After polishing the rice, the next step in the sake making is process is washing and soaking. Washing is simple enough (if you have a nice little washer like they have here); the rice is washed in 10 kg portions for 1 min, dropped into a bag, rinsed gently for 30 sec, and is then placed into a container full of water to soak.
But how long should the rice be soaked for?
For rice to be used in making koji, the target amount of water to absorb is approximately 33% of the dry weight. For rice to be added into the fermentation directly(after steaming- called “kake mai”), the rice should absorb a little less water, around 29%. In the photo, Uei-san is writing down the times that rice should be placed in, and taken out of, the soaking containers. For the first bag, there is a little trial and error, with the rice being soaked, then weighed (after removing excess external water), then placed back in the water, then weighed again. For this batch of rice, which was called “Hinohikari” and was milled to 60%, it took 11 min 15 sec to soak up 29% the initial weight of water. Hope that helps answer the question!