- Cooling (steamed rice)
The process of air-cooling steamed rice to the target temperature is called horei. When air cools steamed rice, it simultaneously causes its moisture content to evaporate. When water evaporates, it cools the rice still further due to the energy lost through evaporation. The desired-for temperature and the consistency (hard- or softness) of the rice after cooling varies depending on the kind of sake being made, so the cooling time is adjusted as necessary.
In the old days, cooling was carried out naturally by spreading the steamed rice out on hemp mats called mushiro, so cooling was done in the cold of the winter morning. However, apart from the long time necessary for cooling the rice in this way, there were problems with dust and bacterial contamination. Today, there are simple box-like cooling apparatuses and horei-ki (steamed rice cooling machines), which draw air forcibly through the layer of rice to cool it quickly.
In plants which brew year-round, the air used for cooling is de-humidified, sterilized and cooled as the season requires.