Generally Recognized as Safe (GRAS) organism. Fermentation Sake fermentation is a three-step process called . The first step, called , involves steamed rice, water, and being added to the yeast starter called : a mixture of steamed rice, water, kōji, and yeast. This mixture becomes known as the (the main mash during sake fermentation). The high yeast content of the promotes the fermentation of the . On the second day, the mixture stands for a day to let the yeast multiply. The second step (the third day of the process), called , involves the addition of a second batch of , steamed rice, and water to the mixture. On the fourth day of the fermentation, the third step of the process, called , takes place. Here, the third and final batch of kōji, steamed rice, and water is added to the mixture to complete the three-step process. The fermentation process of sake is a multiple parallel fermentation unique to sake. Multiple parallel fermentation is the conversion of starch into glucose followed by immediate conversion into alcohol. This process distinguishes sake from other liquors like beer because it occurs in a single vat, whereas with beer, for instance, starch-to-glucose conversion and glucose-to-alcohol conversion occur in separate vats. The breakdown of starch into glucose is caused by the fungus, while the conversion of glucose into alcohol is caused by yeast. Due to the yeast being available as soon as the glucose is produced, the conversion of glucose to alcohol is very efficient in sake brewing. This results in sake having a generally higher alcohol content than other types of liquor. After the fermentation process is complete, the fermented is pressed to remove the sake lees and then pasteurized and filtered for color. The sake is then stored in bottles under cold conditions (see "Maturation" below). The process of making sake can range from 60–90 days (2–3 months), while the fermentation alone can take two weeks. On the other hand, ginjō-shu takes about 30 days for fermentation alone. Maturation Like other brewed beverages, sake tends to benefit from a period of storage. Nine to twelve months are required for the sake to mature. Maturation is caused by physical and chemical factors such as oxygen supply, the broad application of external heat, nitrogen oxides, aldehydes, and amino acids, among other unknown factors. is the job title of the sake brewer. There are various theories