Seimaibuai: The Rice Polishing Ratio

All sake rice is polished before the brewing process starts. After being harvested, dry grains go through a process called seimai. Outer layers of bran, proteins, and lipids are removed. This exposes the shinpaku, the center of the grain, where the starch is concentrated. Removing the grain’s outer layers enhances the sake’s flavor and facilitates the growth of the koji mold necessary for fermentation.

Unpolished brown rice and polished rice.

Seimaibuai (精米歩合) is known in English as Rice Polishing Ratio or RPR. This metric describes the degree to which individual rice grains are polished before being turned into sake. RPR is expressed as a percentage relative to the grain’s original weight.

Sake is categorized based on its RPR. Junmai can have a higher RPR, whereas Honjozo must have an RPR of 70% or lower. Sake with a low RPR often has clean, floral notes and is considered premium quality compared to sake with a high RPR.

Ginjo (吟醸) refers to sake with an RPR of 60% or lower. This means at least 40% of the grain has been polished away, resulting in a more premium taste. Junmai Ginjo is pure Junmai sake with an RPR of 60% or lower, while Ginjo on its own refers to Honjozo sake with an RPR of 60% or lower.

Daiginjo (大吟醸) refers to sake with an RPR of 50% or lower, meaning at least 50% of the grain has been polished away. Junmai Daiginjo is pure Junmai sake with an RPR of 50% or lower, while Daiginjo on its own refers to Honjozo sake with an RPR or 50% or lower.

Knowing how to interpret RPR will help you choose the best sake for your palate. Go forth and enjoy!