A large share of the mushroom supplements sold in the United States are not mostly mushroom. They are fungal mycelium grown on sterilised grain, with the grain milled into the finished powder because separating the two at scale is impractical. Published comparative testing has commonly reported that material in the range of roughly 35 to 60 percent residual starch, with beta-glucan content down around 1 to 5 percent.
Nothing about that is illegal, and in most cases nothing on the label is technically false. It works because of one word — "polysaccharides" — and because no federal rule says the word "mushroom" on a supplement label has to mean the mushroom. The fix is a single number on a certificate of analysis, and this post explains which number, how the test works, and what to do when a supplier will not produce it.
Three materials, sold under one word
| Material | What it is | Typical beta-glucan |
|---|---|---|
| Fruiting body | The mushroom itself — the reproductive structure, dried and usually extracted | High. Commonly reported in the tens of percent for extracts. |
| Mycelium on grain | Mycelium grown through sterilised rice or oats; the whole colonised mass is dried and milled together | Low, with a large residual starch fraction from the substrate |
| Liquid-fermented mycelium | Mycelium grown in liquid culture and separated from the growth medium before drying | Variable, but the substrate is not in the finished powder |
All three can lawfully be described using the name of the species. Only the first is a mushroom in the sense a customer means when they buy one.
What mycelium actually is, fairly stated
Mycelium is the vegetative body of the fungus — a network of fine filaments that does the actual growing, feeding and, in commercial cultivation, most of the work. It is real fungal tissue, not a counterfeit, and it contains fungal compounds. Some constituents are found predominantly in mycelium rather than in the fruiting body: erinacines in lion's mane are the standard example, and the corresponding hericenones are associated with the fruiting body instead, which we cover species by species in the functional mushroom buyer's guide.
So the problem is not mycelium. Stated precisely, the problem is grain substrate sold as mushroom. A producer who grows mycelium in liquid fermentation, separates the biomass from the medium, and can quantify what ends up in the jar is selling a defensible product. A producer who grows mycelium through a bag of brown rice, dries the whole bag and mills it is selling you rice with fungus on it.
Why the grain stays in
Solid-state cultivation on grain is cheap, fast and reliable. Sterilised rice or oats are inoculated, the mycelium colonises the substrate over a few weeks, and the result is a solid block of grain bound together by fungal filaments.
At that point the mycelium is physically inseparable from the grain. There is no practical industrial process for pulling the filaments out of a colonised grain mass. So the entire block is dried and ground, and the resulting powder is a mixture of fungal biomass and unconsumed starch — weighted heavily toward the starch, because the mycelium consumed only part of it and the growing cycle is deliberately short.
The finished product is then labelled with the species name and, often, an extract ratio. Both are accurate as far as they go. Neither tells you the proportion.
The word that hides it: "polysaccharides"
Here is the mechanism, and it is worth understanding in full because it is used everywhere in this category.
Beta-glucans, the structural polysaccharides in fungal cell walls, are the accepted measure of genuine mushroom content. But starch is also a polysaccharide. It is a glucan too — an alpha-glucan, differing from beta-glucan in how the glucose units are linked.
So a product guaranteeing "over 50% polysaccharides" may be making a true statement about a powder that is largely rice starch. The measurement usually behind such a claim is a crude gravimetric one: precipitate the polysaccharide fraction with alcohol, dry it, weigh it. That method captures starch along with everything else and cannot distinguish the two.
A polysaccharide percentage, on its own, carries almost no information about a mushroom product. When you see one presented as the headline quality figure, the correct response is not to be impressed. It is to ask what the beta-glucan number is.
Alpha-glucan versus beta-glucan: the discriminating test
The test that settles it measures both glucan types. The standard enzymatic assay for fungal material determines total glucan, measures alpha-glucan separately, and reports beta-glucan by difference. Because alpha-glucan in a mushroom powder is overwhelmingly residual starch from the substrate, the alpha figure functions as a direct measurement of how much grain is in the jar.
That is why the two numbers have to appear together. A beta-glucan figure alone can still be presented flatteringly. Beta-glucan reported alongside alpha-glucan tells you the whole composition in two lines:
- High beta-glucan, low alpha-glucan. Fruiting body material, doing what it says.
- Low beta-glucan, high alpha-glucan. Grain substrate with fungal tissue through it.
