Introduction
Fermentation has always been about transformation. With the help of microbes, humans learned to turn milk into cheese, grains into beer, and cabbage into kimchi. It preserved food, created nutrition, and unlocked flavors that raw ingredients could never carry on their own.
At Fermenthings, we take this ancient tool and give it a new role. We call it circular fermentation: using fermentation to close loops, to prevent waste, and to make sure that every ingredient gets a second, third, or even fourth life. In other words: why waste it, when you can taste it.
This is part of the RotFest presentation given on September 29 2025
A Short History of Circular Thinking
If you look at food traditions, the idea isn’t new.
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Brewers gave their spent grain to bakers and farmers.
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Korean kitchens fermented every leaf and root into kimchi.
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Vinegars were born from wines that had “gone bad.”
What we do today is simply make this logic visible again. Circular fermentation is about treating “waste” as the starting point for the next taste.
How It Works (Science Made Simple)
Microbes are our partners.
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Lactic acid bacteria turn sugars into lactic acid → the backbone of pickles and kimchi.
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Acetic acid bacteria convert alcohol into vinegar → wines, beers, teas become bright and sharp.
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Koji molds unlock enzymes that break down starches and proteins → creating miso, shoyu, and garums.
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Yeasts ferment sugars into alcohol and CO₂ → bread, beer, kombucha.
When you combine these pathways with side-streams, you don’t just reduce waste — you open doors to whole new taste worlds.
Four Paths of Circular Fermentation
Vinegars
What seems like an “end” can actually keep evolving. Flat beers, overripe fruits, or herbal stems become the foundation for complex vinegars.
Example: Shiso Vinegar made with surplus shiso leaves from Courjette CSA — preserving seasonal freshness long after harvest.
Powders
What’s left behind after pressing shoyu or garum? Dense fibers full of umami. Dry them, blend them, and you have a seasoning powder, perfect for caramelizing onions, enriching stocks, or sprinkling into sauces. It’s a spice born directly from fermentation’s leftovers.
Koji Family (Miso, Shoyu, Garum)
Koji is the engine of transformation. With it, bread crusts, beer grains, or even nori can become deeply savory sauces.
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Nori Garum with seaweed from a Cantillon Zwanze experiment.
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Beer Sludge Shoyu using yeast from La Source brewery, inspired by La Païssée in Switzerland.
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Fruitpap Garum turning jam residues into fruity umami.
Each sauce is proof that nothing is fixed: waste becomes seasoning, side-streams become signature flavors.
Lactofermentation
This is where vegetables find new lives. At Fermenthings, we don’t just use the “perfect” cabbage — we ferment carrot tops, outer leaves, radish greens, and seasonal odd bits. Together, they create kimchi scraps that are collective, surprising, and never the same twice.
As we wrote in our Ferment Lab notes: it’s about honoring every leaf, root, and stem, and letting the microbes weave them into something greater than the sum of its scraps.
Current Experiments on the Shelves
Circular fermentation is not an idea in a book; it’s jars, bottles, and powders on our shelves. Right now, members can take home six experiments fresh from the Ferment Lab:
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Nori Garum with nori from @brasseriecantillonofficiel’s Zwanze experiment.
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Beer Sludge Shoyu with yeast from @la_source_beer_co, inspired by @lapaisee.
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Shiso Vinegar from @courjette_csa harvest.
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Fruitpap Garum from jam leftovers.
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Hot Sauce blending this year’s full pepper harvest.
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Strawberry Habanero Jam for those who like sweet heat.
Each product is a story of collaboration, surplus, and microbial creativity.
Why It Matters
Circular fermentation is bigger than flavor. It’s a way to think differently about food systems:
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No linear chains, only loops.
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No “waste,” only starting points.
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No separation between tradition and innovation — microbes make both possible.
It’s also a metaphor. Just as bacteria, molds, and yeasts collaborate to transform food, humans can collaborate to transform the way we eat, produce, and share resources.
Motto
Why waste it, when you can taste it.