Journal of the Brewing Society of Japan; Vol.19, No.9, 1996 saki4.txt "Kyokai Yeast No.15 for Japanese Sake "Akita-ryu Hana-kobo" Akita Research Institute of Food & Brewing Kyuichi SAITO 1. Characteristics of Akita kobo, yeast The yeast, "Akita-ryu Hana-kobo" AK-1, developed by the Akita Institute of Brewing, is considered to have a close relationship with Kyokai Yeast No.7. Three reasons for this belief are the red hue under the T.T.C. coloring method, that it did not increase on a beta-alanyn medium, and the pattern of electrophoresis. Consideration has been given, however, that it might be a mutation of the Kyokai Yeast No.7 because its characteristics are different, such as strong fermentation power and saccharifying of maltose, weak power of saccharifying of alpha-methyl gulcosid and high productivity of capronic acid ethyl. Because of its advantages such as no bubble generation, high production of the of fragrance of fatty acid ethyl ester, and remarkably low production of organic acids, it is suitable for low-temperature and long-term fermentation. 2. Basic concept of ginjo-shu brewing A special brewing method is necessary to produce the "Akita-ryu Hana-kobo" yeast from which the delicate ginjo-shu with its strong initial taste and light aftertaste is made. The results of studying brewing using this yeast have shown that the following operation is suitable. An example is shown in the table below; -Shubo1st addition2nd addition Final additionWater additionAlcohol additionTotal Rice(kg)45120 225360-- 750 Steamed rice(kg)3090 180 300--600 Koji(kg)1530 45 60--150 Water(l)50 130310 530(100)- 1,020 30% brewery's alcohol(l)----- 200200 3. Material process It is important to use rice having a low albumin content and low ratio of non-usable rice, by measuring the ratio of usable rice during the polishing process. Preliminary testing is necessary before the rice is soaked in water. The ratio of water in the rice should be a little high, from 29 to 30 %. After the rice is steamed, any additional water should be removed as soon as possible. When the rice steaming is completed, any steam remaining on the surface of the rice should be removed by dry steam. The rice should then be kept in ways that no more water evaporates. The ratio of water contained in rice should be controlled at from 40 to 43 %. to make the rice suitable for koji rice, having a hard surface but soft inside. 4. Koji rice process After carrying steamed rice into the Koji Muro, a sauna-like warm room, to produce koji rice, the steamed rice should be spread as thin as possible, over the "Toko", wooden table. Dried koji spores are scattered over the surface of the rice. The amount of dried koji spores spread over 100 kgs of rice should be, as a standard, 20 grams for Shubo and the 1st addition, and 10 grams for the 2nd and the final addition. The most careful attention should be paid to scattering the dried koji spores, because the way of scattering decides the final quality of the koji rice. As an example of koji rice making under the standard conditions above, using steamed rice cooled to 32oC from 70oC just after steaming, the final koji rice for the final addition is ready 50 hours after the process began. Afterwards, each two hours later, koji rice for the 2nd addition and the 1st addition is obtained, respectively. Finally, koji rice for shubo is obtained 56 hours after the process began. The important part of the "Mori" process, stacking the koji rice that is moved from the wooden table in shallow wooden boxes, is to stack the same amount as evenly as possible, at the appointed time without regard for the degree of growth of the koji rice, and to keep surface temperature at not more than 30oC after stacking. The "Naka-shigoto", middle processing, is to slightly evaporate the water on the surface of the koji rice while maintaining the temperature of the koji rice. The "Shimai-shigoto", final processing, is to fully evaporate any water on the surface of the koji rice in order to prevent excess growth. The maximum temperature should be 42oC. The waiting time for the koji rice should be 14 to 16 hours for the first addition and 10 to 12 hours for the second and the final addition after temperature decreases to 40oC. It is necessary to take time, because glucose amirase is produced during this time. Before the koji rice is shipped from the room, 2 to 3 hours of drying is recommended. This drying is said to improve the fragrance of the final mash. 5. Shubo, starter mash The first