Rice Has No Sugar — So How Does Sake Become One of the World’s Strongest Brewed Drinks?

Our map left one riddle unanswered: sake is a brewed drink, never distilled, yet undiluted it reaches nearly 20% alcohol. Beer tops out around 5–9%, even wine around 14–15% — so why can sake alone climb so high?

The answer lies in one of the most labor-intensive fermentation methods in the world, hidden inside how sake is made. It is called parallel multiple fermentation (heikō-fukuhakkō). It sounds technical, but one comparison makes it click.

First, alcohol is born from sugar

Every alcohol begins at the same point: yeast eats sugar and turns it into alcohol. That is fermentation. No sugar, no alcohol.

Here wine has it easy. Grape juice is already full of sugar. So making wine is a single job — add yeast, let it ferment.

But rice has no sugar. It has starch, and yeast cannot eat starch. Someone must first turn that starch into sugar.

Beer does it “in sequence,” sake does it “at the same time”

Beer, made from barley, faces the same problem — barley has starch, not sugar. Beer solves it like this: first convert the starch into sugar, and only when that is finished, add the yeast to ferment. Two jobs, done one after the other.

Sake takes one step beyond the world’s norm. It houses a partner called koji in the rice and runs both jobs — turning starch into sugar, and fermenting that sugar — inside the same tank, at the same time. That is parallel multiple fermentation.

Wine is “one job,” beer is “two jobs in sequence,” sake is “two jobs at once.” The wisdom of brewing grows one step more intricate along that line.

Why “at the same time” makes a stronger drink

The secret is how long the yeast can be kept working.

As fermentation proceeds, the yeast grows less and less able to withstand the alcohol it has itself produced. Wine yeast hits this “alcohol wall” relatively early, and the strength gives out around 14–15%.

Sake raises that wall in two ways. One is parallel fermentation: koji makes sugar little by little and the yeast eats it right away, so the sugar in the tank stays thin throughout and the strain on the yeast stays light. The other is that the yeast used for sake has itself been selected, over long years, for strains that are strong against alcohol. Together, these two let sake reach — without any help from distillation — a strength that stands among the highest of the world’s brewed drinks (close to 20% undiluted). That is the answer to the riddle we opened with.

Most sake is sold at 15–16% because water is added afterward to adjust the strength. Sake with no water added — genshu — reaches a robust strength of around 18%.

The partner, koji — the “national fungus” behind the Japanese kitchen

The star of this feat is koji: steamed rice cultured with a beneficial microorganism called koji-kin. This same microorganism gives rise to miso, soy sauce, and mirin — a foundation of Japanese food culture, and one officially designated Japan’s “national fungus.”

In other words, sake is not some far-off foreign technology. It is born from the very same fermentation wisdom as the miso and soy sauce used in the kitchen every day.

Common misconceptions:

• “Sake is rice wine.” → In craft it is closer to beer (it has a starch-to-sugar step). As the map said: brewed like a beer, savored like a wine.
• “Sake is distilled.” → It is not. Its strength comes from parallel fermentation, not distillation.
• “High strength means it belongs with shochu or vodka.” → At around 15%, sake sits between wine and beer by strength alone — a completely different family from strong distilled spirits.

All you need to remember

1. Rice has no sugar — so it needs a partner, koji, to turn starch into sugar.
2. Saccharification and fermentation run at the same time — that is parallel fermentation. Beer does it in sequence; sake does it at once.
3. That is how it reaches, without distillation, a strength among the world’s highest brewed drinks — and that koji comes from the same kitchen wisdom as miso and soy sauce.

Grasp these three, and you can already describe “what sake is” more accurately than many people in Japan.

— But then, why is that rice “polished” before brewing? What does the “polishing ratio” on the label actually grind away? And why does one and the same sake change its expression with temperature? From here, we step into the story of flavor.

Read next: What Is Shochu? (available now) / The Map of Japanese Alcohol (available now) / Pairing Basics (available now) / Glossary of Japanese Drinks (available now)