The World of Traditional Japanese Fermented Seasonings

Hitomi
Sep 17
3 min read

Fermented food collage with soy sauce, herbs, bottles, and miso. Text reads "All About Fermented Seasonings" in the center.

Why Fermented Seasonings Matter More Than Ever

Fermented seasonings—those made using beneficial microbes like koji, lactic acid bacteria, and yeast—are not just culinary traditions. They’re biological powerhouses that influence:

How our food is digested: microbes and enzymes break down proteins and starches into simpler molecules, making digestion easier.
Our nutrient uptake: fermentation can increase bioavailability of vitamins and minerals, and sometimes create new beneficial compounds like bioactive peptides.
Gut microbiome diversity & immune signaling: live cultures from fermented foods (if unpasteurized) help seed diversity and stimulate immune health.

Five Traditional Japanese Fermented Seasonings (and Things to Watch For):

1. Soy Sauce (醤油 | Shoyu)

Close-up of a Kikkoman Smooth Aromatic Soy Sauce bottle, hand-held in a store aisle. Visible are nutrition facts and ingredients text. — **Nama Shoyu (生醤油, “raw soy sauce”)**

Made by fermenting steamed soybeans and roasted wheat with koji, then aging the mixture (moromi) with saltwater for several months. During this time, yeast and lactic acid bacteria develop the sauce’s complex flavor and aroma.
There are many varieties of soy sauce—dark (koikuchi), light (usukuchi), tamari, and more—each with its own regional style and use. One unique type is Nama Shoyu (生醤油, “raw soy sauce”), which is unpasteurized and never heat-treated. Because it isn’t heated, nama shoyu retains more of the live enzymes and microorganisms from fermentation, giving it a fresher, brighter flavor profile compared to regular soy sauce.

2. Miso (味噌 | Miso)

Supermarket shelf displaying various miso paste containers with colorful labels and prices, including $5.59 and $11.99, on a wavy patterned backdrop. — **Variety of Miso in Japanese Grocery Store**

Created by fermenting cooked soybeans with salt and koji (rice, barley, or soybean koji).
The result depends on the type of koji used: rice miso, barley miso, or soybean miso. Fermentation can last from one month to a year.
Watch for: Unpasteurized miso retains live enzymes and probiotics, offering more gut health benefits. However, it continues fermenting after packaging, so it requires careful storage. Most supermarket miso is pasteurized for stability, which reduces these live cultures.

3. Sake (酒 | Sake)

Green sake bottle with "Hakkaisan Junmai Daiginjo 45" label. Info includes ingredients, alcohol content, and a QR code. Background shows shelves. — **Good Example of Sake**

While often thought of as a beverage, sake also functions as a fermented seasoning in Japanese cooking.
Rice starches are converted into sugar by koji, then yeast ferments the sugars into alcohol. When used in cooking, sake softens flavors, balances seasoning, and reduces unwanted odors.
Watch for: Many “cooking sake” products contain added salt, sugar, or other ingredients. For purer flavor and control, use drinking-quality sake instead of cooking sake.

4. Rice Vinegar (米酢 | Kome-Su)

A large bottle of Mizkan rice vinegar with a yellow label featuring Japanese text. It's placed on a wooden surface with a paneled background. — **Pure “junmai-su” (純米酢), made only from rice**

Produced by fermenting sake (made from rice) with acetic acid bacteria. Pure rice vinegar has a mellow umami and gentle sweetness.
Watch for: Some commercial products add brewed alcohol (醸造アルコール) or other grains. For the best flavor and gut health benefits, look for pure “junmai-su” (純米酢), made only from rice.

5. Mirin (本みりん | Hon Mirin)

Bottles of Mirin displayed on a grocery store shelf, organized by type. Visible price tags, vibrant red caps, and colorful labels. — **Variety of Mirin in Japanese Grocery Store**

A naturally sweet seasoning created by fermenting steamed glutinous rice with rice koji and shochu (a distilled spirit). The enzymes in koji transform starches into sugars, giving mirin its characteristic sweetness and umami depth.
Watch for: Authentic “hon mirin” (本みりん) is fermented and contains natural sugars and alcohol. In contrast, “mirin-style” seasonings (みりん風調味料) are cheaper imitations made with sweeteners and lack the depth and health benefits of true fermented mirin.

Koji-Based Seasonings: Salt Koji, Soy Sauce Koji, and Sweet Koji (Amazake)

In addition to the classics above, newer Koji-based seasonings like Salt Koji, Soy Sauce Koji, and Sweet Koji (Amazake) have become popular in modern kitchens:

Salt Koji acts as a natural tenderizer and umami booster, transforming meats and vegetables with its enzymatic power.
Soy Sauce Koji blends the familiar flavor of soy sauce with live koji cultures, adding depth and a slight sweetness.
Amazake is a lightly sweet, drinkable seasoning made from rice koji, often used as a sugar alternative in desserts and drinks.

These versatile ingredients are not only flavorful but also bring probiotics and enzymes that support gut health.

Final Thoughts

Fermented seasonings are more than just condiments—they represent centuries of Japanese wisdom in preserving food, enhancing taste, and supporting wellness. From miso soups to pickles, marinades to sauces, they form the foundation of Japanese cuisine.

Whether you choose classic seasonings like soy sauce and miso or experiment with modern favorites like salt koji and amazake, these ingredients offer a simple way to add flavor and gut-friendly benefits to your cooking.

✨ Happy Fermenting!