Alcohol content of sake
Japanese sake generally sold is undiluted sake adjusted with water to the alcohol content of 15 ~ 16%. However, the alcohol content of squeezed sake mash itself is rather high, at approximately 20~22%, the highest alcohol content among brewed liquor worldwide (wine is between 9~14). While alcohol is generated from sugar broken down by yeast, for yeast to produce large amount of alcohol at once, high sugar content of approximately 40% in the sake mash would be required. However, if the sugar content is too high in the yeast, the production of alcohol would be inhibited due to osmotic pressure. Within high concentration of sugar, yeast cannot grow. Despite this fact, the secret behind the high alcohol-concentration in sake is in the brewing method.
Sake mash that creates Japanese sake is prepared by adding steaming rice, rice malt, and water to the yeast starter with large quantity of cultured yeast. Therefore, sake mash contains two parallel functions: to produce sugar by gradually breaking down steaming rice into glucose using yeast from the rice malt, and alcohol fermentation by breaking down the glucose into alcohol and carbon dioxide gas using the glucose. In other words, the glucose in the sake mash is always maintained at an appropriate concentration for the yeast. For this reason, yeast can generate large quantities of alcohol without exposure to osmotic pressure. In this way, the production of alcohol in the sake mash and alcohol fermentation occurring together is known as “parallel multiple fermentation.” Also, it is known that alcohol tolerance is added to the yeast starter by a portion of the rice malt component, which generates high concentration of alcohol. On the other hand, grapes, the ingredient to produce wine, is a “saccharine food ingredient” that originally contains abundant sugar content, thus there is no need to produce sugar during the production process.
However, in principle, smashing grapes and placing them in a container would allow the natural yeast on the grape skin to produce alcohol fermentation that produces wine. However, the alcohol concentration level will not be as high as Japanese sake. In this way, alcohol fermentation occurring independently is referred to as single fermentation. Also, in case of beer, since the ingredient is the same grain product (starch) as rice, it is necessary to convert the food ingredient into sugar during the production process. First, the saccharogenic amylase of the malt would break down into sugar, where the yeast proliferates for alcohol fermentation. In this way, the function to convert into sugar and alcohol fermentation that takes place independently is referred to as “fermentation after saccharification.” However, since beer uses a large quantity of water, alcohol-level is rather low at approximately 5%.
Sake mash that creates Japanese sake is prepared by adding steaming rice, rice malt, and water to the yeast starter with large quantity of cultured yeast. Therefore, sake mash contains two parallel functions: to produce sugar by gradually breaking down steaming rice into glucose using yeast from the rice malt, and alcohol fermentation by breaking down the glucose into alcohol and carbon dioxide gas using the glucose. In other words, the glucose in the sake mash is always maintained at an appropriate concentration for the yeast. For this reason, yeast can generate large quantities of alcohol without exposure to osmotic pressure. In this way, the production of alcohol in the sake mash and alcohol fermentation occurring together is known as “parallel multiple fermentation.” Also, it is known that alcohol tolerance is added to the yeast starter by a portion of the rice malt component, which generates high concentration of alcohol. On the other hand, grapes, the ingredient to produce wine, is a “saccharine food ingredient” that originally contains abundant sugar content, thus there is no need to produce sugar during the production process.
However, in principle, smashing grapes and placing them in a container would allow the natural yeast on the grape skin to produce alcohol fermentation that produces wine. However, the alcohol concentration level will not be as high as Japanese sake. In this way, alcohol fermentation occurring independently is referred to as single fermentation. Also, in case of beer, since the ingredient is the same grain product (starch) as rice, it is necessary to convert the food ingredient into sugar during the production process. First, the saccharogenic amylase of the malt would break down into sugar, where the yeast proliferates for alcohol fermentation. In this way, the function to convert into sugar and alcohol fermentation that takes place independently is referred to as “fermentation after saccharification.” However, since beer uses a large quantity of water, alcohol-level is rather low at approximately 5%.
日本酒のアルコール度
一般に市販されている日本酒は、原酒を加水調整して15~16%のアルコール濃度に仕上げてあるが、もろみを搾っただけの原酒のアルコール分は高いもので20~22%前後にもなる。これは、世界中の醸造酒の中で最も高いアルコール度数である(ワインは9~14%)。アルコールは酵母が糖分を分解することによって生成されるが、酵母が一度にこれだけ大量のアルコールを造り出すためには、もろみ中に40%近い高濃度の糖分が必要になるという。ところが、酵母は糖分の濃度が高すぎると、その浸透圧のために生理が抑えられてしまう(濃糖圧迫)。ましてや、このような高濃度の糖分の中では、酵母すら生育できない。それにもかかわらず日本酒のアルコール度数が飛び抜けて高い秘密は、その醸造方法にある。日本酒を造るもろみは、酵母を大量培養した酒母に、蒸米と麹、水を添加したものである。したがって、もろみの中では、麹の酵素によって徐々に蒸米がブドウ糖に分解される糖化作用と、その糖分を酵母がアルコールと炭酸ガスに分解するアルコール発酵とが同時進行していることになる。つまり、もろみ中の糖分はつねに酵母にとって適度な濃度に保たれているわけだ。そのため、酵母は濃糖圧迫にさらされることなく、大量のアルコールを生成することができる。このように、もろみの中で糖化作用とアルコール発酵とが同時に行なわれることを「並行複発酵」と呼ぶ。さらに、麹の成分の一部が清酒酵母にアルコール耐性力を付け、高濃度のアルコールを生成することもわかっている。一方、ワインの原料であるブドウは、最初から糖分が豊富に含まれている「糖質原料」であるため、製造工程で糖化の必要が無い。したがって、原理的にはブドウを潰して器に入れておけば、果皮に付着している天然酵母の働きでアルコール発酵だけが行なわれて酒(ワイン)になるわけだが、アルコール濃度は日本酒ほど高くならない。このようにアルコール発酵が単独で行なわれることを「単発酵」という。また、ビールの場合は、原料が米と同じ穀物(でんぷん質原料)なので、製造工程で原料を糖化する必要がある。まず麦芽の糖化酵素によって糖分に分解し、そこに酵母を増殖させてアルコール発酵を行なわせる。このように、糖化作用とアルコール発酵とをそれぞれ単独に行なうことを「単行複発酵」という。しかもビールは水の使用量が多いから、アルコール度数は5%前後と低くなる。