It sounds like a laboratory or grandmother's sauerkraut barrel, but in both cases, it relies on the exact same principle, just in different dosages.
At Bonvivant, it is one of our most essential tools for bringing depth to our dishes. In this article, we explain what fermentation actually is, what Koji, Miso, and Umami are all about, and how you can get started yourself without setting up a full laboratory.
What fermentation actually is
During fermentation, microorganisms such as bacteria, yeasts, or molds transform ingredients into something entirely new. They break down sugars, starches, or proteins, producing acids, alcohol, aromas, and new textures along the way.We know this principle from everyday life without even thinking about it: bread, beer, wine, vinegar, yogurt, and sauerkraut are all fermented foods. Depending on the microorganism involved, completely different results emerge.
| Type of Fermentation | Organism at Work | Typical Examples |
|---|---|---|
| Lactic acid fermentation | Lactic acid bacteria | Sauerkraut, kimchi, fermented vegetables |
| Yeast fermentation | Yeasts | Bread, beer, wine |
| Acetic acid fermentation | Acetic acid bacteria | Vinegar |
| Koji fermentation | Mold fungus Aspergillus oryzae | Miso, soy sauce, sake |
We have already described lactic acid fermentation in our seasonal calendar. Here, we want to focus on the supreme discipline that has been at home in Japanese cuisine for centuries: Koji.
Koji: The mold that turns rice into umami
Koji originally refers to rice inoculated with the mold fungus Aspergillus oryzae. In everyday Japanese usage, the word often stands for the fungus itself as well as related cultures such as Aspergillus sojae. The mold is added to steamed rice or soybeans, transforming them into a white, fluffy mass. It has been used for more than a thousand years to produce soy sauce, miso, and sake.What happens on a detailed level is fascinating. The fungus cannot absorb the nutrients in the grain directly, which is why it releases its own built-in tools, so-called enzymes, that break them down in advance. Koji produces more than 50 different types of these diligent helpers. Some break down starches into sugars, making Koji the foundation for sake. Others break down proteins into their smallest building blocks, the amino acids.
The most common building block created in this process is glutamic acid. And that is precisely the secret behind the flavor we call umami: that hearty, mouth-coating depth we otherwise know from rich broths, aged cheese, or sun-dried tomatoes. That is why Koji is so invaluable for plant-based cuisine: it magic-keys this savory depth straight out of plant ingredients, completely without animal products.
Miso, Shoyu, and Relatives
Some of the world's most famous seasonings originate from Koji.Miso, the Japanese paste, is crafted from soybeans, Koji, and salt, and is aged for varying lengths of time depending on the variety, from a few weeks to several years.
Shoyu, Japanese soy sauce, is made from soybeans and grain with Koji. Both deliver salt, sweetness, and above all, concentrated umami.
This principle is known outside Japan as well: the ancient Romans seasoned their food with garum, a fermented fish sauce. Today, many plant-based kitchens transfer this concept to Koji and botanical ingredients, creating equally deep seasoning sauces entirely without fish.
Shio Koji: The flavor turbo-booster for vegetables
Among Koji specialties, Shio Koji occupies a truly special place for us at Bonvivant. Behind it lies a mixture of Koji rice, water, and sea salt, allowed to mature at room temperature for one to two weeks. During this time, the Koji enzymes gradually break down the starches in the rice into gentle sweetness while simultaneously splitting proteins. The result is a thick, slightly sweet seasoning sauce packed with natural umami power.For us, Shio Koji is the ultimate marinade wildcard. When we steep tender root vegetables, mushrooms, or fruits in it before cooking, the active Koji tools gently crack open the surface of the ingredients and unlock their flavor depth. When the vegetables subsequently hit the hot pan or grill, the released fruit sugars and protein blocks ensure beautiful caramelization and wonderfully intense roasted aromas in no time. The vegetables gain real bite and roasted notes while remaining delightfully juicy on the inside.
Shio Koji is for us therefore far more than just a pinch of salt: it is arguably the finest shortcut to incredible flavor.
Why fermentation is so essential for vegan cuisine
When cooking without meat, fish, and dairy, depth must be generated through other means. Fermentation is one of the most powerful tools for this because it does not merely add flavor, it transforms it. Nikodemus Berger puts it succinctly:„…not a poor preliminary stage to something else, it is the goal."Behind this lies an attitude we have represented right from the start: we do not want a cuisine that imitates animal products. Our head chef emphasizes that he was never interested in recreating animal ingredients, but rather wanted to develop independent innovations that impress with their own textures and presentations. When transitioning to vegan cuisine, we intentionally avoided convenience products and substitutes.
