Seimaibuai — The Polishing Ratio and Sake Rice

Seimaibuai (精米歩合) is the proportion of each grain of rice that remains after the outer layers have been milled away, so that a ratio of 60 per cent means that 40 per cent of the grain has been removed. The practice rests on an old observation of the brewing houses: the outer part of the grain carries most of the protein and fat, while the starchy heart is what the koji mould Aspergillus oryzae and the yeast need. Ordinary table rice is milled to roughly 90 per cent, and sake brewers have long milled well beyond that. The figure now stands on the label as a measure of the style and grade, and it is carried by the brewers and the toji, the master brewers, who choose the ratio before the season begins. The special rice, shuzō kōtekimai, is grown for brewing and includes varieties such as Yamada Nishiki, for which Hyōgo is the best known source, and Gohyakumangoku, associated with Niigata and the Hokuriku region.

Brewing rice, Oryza sativa, differs from eating rice in the grain itself: it is larger, with a white opaque core called the shinpaku, a starchy centre with few proteins around it, and it is milled in machines that grind the grain down in long runs, often over a day or more for the finest grades. The ratio is stated as the percentage of grain remaining. Under the sake grading, the ginjō class requires a ratio of 60 per cent or less, and daiginjō 50 per cent or less; the honjōzō grade requires 70 per cent or less, while junmai without further designation carries no minimum on the label. Many brewers mill below these limits, and some go below 30 per cent. A lower figure generally yields a cleaner, more fragrant and lighter sake, with fewer of the heavier flavours of the grain's outer layers; a higher figure leaves a fuller, more rice-forward body. Shimbo treats the ratio as one guide to the style of a sake, to be read together with the category, the rice and the brewery, and not as a ranking of quality on its own.

Highly polished sake, the ginjō and daiginjō styles, is drunk with delicate food whose flavours it must not overwhelm: sashimi of white fish such as red sea bream Pagrus major, chilled tofu, steamed shellfish and lightly dressed vegetables. The structural reason is that a low ratio leaves little of the grain's fat and protein, so the sake is light and aromatic, and it supports a subtle dish where a heavier one would cover it. Sake of a higher ratio, with a fuller body and more acidity, suits grilled fish, simmered dishes in shōyu and mirin, and fried food, where the weight of the sake matches the weight of the plate. Shimbo describes the pairing as one of balance between the intensity of the dish and that of the drink.