29.05 %, respectively.
After the rice was steamed, the koji-making was performed. When the moisture content of Tainung 71 was 41.78 %, the koji had the highest amylase activity at 296.68 U/g, and acidic protease at 113.20 U/g. The amylase activity was 174 U/g, and acidic protease was 89.78 U/g when the moisture content of Tai-sen 10 was 45.21 %. Similarly, when the moisture content of Tai-keng 8 was 38.67 %, the amylase activity with 272.67 U/g, and acidic protease with 93.25U/g.
Addition of wooden ash at 1.0 % or 1.5 % to the steamed rice of Tai-keng 8 or Tai-sen 10 enhanced the sporulation of Aspergillus oryzae CCRC 32279 of spores grown on the product ( called seed koji ) were about 107 per gram. The seed koji was then used as starter to prepare koji, the inoculum size at 1.0 % ( w/w ) was optimal.
The final ethanol concentration was 16.58 % if a commercial active dry yeast was used as starter, while the final viable cell counts were 1.82 × 107 cfu/ml. Two varieties of rice, Tai-keng 8 and Tai-sen 10, were used as raw materials for sake brewing using S.cerevisiae CCRC 21679 as starter, the final ethanol concentrations were 18.2 % and 17.6 %, respectively. Finally, the proportions of water and koji used in the original formula for optimal sake brewing were re-evaluated. Higher ethanol concentrations could be obtained when ratio of water or koji to the overall weight of steamed rice used in the mash were 124 % and 35 %, respectively.
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