What is kōso?

Japan spent a hundred years building a category of fermented plant extracts that almost nobody outside Asia can define, and the name it gave them, 酵素, points in slightly the wrong direction.

Enzymes will be the medicine of the future.

Dr. Hiromi Shinya · 新谷弘実

Japanese gastroenterologist, and a pioneer of modern colonoscopic surgery.

I · 酵素 · Kōso · enzyme

The word says enzyme. It undersells it.

In Japanese, 酵素 (kōso) literally means "enzyme." But what Japan came to call a kōso drink is much more interesting than an enzyme supplement, and that translation has caused decades of confusion outside the country.

Kōso refers to a category of slow-fermented botanical extracts, traditionally made by combining fruits, vegetables, herbs, roots, mushrooms, seaweeds and other plants, then allowing microorganisms and time to transform them. Some contain dozens of different plants, others more than one hundred. Some ferment for months; others mature for several years. And over the last century, these preparations have become deeply connected in Japan with fermentation culture, digestive rest, fasting and natural health.

But unlike miso, sake or natto, kōso isn't an ancient Japanese food. Its story is surprisingly recent.

A craftsman stirring a fermentation barrel beside a row of wooden-lidded vats

II · 歴史 · Rekishi · history

Kōso didn't always exist.

Japan has one of the richest fermentation cultures in the world. Miso, sake, soy sauce, vinegar, natto and countless regional fermented foods have been produced for centuries. Modern kōso drinks came much later, and their history can be traced to Hokkaido in the early twentieth century.

In 1926, Noboru Ohtaka (大髙登) began experimenting with botanical extracts after an experience using medicinal plants on an injury. His experiments gradually developed into something unusual: instead of extracting a single medicinal plant, he began working with large combinations of plant materials and allowing them to transform together.

1926

Ohtaka begins experimenting with botanical extracts in Hokkaido, after using medicinal plants on an injury.

1935

He establishes the Ohtaka Enzyme Research Association.

1950s

The work has developed into commercially produced multi-plant fermented extracts.

1957

One of Japan's earliest commercial kōso preparations enters the market.

III · 普及 · Fukyū · spread

From unusual tonic to Japanese wellness culture.

Kōso didn't become mainstream overnight. For decades it existed primarily within the worlds of Japanese natural health, fermentation and nutritional practice. As the category matured, Japanese makers built increasingly sophisticated recipes, combining wider families of fruits, vegetables, roots, mushrooms and seaweeds. Early formulations began with around 30 plants. Counts rose to 50, then 70, and some modern formulations now bring together more than 100 ingredients in a single ferment.

A close macro of tropical fruits — Fruits

A close macro of garden vegetables — Vegetables

A close macro of ginger, turmeric and galangal roots — Roots

A close macro of kombu seaweed — Seaweed

30plants
Early formulations
50plants
Recipes broadened
70plants
More botanical families
100+plants
Some modern formulations

Wild herbs with vegetables. Fruits with roots. Mushrooms with seaweed.

Different ingredients were chosen according to season and availability, then fermented or matured for months or years. Eventually 酵素ドリンク (kōso drinks) became a recognisable category within Japanese wellness culture.

And something else happened. People started fasting with them.

IV · 断食 · Danjiki · fasting

When Japan combined kōso with fasting.

Fasting itself was nothing new. Humans have fasted for religious, philosophical and health reasons for thousands of years, and Japan also had its own fasting traditions long before modern kōso existed. But during the twentieth century, a particularly Japanese approach began developing around fermented botanical extracts.

酵素ファスティング

Kōso fasting: "enzyme fasting."

Instead of consuming only water, people temporarily stopped eating normal solid meals while consuming measured amounts of fermented botanical extract diluted in water. It created a space somewhere between normal eating and complete fasting. Over time, an entire methodology developed around the practice.

準備期 · Preparation
For one or several days before fasting, food is progressively simplified. Alcohol, fried foods, highly processed foods, excessive sweets and heavy meals are generally reduced or removed. The idea is to transition gradually, rather than moving abruptly from normal eating into fasting.
ファスティング期 · Fasting
Solid food is temporarily removed or dramatically reduced. A fermented botanical extract is diluted with water and consumed periodically throughout the day, with water and other permitted fluids alongside it. Depending on the method, this might last one, three, five or occasionally more days.
復食期 · Refeeding
Then comes a stage often overlooked in Western fasting culture: returning to food. Normal eating doesn't necessarily resume immediately. Simple foods are introduced progressively and portions gradually increased. In many Japanese protocols, refeeding is considered part of the fast itself.

