Sake · Production · Study guide
How Sake Is Made
A study guide to how sake is brewed — the four ingredients, multiple parallel fermentation, and the six steps from polished rice to the finished bottle.
Sake is often shelved beside wine and called "rice wine", which is the first thing to unlearn. Wine ferments in a single step — the grape already carries its own sugar, and yeast simply turns it into alcohol. Rice carries no sugar, only starch, so sake has to solve a problem wine never faces: something must convert the starch to sugar before the yeast can work. That job belongs to a mould called kōji, and the way sake does it — starch-to-sugar and sugar-to-alcohol happening at the same time, in the same tank — is the single idea the whole drink hangs on.
Get three things straight — sake is brewed (closer to beer than to wine), it runs on just four ingredients, and its fermentation is a two-conversions-at-once trick called multiple parallel fermentation — and the rest of the process falls into an orderly line. This guide is the map; each step below has its own guide that goes deeper.
The one thing to fix first: sake is brewed, and two conversions run at once
Only four things go into ordinary premium sake:
- Rice — the source of starch, and so of all the sugar and most of the flavour.
- Water — over three-quarters of the finished drink, and a real influence on style.
- Kōji — steamed rice colonised by the mould Aspergillus oryzae, which secretes the enzymes that break starch into sugar.
- Yeast — which ferments that sugar into alcohol and throws off the aromas.
In beer, the two conversions are separate: you mash the grain to make sugar, then ferment it. In sake they are simultaneous — kōji is releasing sugar and yeast is eating it in the very same vessel, moment to moment. This is multiple parallel fermentation (heikō fukuhakkō), and because the sugar never piles up, sake can ferment to a naturally high strength — often 18–20% ABV before any water is added, higher than any other brewed drink.
The six steps, in order
This is the sequence worth knowing cold. Each links to its own guide.
| # | Step | What happens |
|---|---|---|
| 1 | Polishing (rice & polishing) | The brown rice is milled to remove its fatty, protein-rich outer layers, exposing the starchy heart |
| 2 | Washing, soaking, steaming | The polished rice is cleaned, brought to a precise moisture level, and steamed — firm outside, soft inside |
| 3 | Kōji making (kōji) | Kōji mould is cultivated on part of the steamed rice over ~48 hours to build the starch-splitting enzymes |
| 4 | The starter — shubo/moto (fermentation) | A small, dense seed mash of rice, kōji, water and yeast, protected by lactic acid |
| 5 | The main mash — moromi | Rice, kōji and water are added in three stages over four days; parallel fermentation runs ~2–5 weeks |
| 6 | Pressing & finishing (pressing & finishing) | The mash is pressed off its lees, then (usually) filtered, pasteurised, matured and diluted to bottling strength |
Key facts
| What it is | A brewed alcoholic drink made from rice, water, kōji and yeast |
| Fermentation | Multiple parallel fermentation — starch→sugar and sugar→alcohol at once |
| Starch converter | Kōji mould (Aspergillus oryzae) and its amylase enzymes |
| Strength | ~18–20% ABV in the tank; usually diluted to ~14–16% for bottling |
| Two categories | Futsū-shu (ordinary) and premium (grades of sake) |
| Timeline | Roughly 60–90 days start to finish; the main fermentation ~2–4 weeks |
Multiple parallel fermentation, briefly
Picture one tank. Grains of kōji, riddled with enzymes, are steadily unlocking sugar from the steamed rice. Yeast cells, surrounding them, consume that sugar the instant it appears and turn it into alcohol and aroma. Neither gets ahead of the other: sugar is released only as fast as it is eaten, so it never accumulates to a level that would stall the yeast. That balance is why sake reaches such a high natural ABV, and why controlling temperature — which sets the pace of both conversions — is the brewer's main lever over style. Cool and slow builds the fragrant, fruity aromatics; warm and fast builds body and savour.