- Only a "total polysaccharide" figure. The question was not answered.
Ask for it in exactly those terms: beta-glucan and alpha-glucan, quantified separately, on a per-lot certificate from an accredited laboratory. Accreditation matters here as much as the number does, for reasons we set out in how to read a certificate of analysis. Very few brands in this category publish the split. The ones that do are telling you something real, and the ones that decline are usually declining for a reason.
What the published testing shows, and what we will not claim
The figures at the top of this post — roughly 35 to 60 percent starch, beta-glucan around 1 to 5 percent — come from comparative testing published by ingredient suppliers specialising in fruiting-body material, and from comparison data published by at least one retailer that runs its own testing.
Three qualifications, because this is precisely the kind of number that gets repeated until it hardens into folklore.
First, those are ranges across a set of products, not a measurement of any particular one. Second, the most-cited sources are commercial suppliers of fruiting-body material, which means the finding, however well documented, comes from parties with a direct interest in it. That does not make it wrong — the underlying chemistry is not seriously disputed, and the general direction has been corroborated by others — but you should know it. Third, we have not run this testing ourselves, and we are not going to attach these percentages to any named brand on the strength of someone else's laboratory work.
What we will say is narrower and, we think, more useful: any product whose certificate reports a large alpha-glucan fraction is largely substrate, and that is a measurement anyone can commission. We would rather publish a defensible general finding with its provenance attached than a precise-sounding number we cannot stand behind. The same discipline governs everything on our lab results page — a panel only clears what it looked for, and we say what ours covers and what it does not.
Label phrases that should slow you down
- "Polysaccharides >50%" with no beta-glucan figure anywhere on the label or certificate.
- "Myceliated biomass," "mycelial biomass," "full spectrum," "whole fungus." All are accurate descriptions of mycelium on grain. None mentions the grain.
- "Cultivated on organic brown rice" in the ingredient statement. This is the honest version, and it is telling you the rice is in the product.
- An extract ratio with no plant part. "10:1" from fruiting body and "10:1" from colonised grain are not comparable claims.
- A proprietary blend of six species with one combined milligram total. The composition is being withheld by design.
- Common name only, no Latin binomial. Species identity is the floor, not a bonus.
Several of these follow the same pattern as the certificate problems described in why we do not carry blue lotus: nothing stated is false, and the document still fails to answer the question you asked.
Why the labelling persists
Because there is no federal rule requiring the word "mushroom" on a supplement label to mean the fruiting body. Guidance exists within the trade, but trade guidance is voluntary and binds nobody. In the absence of a definition, a truthful ingredient statement and a truthful polysaccharide figure can coexist with a product that is mostly starch — and the market has had no reason to change, because almost no buyer asks for the alpha-glucan number.
That is genuinely fixable by customers. It is one question, and a supplier either answers it or does not. It is also the question we ask before we carry anything in this category; Botanical Blends is a distributor and retailer, so the certificate is the whole of our leverage, and the standards we apply are listed in our FAQ.
Frequently Asked Questions
Is mycelium on grain a scam?
Not in the legal sense, and we would not use that word. It is a cheaper material sold under a description that is technically accurate and practically misleading. The failure is disclosure, not adulteration — which is exactly why a composition test resolves it and an argument does not.
What beta-glucan percentage should I look for?
There is no single correct threshold, because it varies by species and by whether the product is a dried powder or a concentrated extract. The comparison that matters is beta-glucan against alpha-glucan in the same report. A product where alpha-glucan substantially exceeds beta-glucan is mostly substrate regardless of what the headline number says.
Does an "extract" label mean the grain was removed?
No. Colonised grain can be extracted just as fruiting body can, and the extract inherits whatever was in the starting material. The extract ratio describes concentration, not purity, and it is meaningless without knowing what was concentrated.
How do I ask a brand about this without getting a marketing answer?
Ask one narrow question: "Can you send the per-lot certificate showing beta-glucan and alpha-glucan quantified separately?" Not "is it high quality," not "is it third-party tested." The narrow question has only two possible outcomes, and both are informative. Our guide to reading a certificate of analysis covers what to check once it arrives, and the functional mushroom buyer's guide covers what to buy in each species.
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. For adults 21+. Legality depends on the specific formulation and applicable state law — check the rules where you live. Nothing here is legal advice.