Miso soup.

Soy sauce.

Natto.

Sake.

Pickles.

They might seem like completely different parts of Japanese food culture.

But many of them have something in common:

Fermentation.

For centuries, people in Japan have used fermentation to preserve ingredients and create entirely new flavors from simple foods like rice, soybeans and vegetables.

Today, fermented foods are everywhere in Japanese cuisine.

Some are mild and comforting.

Some are sweet.

Some are intensely savory.

And some are famously...

sticky, stringy and smelly.

Welcome to the fascinating world of Japanese fermented foods (発酵食品 / hakkō shokuhin).

What Are Japanese Fermented Foods?

Fermentation happens when microorganisms such as bacteria, yeast or molds transform ingredients over time.

Before refrigerators existed, fermentation was an important way to preserve food.

But preservation wasn't the only benefit.

Fermentation also creates flavor.

It can make foods sweeter, sourer, richer and especially more umami.

In Japan, fermentation became deeply connected to everyday cooking.

In fact, you may already eat Japanese fermented foods without realizing it.

Soy sauce?

Fermented.

Miso?

Fermented.

Natto?

Very fermented.

And one ingredient sits at the center of much of this tradition.

Koji (麹): The Heart of Japanese Fermentation

If you want to understand Japanese fermented food, start with koji (麹).

Koji is made by cultivating koji mold (Aspergillus oryzae) on grains such as steamed rice or barley.

Pronounced approximately:

koh-jee.

It doesn't look particularly dramatic.

But koji plays a role in making some of Japan's most important foods and drinks, including:

🍲 Miso
🥢 Soy sauce
🍶 Sake
🍚 Amazake
🧂 Shio koji
🍶 Mirin

Koji produces enzymes that help break down starches and proteins, creating sweetness and rich savory flavors.

Think of koji as one of the quiet engines behind Japanese cuisine.

You don't always see it.

But it's everywhere.

Natto (納豆)

Perhaps Japan's most famous fermented-food challenge.

Natto (納豆) is fermented soybeans known for their distinctive aroma and incredibly sticky, stringy texture.

It's commonly eaten over hot rice, often at breakfast.

Lift a bite with your chopsticks and you'll quickly discover what makes natto famous.

The strings just...

keep going.

Some people love natto.

Some people learn to love natto.

And some people decide they've been adventurous enough for one day.

 

Miso (味噌)

Miso is probably one of the most familiar Japanese fermented foods around the world.

Miso (味噌) is a fermented paste commonly made from soybeans, salt and koji.

There isn't just one type.

Different ingredients, regions and fermentation methods create miso ranging from mild and sweet to dark, salty and intensely savory.

You'll find it in much more than miso soup.

Miso appears in sauces, marinades, dressings, hot pots and countless home-cooked dishes.

 

Amazake (甘酒)

Despite having sake in its name, amazake isn't necessarily an alcoholic drink.

Amazake (甘酒) is a traditional sweet Japanese drink that can be made using rice and rice koji.

The enzymes from the koji transform the rice starches into sugars, creating natural sweetness.

The result is creamy, comforting and surprisingly sweet.

And despite looking like the perfect winter drink, amazake also has a long connection with summer in Japan.

 

Nukazuke (ぬか漬け)

Japanese fermentation isn't only about soybeans and koji.

It can also involve...

rice bran.

Nukazuke (ぬか漬け) are vegetables fermented in a seasoned rice-bran bed called nukadoko (ぬか床).

Cucumbers, eggplant, daikon and carrots are common choices.

Traditional nukadoko requires regular care and mixing.

Which means some households essentially have...

a fermentation pet living in the kitchen.

Except this one gives you pickles.

 

Soy Sauce (醤油)

Yes.

That bottle sitting beside your sushi is fermented too.

Japanese soy sauce (醤油 / shōyu) is traditionally produced using ingredients including soybeans, wheat, salt and koji.

Fermentation and aging transform those simple ingredients into the dark, deeply savory seasoning found throughout Japanese cuisine.

It's so ordinary that it's easy to forget how extraordinary the process behind it actually is.

 

Sake (日本酒)

Japan's famous rice drink also belongs in the fermentation story.

Making sake (日本酒 / nihonshu) depends on the relationship between rice, koji and yeast.

Koji helps transform starch in the rice into sugars, while yeast helps turn those sugars into alcohol.

So the same fermentation culture behind miso and soy sauce also helps create one of Japan's most famous drinks.

Not a bad résumé for some mold growing on rice.