Preparation. Fasting. Recovery. The complete cycle matters.

2 days · preparation
3 days · fasting
2 days · recovery

During the fasting stage, a fermented preparation made from more than one hundred Japanese botanical ingredients is used alongside a structured protocol.

Other Japanese medical and nutritional organisations have developed their own approaches. The Clinical Molecular Nutrition Society has conducted supervised group fasting programmes since 2018, using preparation periods, fermented fasting drinks, fasting days and carefully controlled recovery periods. Professional organisations and certification programmes dedicated specifically to kōso fasting have also appeared.

What began as a botanical preparation gradually became part of a much larger Japanese culture around fermentation, nutritional rest and fasting.

VII · 実体 · Jittai · substance

But what actually is kōso?

This is where the language can become confusing. Despite the name, a kōso drink shouldn't simply be understood as a bottle containing digestive enzymes. Modern Japanese researchers increasingly use a more precise description.

植物発酵エキス · Plant Fermented Extract

The microorganisms involved in fermentation produce enzymes that interact with the original plant material. And those enzymes do something important: they transform it. Large molecules may be broken into smaller ones. Sugars are transformed. Organic acids accumulate. Plant compounds can be converted into different forms. Microbial metabolites appear.

The finished preparation is therefore no longer chemically identical to the fruits, vegetables, mushrooms and herbs that originally entered the fermentation vessel. It has become a fermented biological matrix derived from them.

This distinction matters. The older explanation of kōso was often "drink enzymes to replenish your body's enzymes." Today, we can describe the process much more accurately.

Plants + microorganisms + time = transformation.

VIII · 変化 · Henka · transformation

Fermentation is doing something to the plant.

This is perhaps the most fascinating part of the entire process. Fermentation doesn't simply preserve a plant. It changes it.

Microorganisms interact with plant material through enormous numbers of biochemical reactions. They consume certain compounds and release others. Their enzymes break chemical bonds. Some complex compounds become smaller metabolites. Glycosides can be transformed. The relative concentrations of phytochemicals can change. And entirely new microbial metabolites can appear.

You begin with one chemical environment. After a long fermentation, you have another.

IX · 原料 · Genryō · raw material

Why the quality of the plants matters.

And that brings us to one of the most overlooked aspects of kōso. You cannot separate the fermentation from what you ferment. If dozens of plants are going to be concentrated and fermented for months or years, the quality of those plants becomes fundamental.

This is why some of the highest-quality Japanese producers place enormous emphasis on their raw materials.

Seasonality.
Freshness at harvest.
Whole fruits and vegetables.
Peels.
Seeds.
Outdoor cultivation.
Soil quality.
And increasingly: organic agriculture.

Some contemporary Japanese kōso manufacturers work with ingredients carrying Japan's Organic JAS certification, the country's official organic standard. Certain producers ferment dozens of certified-organic fruits and vegetables, processing the plants without adding water and allowing the resulting extracts to ferment and mature for years. Others deliberately select seasonal, open-field-grown produce rather than relying entirely on greenhouse cultivation.

This attention to agriculture isn't incidental. The plants become the substrate for the entire fermentation.

Whole leaves, flowers and plant stems selected for fermentation

01

How was it grown?

02

What was sprayed on it?

03

What soil did it grow in?

04

When was it harvested?

05

Was the whole plant used?

06

Was it heated?

07

Was water added?

08

How long was it actually fermented?

09

How long was it matured?

Months

Shortest

One year

Common

Two years

Long

Sometimes three

Longest

XII · 東亜 · Tōa · East Asia

Beyond Japan: when fermentation met Asian herbalism.

The modern kōso category developed most clearly in Japan. But the idea didn't remain confined there. Across East Asia, it encountered cultures that already possessed something remarkably compatible with it: centuries of herbalism and fermentation knowledge.

Taiwan, South Korea and China subsequently developed their own modern cultures around fermented botanical extracts, sometimes combining fruits and vegetables with medicinal herbs, mushrooms, roots and traditional botanical ingredients. These aren't all the same tradition, and they shouldn't all simply be called Japanese kōso. But they increasingly share an important principle.

Don't just extract the plant. Ferment it.

