What Is Seimaibuai? The One Number on Every Sake Label
Seimaibuai (精米歩合) is the rice polishing ratio: the percentage of each rice grain that remains after its outer layers have been milled away. A seimaibuai of 60% means 40% of the grain has been ground off and 60% is left to brew with. The number is printed on almost every bottle of premium sake, and it points in the opposite direction to what most people expect — a lower figure means more polishing, not less.
If you have ever picked up a bottle labelled “seimaibuai 50%” and assumed it was only half-milled, you are in good company. It is the single most misread number in the sake world. Once you understand what it measures and what it does not, the rest of the label starts to make sense.
What does seimaibuai actually measure?
Seimaibuai measures how much of the rice grain survives milling. It is the weight of the polished white rice divided by the weight of the original brown rice, expressed as a percentage.
Brewers do not use the same rice you eat with dinner. Before fermentation, sake rice is milled — literally ground down on abrasive rollers — to remove the outer part of each grain. If a brewery starts with 100 kilograms of brown rice and polishes it until 60 kilograms remain, the seimaibuai is 60%. The other 40% has become rice powder, sold on for crackers, miso, and other foods.
So the number describes what is left, not what is taken away. That framing is the source of nearly every misunderstanding.
Why does a lower number mean more polished rice?
A lower seimaibuai means more of the grain has been removed, because the number counts what remains. It runs against intuition, so it is worth stating plainly. Think of it as a countdown rather than a score:
- 90% — barely milled; 10% removed. Common in everyday table sake.
- 70% — a light polish; the threshold for honjozo-grade sake.
- 60% — noticeably milled; the ginjo threshold.
- 50% — heavily milled; the daiginjo threshold.
- 35% or below — the grain reduced to roughly its centre; rare and labour-intensive.
The smaller the number, the smaller — and more polished — the grain that goes into the tank. A “seimaibuai 35%” sake has had almost two-thirds of every grain ground away before brewing even begins.
What does polishing actually remove, and why does it change the flavour?
Polishing strips away the outer layers of the grain, which are richer in protein, fats, and minerals than the starchy core. Removing them tends to produce a cleaner, more aromatic sake.
A grain of rice is not uniform. Its centre — the shinpaku, or “white heart” — is dense with the starch that yeast and koji convert into sugar and then alcohol. The outer layers carry most of the grain’s protein, lipids, and minerals. During fermentation those compounds break down into amino acids and other molecules that add body, savouriness, and sometimes heavier or rougher flavours.
Mill more of the outside away and you brew with a purer parcel of starch. The result generally leans lighter, cleaner, and more fragrant. Leave more of the grain intact and you tend to get a fuller, more savoury, rice-forward style. Neither is a flaw; they are different destinations. We unpack the mechanics in more detail in the science of polishing.
What seimaibuai do you need for ginjo, daiginjo, and honjozo?
Japan’s special-designation categories (tokutei meishoshu) set maximum polishing ratios. To carry a name, a sake must be milled at least to the listed figure — the seimaibuai must be that number or lower.
| Designation | Maximum seimaibuai | Added alcohol? |
|---|---|---|
| Honjozo | 70% or lower | Small amount |
| Ginjo | 60% or lower | Small amount |
| Daiginjo | 50% or lower | Small amount |
| Junmai Ginjo | 60% or lower | None |
| Junmai Daiginjo | 50% or lower | None |
| Tokubetsu (Junmai / Honjozo) | 60% or lower, or a special method | Depends on type |
These thresholds come from the National Tax Agency’s labelling standards (in Japanese). One important caveat: for ginjo and daiginjo, polishing is necessary but not sufficient. The rules also require ginjo-zukuri — a slow, low-temperature ferment that develops the category’s signature fruity, floral aromatics. A sake milled to 50% that was not brewed in the ginjo style cannot call itself daiginjo. If you want the full map of how these names relate, see our guide to junmai, ginjo, and daiginjo.
Does junmai have a required seimaibuai?
No. Junmai has had no minimum polishing ratio since 1 January 2004. This surprises a lot of English-language guides, many of which still repeat an old “70%” rule.
Until then, junmai-shu had to be milled to 70% or lower to use the name. The National Tax Agency removed that requirement, reasoning that improvements in milling and brewing equipment meant polishing ratio alone no longer captured quality. The change was also nudged along by the popularity of “rice-only” sake products that had appeared in the late 1990s. In the same revision, the rules added a different condition: junmai must be made with koji rice equal to at least 15% of the total white rice weight.
So today a junmai can be milled to 80%, 70%, or 50% and still be a junmai. Producers are required to print the actual seimaibuai on the label, which means the number is still there for you to read — it just no longer gates the name.
Is a lower seimaibuai always better?
A lower seimaibuai is not automatically better. It signals more milling, more labour, and usually a lighter, cleaner style — but “cleaner” is a direction, not a verdict.
Polishing ratio is one of the few sake facts that comes as a hard number, so it is tempting to read it like a test score: higher polish, higher marks. It doesn’t work that way. Grinding away more of the grain removes the very compounds that give some sake its depth and savour. A junmai milled to 70% can be more interesting with food than a daiginjo milled to 35% — it simply aims at a different flavour. The number tells you about style and effort. It does not tell you what you will enjoy.
There is also a cost dimension. Deep polishing is slow, wastes a large share of the harvest, and demands premium rice that can survive heavy milling without shattering. That effort is real, and it shows up in the price. But paying for a lower number is paying for a style and a degree of craftsmanship, not for a guarantee that the sake in the glass suits your palate or your dinner.
Frequently asked questions
Is seimaibuai the same as seimai buai?
Yes. “Seimaibuai” and “seimai buai” are just two romanised spellings of the same Japanese word, 精米歩合. You will also see it translated as “rice polishing ratio,” “rice polishing rate,” or “milling rate.” They all mean the same figure.
Does a seimaibuai of 50% mean the rice is half milled?
Yes — 50% means half of each grain has been polished away and half remains. It is the threshold for daiginjo and junmai daiginjo. Because the number counts what is left, “more milled” always shows up as a smaller figure.
What is the lowest seimaibuai possible?
A handful of breweries have pushed below 10%, polishing away more than 90% of each grain, though such releases are rare and expensive. There is no legal floor; the practical limit is how much milling the rice can take before it breaks apart.
Is a higher seimaibuai worse sake?
Not necessarily. A higher number means a fuller, more rice-forward style, which many drinkers prefer, especially with food. It reflects a different intention, not lower quality.
Do all sakes list a seimaibuai?
Special-designation sakes must display it, and most do so prominently. Some inexpensive table sakes labelled simply as futsu-shu may not feature the number as clearly, but premium bottles almost always show it.
Written by Dr. Sake. For more label-decoding and the science behind the glass, follow us on Instagram @thesakeanatomy.
