Sen-mai haisui

Waste water from rice washing

The cloudy effluent created during the brewing processes of rice washing and steeping (shinseki). Washing is carried out to remove rice powder clinging to the surface of the white rice, thereby improving the texture of the rice after steaming. The grains rub against each other during washing to create a mild grinding effect, and this and the original clinging rice powder cloud the water, creating the effluent.

What is more, some components of rice are easily leached out during washing. The most prone to be lost in the water, potassium, is reduced by 30-40% during washing. Sodium, magnesium, phosphorous, saccharides, proteins, amino acids and lipids are all washed out of the rice, so the degree of pollution and turbidity of waste water from this process (defined as BOD (Biochemical Oxygen Demand) and SS (Suspended Solids)) is very high, and is said to account for 90% of the water pollution occurring in a sake brewery.