A contemporary Kiwami kōso preparation rooted in East Asian fermentation culture

Taiwan · 酵素 · Jiàosù

Taiwan 酵素 (Jiàosù)

Taiwan became particularly important in the modern Asian fermented botanical industry. Interestingly, the Chinese term commonly used is 酵素 (jiàosù): the same Chinese characters used for kōso in Japanese, but pronounced differently.

Taiwan occupies an unusual cultural position. It has deep roots in Chinese herbalism, a history of Japanese influence and a sophisticated modern food and biotechnology industry. That created fertile ground for complex fermented preparations containing combinations of fruits, vegetables, herbs, mushrooms and other botanical ingredients.

Traditional herbs could become part of the fermentation substrate. Instead of simply extracting a plant into hot water, microorganisms could be allowed to interact with it over months or years. It created an interesting bridge.

Herbalism × Fermentation

Fresh garden vegetables prepared as botanical fermentation material

Korea · 효소 · Hyoso

Korea 효소 (Hyoso)

In Korean, enzyme is 효소 (hyoso). The broader modern category can also be described as 발효식물추출물, fermented plant extract.

South Korea already possessed one of the world's richest fermentation cultures.

Kimchi. Doenjang. Gochujang. Traditional vinegars. Fermented seafoods. Countless regional preparations.

This meant that the concept of using microorganisms to transform food was anything but foreign. Modern Korean researchers and manufacturers began applying fermentation techniques to medicinal plants traditionally used within Korean herbal medicine, 한의학 (Hanuihak). Ginseng is one of the best-known examples.

Rather than viewing fermentation simply as preservation, researchers became interested in its ability to biotransform herbal compounds. Fermentation can alter the chemical profile of a medicinal plant: certain compounds may become more or less abundant, others can be converted into smaller metabolites, and the microorganisms themselves can contribute additional metabolic products.

The question therefore changed.

"What does this plant contain?" → "What can this plant become?"

Reishi mushrooms among the botanical materials used in fermented preparations

China · 酵素 · Jiàosù

China 酵素 (Jiàosù)

China adds another dimension. The Chinese word 酵素 (jiàosù) is also widely encountered in the modern fermented botanical category, although the scientific term for enzyme in mainland Chinese is more commonly 酶 (méi).

Traditional Chinese herbal medicine has spent thousands of years exploring combinations of botanical materials. Rather than always searching for one active ingredient, classical formulas frequently combine multiple plants and prepare them through carefully defined processes.

Fermentation itself also has a historical place within Chinese materia medica: certain medicinal preparations have traditionally undergone microbial processing before consumption. Modern Chinese researchers have taken this principle further by investigating the controlled microbial fermentation of medicinal herbs and traditional herbal formulations. This creates a fascinating meeting point.

Ancient herbal formulation × Modern microbial fermentation

Traditional herbalism asked: which plants should we combine? Modern fermentation adds another question: what happens when microorganisms transform that combination before we consume it?

Regional names:
	NameWritten	PronunciationSpoken
Japan	酵素	Kōso
Taiwan	酵素	Jiàosù
Korea	효소 · 발효식물추출물	Hyoso · fermented plant extract
China	酵素 · 酶	Jiàosù · méi (enzyme)

Plants are not necessarily the final product. Sometimes they are the starting material.

植物 · Plant
Dozens of fruits, vegetables, roots, herbs, mushrooms and seaweeds.
微生物 · Microorganism
Enzymes break chemical bonds. Some compounds consumed, others released.
発酵 · Fermentation
Glycosides transform. Phytochemical ratios shift. New metabolites appear.
時間 · Time
Months, one year, two, sometimes three.
変化 · Transformation
One chemical environment in. Another out.

Nearly a century after the emergence of modern kōso culture in Japan, science gives us better language to understand what these traditions were exploring. We don't need to believe that drinking a fermented botanical extract simply "replaces" the enzymes inside the human body. The more interesting story is happening before we ever drink it: dozens of plants, thousands of biochemical interactions, a living fermentation process, and time.

That is kōso.

Sources and scope

A note on sources and scope.

A note on sources and scope. Dates, names and organisations follow the historical account of the category: Noboru Ohtaka's work from 1926, the Ohtaka Enzyme Research Association in 1935, commercial preparations from 1957, and the Clinical Molecular Nutrition Society's supervised programmes from 2018. The clinic protocol described is one example among several in use. Nothing on this page is a health claim, and nothing here is medical advice. Fasting protocols in particular are described as they are practised in Japan, not recommended.