What is the difference between fruiting body and mycelium?

What a fruiting body is

The fruiting body is the mushroom itself. It is the part that pushes up out of the log or the growing block, and it is the part you would recognize on a plate. A lion's mane fruiting body is the shaggy white ball. A reishi fruiting body is the hard reddish shelf. When a grower harvests that structure, dries it, and mills it, the powder that comes out is made of the mushroom and nothing else.

Fruiting bodies take time to produce. A crop has to run through its whole cycle before anything can be picked, and it is harvested by hand and dried before milling. That time is the main reason a fruiting body powder usually costs more per ounce than the alternative below.

What mycelium on grain is

Long before a mushroom fruits, it lives as mycelium, a network of fine white threads that runs through whatever it is growing on. Mycelium is the organism, and the fruiting body is what the organism eventually produces in order to spread its spores. Both are real parts of the same fungus.

A common way to make mushroom powder at scale is to grow mycelium on a bed of sterilized grain, usually oats, rice, or sorghum, and then dry and grind the whole block once the threads have run through it. The mycelium in the finished powder is genuine mushroom mycelium. What comes with it is the grain, because there is no practical way to separate threads that have grown into a grain kernel from the kernel itself. Products made this way are often described on the label as mycelial biomass, mycelium on grain, or myceliated grain.

Why the difference shows up in the container

The two are not interchangeable by weight. In a powder grown on grain, a share of the finished weight is the substrate the mycelium grew through, and that share shows up on analysis as starch. How large that share is varies with the producer and the method, so the honest summary is that a meaningful portion of the powder is grain rather than mushroom.

That is worth knowing for beta-glucans, the compounds a lot of people are reading labels for in the first place. Beta-glucans sit in the cell walls of the fungus and are concentrated in the fruiting body, so a powder carrying a lot of grain carries fewer of them per scoop. It also changes the arithmetic when you compare prices. Two containers only compare like with like when both hold the same kind of material, which is why price per ounce on its own can be misleading.

How to read a supplement label

The front of a container is marketing copy. The supplement facts panel and the ingredient line are where the useful information lives. Four things are worth checking.

• The ingredient line is where the answer usually is, so look there for the words "fruiting body". Some labels write it as "fruiting bodies only" or name the species followed by "mushroom", which mean the same thing.
• If the ingredients say mycelium, mycelial biomass, myceliated oats, or myceliated rice, the product was grown by the second method and the grain is part of what you are buying.
• The word "extract" describes how the material was processed rather than which part was used, so an extract can be made from either one. A label can say "extract" and still owe you an answer about the part.
• If nothing on the panel names the part at all, that is worth an email to the company before you buy. A producer who uses fruiting bodies has every reason to say so on the label.