objective of this process is to grow a pure lot of shubo, starter mash, which can produce a rich ginjo fragrance. Therefore, more than two 2 liters of activated cultivated-yeast is used per 100 kgs of rice. The purity of the starter mash is maintained by the addition of only 400 to 500 ml of lactic acid. The temperature of the process is 18oC. The target of the maximum specific gravity is 14 to 15 degrees, measured by a Baume meter on the sixth day from the beginning. After 14 days, the shubo is ready. Adequate data for use is a specific gravity of 4 to 5 degrees as measured by a Baume meter, acidity of 4.5 to 5, and alcohol content of 10% to 11%. As a result of the "Sokujo-ho", quick fermentation method, starter mash is available to use 14 days after the process is started. 6. "Moromi", final mash "Akita-ryu Hana-kobo" is a type that does not generate bubbles during fermentation. Therefore, judgment based on the appearance of the surface of the final mash during the process is difficult. The process management should be based on the B.M.D. curve by analyzing the mash from time to time. The accumulation of production data is also important. This should contribute to further success in brewing ginjo-shu in the future. In this process, the temperature at each addition stage is important. Particular attention should be paid to the temperature during the final addition, because the final mash making actually starts after the final addition. One hour before each addition stage, water and koji rice are mixed before the addition, in order to obtain enzyme-rich water. The temperature at the first addition should be 11 to 12oC. The temperature during the second day, when addition is not done, should be 11.5 to 12.5oC, the same as or about 1oC higher than that of the 1st addition. Attention should be paid to not decrease the temperature. The acidity will be 1.7 to 2.0, and the specific gravity will be 8 to 10 as measured by a Baume meter. The temperature of the second addition should be 7 to 8oC. Particular attention should be paid that the temperature of the final addition is not below 6oC. Again, most careful attention should be paid to the control of the temperature at each stage, because control has a major influence on the process that follows. In the first half of this process, the temperature rise should be slow, about 0.5oC a day, because this is necessary so as to control the degree to which the rice becomes sugar and the extent of acid generation. The temperature should be controlled to reach its highest, 10oC, on the ninth day. This is very important. If the temperature rise is restricted too much, however, a dangerous situation such as cooling down may occur. The target maximum specific gravity is 6.5 degrees. In the last half of this process, the temperature of the final mash should be controlled according to the number of days passed. It should be noted that a temperature decrease of more than 1oC in "Akita-ryu Hana-kobo" yeast weakens the fermentation. The target of control in this process is the enzyme reaction to produce the ginjo fragrance. The fragrance can easily evaporate, however, and it is important that the process temperature should be kept low to prevent such evaporation. Therefore, all reactions including in the brewing process are slow and require a long time. As an example of this process, fermentation is usually completed 33days after the final addition. Therefore, the target of this process is 33 to 35 days. 7. Alcohol addition When the sake fermentation process is completed, alcohol is added. The amount of added alcohol depends on the final mash, usually 60 to 90 liters per ton of the final mash. The brewery's alcohol density is normally 30%. Before addition, the alcohol should be kept at the same temperature as that of the final mash. The addition should be done slowly, with sufficient mixing after the addition. The mixture should be filtered about four hours after the addition. An example of the process is shown below. Alcohol(%)Japanese Sake ValueAcidity Amino Acidity(ppm) Isoamylacetate(ppm)Isoamyl alcohol(ppm) Hexanoic acidethyl esterE/ARatio Ratio of sake lees(%)Alcohol gain(l/ton) 17.5+5.01.3 0.84.0125 4.43.358.2 278.1 Conclusion A brief outline of brewing ginjo-shu by using "Akita-ryu Hana-kobo" yeast is described above. However, if adequate storage and aging are not done afterward, all the work done so far is for naught. After filtering, management of the mix is as important as that of the brewing process.