In this guide
The full guide below walks the whole journey and shows where style is actually decided:
- The six steps in more detail, from milling to bottling
- Where each style choice is made — and which step decides it
- How sake differs from wine and beer, side by side
- Why the finished sake is diluted, and what genshu means
- Classic exam questions
The journey, step by step
1. Polishing (seimai). Brown rice is milled in tall vertical mills that grind away the outer grain. The seimai-buai — the percentage of the grain remaining — is the number that later separates the premium grades: 70% for honjōzō, 60% for ginjō, 50% or less for daiginjō. The more you polish, the cleaner and more fragrant the sake, and the more rice (and cost) you throw away. See rice & polishing.
2. Washing, soaking, steaming. The polished grains are washed and then soaked to an exact water content — for the most polished rice, timed to the second. Steaming (not boiling) firms the outside of each grain while leaving the inside soft, the texture kōji mould and yeast both need.
3. Kōji (seigiku). About a fifth to a third of the steamed rice is carried to a warm, humid kōji room, dusted with spores of Aspergillus oryzae, and tended over roughly two days until each grain is threaded with enzyme-rich mould. Kōji is the engine of the whole process — no kōji, no sugar, no sake. See kōji.
4. The starter (shubo or moto). Brewers first build a small, concentrated mash — rice, kōji, water and yeast — to grow a strong, healthy yeast population. Because it must stay clean, it is protected by lactic acid, either added directly (the fast, modern sokujō method) or generated by wild bacteria over weeks (the traditional kimoto and yamahai). See fermentation.
5. The main mash (moromi). The starter is scaled up into the main fermentation by adding rice, kōji and water in three stages over four days (sandan shikomi), so the yeast is never overwhelmed. Parallel fermentation then runs for about two to four weeks — cool and long for delicate ginjō, warmer and shorter for rich junmai.
6. Pressing & finishing. Once fermentation is complete the mash is pressed to separate the clear sake from the white lees (sake kasu). Most sake is then filtered, pasteurised for stability, rested to mature, and diluted with water down to drinking strength. Each of these is a style choice — leave one out and you get a named style (unpasteurised nama, undiluted genshu, unfiltered muroka). See pressing & finishing.
Sake, wine and beer, side by side
| Sake | Wine | Beer | |
|---|---|---|---|
| Base | Rice (starch) | Grapes (sugar) | Malted grain (starch) |
| Making sugar | Kōji mould enzymes | Already in the fruit | Malting + mashing |
| Fermentation | Starch→sugar & sugar→alcohol at once | Single step | Two separate steps |
| Typical strength | ~15–20% | ~11–15% | ~4–6% |
The headline is that sake is brewed, like beer, but performs beer's two jobs simultaneously rather than in sequence — and that is exactly why it ferments so strong.
Why sake is diluted
Fresh from the press, sake sits around 18–20% ABV — too strong and unbalanced for most drinking. Brewers add pure water to bring it down to roughly 15%, tuning the balance as they go. Sake bottled without this step is labelled genshu (undiluted), and drinks noticeably fuller and hotter. The water used for dilution matters as much as the brewing water, which is why a brewery's location — soft-water Fushimi, hard-water Nada — leaves its fingerprint on the style (regions of Japan).
Classic exam questions
- What are the four ingredients in premium sake? — rice, water, kōji, and yeast.
- What is kōji, and what does it do? — steamed rice grown with Aspergillus oryzae mould; its enzymes convert rice starch into fermentable sugar.
- What makes sake's fermentation unusual? — multiple parallel fermentation: starch is converted to sugar and sugar to alcohol at the same time, in the same tank.
- Roughly what strength does sake reach before dilution? — about 18–20% ABV.
- Name the three-stage addition of the main mash. — sandan shikomi.
- What is undiluted sake called? — genshu.
Fix the four ingredients and the two-conversions-at-once idea, and every later choice — how far to polish, which starter, how warm to ferment, whether to filter or pasteurise — reads as a knob on the same simple machine.