Closed fermentation (Mippei hakko)

Closed fermentation (mippei hakko) is a method of fermenting alcoholic beverages in a completely sealed environment. In this process, the supply of oxygen that yeast needs to multiply is limited, and fermentation proceeds under anaerobic conditions. Unlike open fermentation, as is the case with sake and similar beverages, the mash does not come into contact with outside air, which makes it possible to control the fermentation temperature and environment more strictly. As a result, it can be easier to produce sake with a distinctive flavor and aroma, and a more stable quality may be achieved. Closed fermentation is often used especially when producing sake with a fruity aroma.