What Solid-State Fermentation Tells Us About Mushroom Science
Fermentation has been part of human life for thousands of years. Today, fungi are used in fermentation to produce everything from foods and organic acids to enzymes and other compounds used across a wide range of industries. This process is called Fungal Solid-State Fermentation (FSSF).
But FSSF can also teach us something important about mushroom science: when mycelium grows, it doesn’t simply sit on top of its food source (or substrate). Instead, the mycelium transforms it into something entirely new.
What Is Fungal Solid-State Fermentation?
You may think that something like fungal solid-state fermentation would rarely affect your daily life, but it’s actually more common than you might think. For decades, FSSF has been a key process used in everything from industrial manufacturing to food production and preservation.
Humans have been using fungi to transform ordinary things into other useful or beneficial things through fermentation for a long time. In fact, humans have used FSSF to our benefit for far longer than we’ve had written records—dating back centuries to millennia in cultures around the world.*
Citric acid, for example, is a safe chemical compound that is produced almost exclusively through fermentation using fungi. Additionally, alternative leathers, bio-degradable packaging, agricultural products, and more are produced by fungal solid-state fermentation. You might also be surprised to learn that FSSF has even been essential to the production of antibiotics!
Fungal Solid-State Fermentation:
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Uses fungi to transform solid materials through fermentation
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Has been used by humans for centuries to millennia
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Supports food production, preservation, and ecology
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Is used to produce compounds such as citric acid, enzymes, and antibiotics
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Turns starting materials into chemically different finished materials
So, How Does FSSF Work in Practice?
First, you inoculate a sterilized solid substrate—like the organic brown rice used to grow Host Defense® Mushrooms™ functional mushroom supplements—with your desired fungus. Next, you grow the mycelium under carefully controlled conditions to optimize colonization, fermentation, and the production of bioactive compounds. In this way, FSSF provides a method to safely cultivate mycelium at scale while maintaining pure, uncontaminated growing conditions.*
When mushroom mycelium grows on brown rice through solid-state fermentation, the fungus gradually colonizes its food source and metabolizes the nutrients within it. Over time, compounds originally present in the brown rice significantly decrease, while other compounds increase or emerge through fungal growth and biotransformation.
In other words, the brown rice is being biologically transformed through fermentation by the mycelium.
The Process of Fungal Solid-State Fermentation:
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Begins with a sterilized solid substrate inoculated with a selected fungus
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Mycelium grows across and into the substrate as it colonizes it
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Fungal enzymes break down and metabolize nutrients in the food source
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Compounds in the original substrate decrease, change, or are transformed
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New fungal metabolites, lipids, enzymes, and other compounds are produced
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The result is a biologically and chemically transformed fermented material
Microscopic analysis helps make this fermentation process visible. As the mycelium colonizes brown rice, fungal hyphae permeate the original food source, demonstrating how the fungus utilizes the substrate as it grows. Fermentation transforms the chemical profile of the starting material as the fungus produces its own enzymes, metabolites, lipids, and other naturally occurring constituents.
This physical transformation is accompanied by significant chemical changes.
What Does Fungal Solid-State Fermentation Tell Us About Mushroom Science?
This is where solid-state fermentation challenges an overly simple way of thinking about mushroom ingredients.
Mycelium doesn’t absorb nutrients like plant roots. It digests and ferments food, breathes oxygen, and directly responds to its environment. When it has the right food and growing conditions, mycelium can produce hundreds—sometimes thousands—of naturally occurring beneficial compounds.*
It can be tempting to imagine cultivated mycelium and its substrate as two separate things: fungus on one side and grain on the other. But biology is more complicated—and more interesting—than that.
During fermentation, the mycelium actively interacts with its food source. It secretes enzymes, breaks down nutrients, incorporates materials into fungal tissue, and generates new metabolites. The original substrate is progressively transformed as part of that process. Compounds present in unfermented brown rice substantially decline, while other compounds associated with fungal metabolism and biotransformation through fermentation dramatically increase.
That means the finished fermented material is chemically different from the raw ingredients that it started with.
And that may be one of the most important lessons solid-state fermentation offers mushroom science: to understand a mushroom ingredient, we need to study the biological process that creates it—not simply measure what was present at the beginning.
The more closely we examine that process, the clearer it becomes that mycelium, fermentation, substrate, and time all contribute to the chemistry of the finished material.
Fungal Solid-State Fermentation Tells Us That:
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Mycelium digests and ferments its food rather than absorbing nutrients like plant roots
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Mycelium completely breaks down the substrate as it ferments
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Fungal growth can potentially produce thousands of naturally occurring compounds
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The chemistry of the material changes throughout the fermentation process
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The finished ingredient cannot be fully understood by looking only at its starting materials
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Mycelium, substrate, growing conditions, and time all influence the finished chemical profile
What Does Solid-State Fermentation Mean for Functional Mushroom Supplements?
The way a mushroom ingredient is grown matters. Mushroom mycelium requires a food source to grow, and with solid-state fermentation, that relationship is often oversimplified as simply “mycelium plus grain.” But that misses what actually happens during fermentation.
We cultivate mushroom mycelium for use in functional mushroom supplements through a long, carefully controlled fermentation process on organic brown rice for our brand, Host Defense® Mushrooms™.
It’s similar in principle to familiar fermented foods such as tempeh or koji. The food source isn’t simply added to the finished product as a filler. Instead, microorganisms act upon and transform it through fermentation, creating something chemically different from what was there at the beginning.
Our research has demonstrated that extracellular metabolites produced by mushroom mycelium transform the rice during fermentation, creating new immune-supportive bioactive compounds that are not present in plain, unfermented rice.*
Additional in vitro studies using human cell models have also shown that the mushroom mycelium and myceliated substrate in Host Defense® functional mushroom supplements work cooperatively when kept together in the finished product, suggesting complementary biological activity when both are present together.*
That’s why every Host Defense supplement includes both the mushroom mycelium and the fully transformed myceliated substrate. For Host Defense, the finished fermented mycelium ingredient is intentional. By design, it is the material we produce, test, and study.*
*These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.