Many sake makers store and polish rice in-house. However, there is a layer of companies in the supply chain of rice who polish and store rice. Some of these companies are owned by farmers. Some are separate. They have the most advanced rice polishing machines and sophisticated warehouses. Whether rice is stored in the brewery or by one of these companies, the temperature and humidity must be precisely controlled to prevent mold from growing, if too wet and warm, but also to prevent rice from drying out and cracking.
After harvesting and drying rice in the field, rice is then husked and stored as “genmai,” unpolished rice, which we consider “brown rice.”
When it’s time to make sake, rice is brought into the first manufacturing section of the brewery. The step of polishing rice, the first step in making sake, is “seimai.” The rice polishing percentage is the “seimai buai” (say-my boo-ay) and the machine that’s used is the “seimai-ki,” “ki” meaning machine.
Rice is evaluated from the time it is received at the brewery until it is used up in the brewing process. Some years, the rice is harder and more brittle, lending it to crack easily. In other years, the rice is softer with higher water content. If sake makers turn up the speed on the “seimaiki” too high and polish the rice too quickly, the rice will crack. The increase in heat will add to this. Thus, they must get a feel for the rice at the beginning of the brewing season and continue monitoring and adjusting.
Polishing also relates to rice varietals. Yamada Nishiki is famous for its flavor and aroma, but sake makers also appreciate its soft composition which makes it conducive to polishing with minimal cracking. Other varietals are known to be harder, requiring more care in this step.
Rice goes through an intensive, meticulous quality grading process. We have already explained this in Growing Rice. Separate from the sake industry organizations who grade quality levels, sake makers further study the rice once it’s in house. This used to be done by eye and by use. Technology can provide highly detailed information down to the field and farmer level.
A rice polishing machine, or “seimaiki,” has a massive chimney that the rice comes shooting down. It is brought back up on a vertical conveyor belt of levels. This is done in a continuous process that can take days to polish one batch.
At the bottom of the chimney is a flat set of stone wheels that are spinning. The rice nicks the top and bounces down the sides, just barely getting nicked.
Although polishing time varies, in general, it takes 24 hours to polish to 60%, ginjo level, and 48 hours to get to 50%, daiginjo level. However, it can take as long as 72 hours to get to 50%.
Nothing is wasted in sake making and rice powder, “nuka” (noo-kah), has many uses. The first brown powder is generally sold as feed for livestock. Finer white powder is used for rice flour or cosmetics.
Rice polishing is stated in terms of how much of the grain is left, not how much is milled away. Until fairly recently, “junmai” had to be polished to 70% or less. Now there is no minimum polishing level for junmai, but honjozo is still 70%. Ginjo and daiginjo have remained 60% and 50%, respectively. Luxury daiginjo will be polished to 40% or 35%, but some sake makers are going lower with sake fans paying more.