- Nikodemus Berger, Head Chef at Bonvivant, on a turnip fermented with Koji
Fermentation is therefore not a makeshift solution for us, but a craft.
Fermentation at Bonvivant
Nikodemus works with Japanese fermentation techniques, Nordic flavor profiles, and French precision. What that means in practice shows in the effort involved: a turnip fermented for weeks with Koji is not a side dish for us, it is the main event.Plant-based Michelin-star cuisine is labor-intensive, not because meat is missing, but because of the craftsmanship replacing it, such as weeks of fermentation, hours of reductions, Koji aging, and processing from root to leaf.
At the same time, fermentation is a sustainability tool for us. In our entry in the Guide Michelin, we describe how we reduce waste by fermenting. What is left over in the kitchen gets a second chance instead of ending up in the bin. This fits seamlessly with our root-to-leaf philosophy.
And we love sharing this knowledge: in October 2025, for example, we hosted a workshop dinner in our Studio32 together with Jamie Unshelm, head of the Culinary Lab at Rote Wand in Lech, under the title „Vorarlberg fermentiert", where alpine flavor profiles met an urban food lab. The menu included fermented sourdough bread with pickles and a black walnut tapenade.
Fermentation in the glass: Sake, sherry, and Kellerbier
Fermentation does not stop on the plate. Many drinks also owe their depth to microorganisms, and right here the circle closes with our bar. Sake is created because Koji transforms the starch in rice into sugar, which yeasts then turn into alcohol. Bread, beer, and wine thrive on yeast fermentation. In reviews of our beverage pairing, it has already been highlighted that sake, Kellerbier, and sherry are not missing from our cocktails. For us, this is a perfect match: those who work with fermentation in food will often find related flavors in the glass that embrace a dish rather than compete with it.
More than seasoning: Fermentation and texture
Fermentation alters not only flavor, but also texture. Vegetables become softer or crunchier depending on salt content and duration, pastes turn creamy, and liquids gain body. This makes ferments doubly valuable for plant-based cuisine, as texture, alongside taste, is typically the second area where meat and fish excel. Using fermented ingredients deliberately allows one to give a dish bite, creaminess, and depth without mimicking anything.
Good environment, good result: How to make a ferment succeed safely
Once you understand how fermentation works, there is no need to fear missteps. Essentially, it comes down to building a cozy home for the „good“ microorganisms while blocking the path for unwanted party crashers. The most important guardian in vegetable ferments is acidity. When lactic acid bacteria get to work, they rapidly produce enough acid so that harmful germs or molds stand no chance.Salt also plays a starring role here: when we preserve vegetables, salt draws excess water out of the plant cells. This creates the ideal brine where beneficial lactic acid bacteria feel right at home while unwanted bacteria are held at bay. When temperature and time line up, fermentation turns into a reliable, wonderful craft. It simply requires a touch of intuition and patience, rewarding you with fantastic flavors and complete safety.
Fermenting at home: How to get started
If you want to try it yourself, you don't have to start from scratch. Cultivating Koji from scratch is demanding, as temperature and hygiene must be spot on. For beginners, store-bought Koji rice, available in Asian markets and online, is ideal. You can use it to set up a simple seasoning sauce, letting it sit with salt and water for a few days at room temperature to marinate vegetables or tofu.A few rules apply to every fermentation: work with clean vessels and hands, keep ingredients submerged beneath the liquid, and give the process time. When fermenting vegetables, aim for a salt ratio of about two percent of the total weight, just as we described in our seasonal calendar. If the batch smells pleasantly sour, that is a good sign; if you spot colorful or foul-smelling mold, it is better to discard it. When in doubt, the rule remains: better safe than sorry.
What this means for your visit with us
When you dine with us, you often taste fermentation without seeing it: in the depth of a sauce, the acidity of a vegetable, or the lingering finish of a course. Anyone who wants to experience this firsthand can find all information about our current menu on our website.
FAQs - Frequently Asked Questions
What is Koji?Koji is rice or another grain inoculated with the mold fungus Aspergillus oryzae. It serves as the foundation for miso, soy sauce, and sake.
What does Koji have to do with Umami?
Koji splits proteins into amino acids, including glutamic acid, the substance behind the umami taste.
Is the mold on Koji dangerous?
The mold Aspergillus oryzae has been used for food for over a thousand years. For home experiments, the rule still applies: colorful or foul-smelling mold should be thrown away.
How do I start fermenting at home?
With simple setups like fermented vegetables or store-bought Koji rice. Clean vessels and sufficient salt are key.