Why Does Japan Have So Many Fermented Foods?

Fermentation developed for practical reasons.

It helped preserve food before modern refrigeration.

But over generations, preservation techniques also became part of regional food traditions and everyday cooking.

Japan's climate, agricultural traditions and staple ingredients such as rice and soybeans created an especially rich environment for fermented foods.

And fermentation gave Japanese cooking something incredibly important:

flavor.

Especially umami.

That's why fermentation isn't some unusual corner of Japanese cuisine.

It's part of the foundation.

Japanese Fermented Foods at a Glance

Japanese fermentation comes in many forms—from sticky soybeans to sweet rice drinks.

Here’s a quick guide to some of the fermented foods you’ll encounter in Japan:

Food	Japanese	What Is It?	What to Expect
Koji	麹	Rice or grains cultivated with koji mold	Sweet, fragrant and the foundation of many Japanese fermented foods
Natto	納豆	Fermented soybeans	Sticky, stringy and famously distinctive
Miso	味噌	Fermented soybean paste	Rich, salty and full of umami
Shio Koji	塩麹	Koji fermented with salt and water	Salty, slightly sweet and deeply savory
Amazake	甘酒	Traditional sweet fermented rice drink	Creamy, gentle and naturally sweet
Nukazuke	ぬか漬け	Vegetables fermented in rice bran	Crunchy, salty and slightly sour
Soy Sauce	醤油	Fermented soybean and wheat seasoning	Deep, savory and packed with umami
Sake	日本酒	Fermented rice drink	From light and delicate to rich and complex

You probably already eat more Japanese fermented foods than you realized.

And each one has its own story. 🇯🇵

Where Should a Beginner Start?

You don't have to begin your Japanese fermentation adventure with natto.

In fact...

maybe don't. 😆

Start with something familiar.

Miso is an easy introduction.

Then explore shio koji, amazake or nukazuke.

And eventually...

when you're feeling brave...

open the natto.

Mix it.

Lift your chopsticks.

Watch those strings stretch across the table.

You may discover your new favorite food.

Or you may discover that miso was perfectly fine.

Either way:

welcome to Japanese fermentation. 🇯🇵

Frequently Asked Questions

What are Japanese fermented foods?

Japanese fermented foods are foods and seasonings produced with the help of microorganisms such as bacteria, yeast and molds. Examples include miso, natto, soy sauce, sake, amazake and nukazuke.

What is koji?

Koji (麹) is made by cultivating koji mold on grains such as rice or barley. It's an important ingredient in traditional Japanese foods and drinks including miso, soy sauce, sake and amazake.

Is natto fermented?

Yes. Natto is made from fermented soybeans and is famous for its sticky, stringy texture and distinctive aroma.

Is miso fermented?

Yes. Miso is a fermented paste commonly made using soybeans, salt and koji.

Is soy sauce fermented?

Yes. Traditional Japanese soy sauce is produced through fermentation and aging.

Are all Japanese pickles fermented?

No. Tsukemono (漬物) is a broad category of Japanese pickles, and different types are prepared in different ways. Nukazuke are one well-known fermented variety.

Which Japanese fermented food should beginners try?

Miso is probably the easiest place to start because its savory flavor is already familiar to many people. After that, try shio koji, amazake or Japanese fermented pickles before tackling natto.

🇯🇵 Keep Discovering Japan

If you enjoyed discovering Japanese fermented foods, you might also like learning about amazake (甘酒), Japan’s traditional sweet rice drink made with koji.

👋 Meet a JapPop Resident

Soy Mate

しょうゆさし君

A loyal little soy companion who's happiest swimming beside a plate of sushi. 🍣

Soy Mate takes his job very seriously.

Wherever sushi goes, he follows.

Filled with one of Japan's most familiar fermented seasonings, he's proof that fermentation might already be sitting on your table.

👉 Meet Soy Mate and discover more residents from the JapPop Universe.

🇯🇵 About JapPop

At JapPop, we celebrate Japanese culture through playful illustrations, original characters, and stories inspired by everyday life in Japan.

From beloved foods and traditional festivals to folklore, historical figures, seasonal customs, lucky gods, and language, every article introduces another piece of Japan—and another story worth discovering.

Sometimes Japanese culture is hidden in an ancient tradition.

Sometimes it's sitting quietly in your bowl of miso soup.

And sometimes...

it's stretching from your chopsticks in one very long natto string. 🫘

Discover Japan, one story at a time. 🇯🇵✨