Water for mashing

Kumi-mizu is the name for the water used when mashing moromi. The ratio of kumi-mizu to the total rice (総米, soumai) used is called the kumi-mizu buai, and is generally around 125-135%, but it is varied according to sei-mai buai, room temperature and the style of sake to be made.

The composition of the water is intimately connected with moromi fermentation, and, generally hard water with high levels of potassium, magnesium、chlorides and so on gives rise to more vigorous fermentation. Soft water low in these minerals is sometimes slightly supplemented. Where a fast fermentation is desirable, the amount of water is increased; on the other hand, fermentation can be slowed by reducing the kumi-mizu buai.

In times when the traditional Japanese system of weights and measures was still in use, the use of one koku (石, 180 L) of water to one koku (石, 150kg) of white rice was called to mizu (“ten water”). Where one koku plus one to (斗: ten to = one koku, so this is 198L, ) was used for the same amount of rice, this was called ju-ichi (long “u”) mizu – “eleven water”. Halfway between the two was known as tourei-han, “ten-and-a-half”. Expressed as kumi-mizu buai , these three become 120%, 132% and 126%.