Glossary

Every term this site uses without stopping to explain it. Definitions are written to be useful at the bench rather than technically exhaustive.

Abort also: Aborted pin

A pin that stops developing and dies back. Usually a response to a change in humidity, temperature or fresh air rather than a disease.

See also Pinning , Primordia

Agar also: MEA, Malt extract agar

A gel made from seaweed, used as a growth medium. Mycelium grown on a clear plate can be inspected for contamination and cut cleanly, which is why agar work is how cultures get cleaned up and kept.

See also Culture , Isolate

Biological efficiency (BE) also: BE

Fresh mushroom weight as a percentage of dry substrate weight. 100% BE means one pound of fresh mushrooms from one pound of dry substrate — a good but not exceptional result for most gourmet species.

See also Flush

Bulk substrate

The low-nutrition, high-volume material that colonised grain spawn is mixed into for fruiting — coir, straw, or manure-based mixes. Low nutrition is the point: it gives contaminants less to work with.

See also Spawn , CVG , Field capacity

Casing layer

A thin layer of moist, non-nutritious material — usually coir, peat, or a 50/50 mix — applied over fully colonised substrate. It holds water at the surface where pins need it and helps trigger even pinning.

See also Pinning , Bulk substrate

CO₂

Carbon dioxide, produced by respiring mycelium. High concentrations signal 'buried' to a developing fruiting body, which responds by extending its stem and suppressing its cap.

See also Fresh air exchange (FAE)

Colonisation

The period during which mycelium grows through and takes over a substrate. Everything before fruiting. Measured in days and the stage where most of a grow's time is spent.

See also Mycelium , Spawn

Contamination

Any organism in your substrate that isn't the one you put there. Usually a mold or a bacterium, and usually a symptom of a sterilisation or technique failure rather than bad luck.

See also Trichoderma , Sterilisation

Culture

A living sample of a specific fungus, kept on agar, in liquid, or on grain. A culture is a clone; a spore print is a genetic lottery.

See also Agar , Liquid culture , Isolate

CVG also: Coir vermiculite gypsum

Coco coir, vermiculite and gypsum — the standard bulk substrate recipe. Cheap, consistent, pasteurises easily, and holds water well.

See also Bulk substrate , Field capacity

Field capacity

The maximum water a substrate can hold without free water draining out. Test by squeezing hard: a few drops means correct, a stream means too wet, nothing means too dry.

See also Bulk substrate , Hydration

Flow hood also: Laminar flow hood

A fan and HEPA filter that pushes a laminar stream of sterile air across a work surface. Makes transfers and inoculations near-foolproof, and is the single biggest equipment upgrade for anyone doing volume.

See also Still air box (SAB) , Sterile technique

Flush

One wave of mushrooms from a colonised substrate. Most substrates give two or three, each roughly half the size of the one before.

See also Biological efficiency (BE) , Fruiting conditions

Fresh air exchange (FAE) also: FAE

How often the air in a fruiting chamber is replaced. Controls CO₂ concentration, which controls stem length and cap development. The single most misunderstood variable in fruiting.

See also CO₂ , Fruiting conditions

Fruiting body also: Sporocarp

The mushroom itself — the short-lived reproductive structure the mycelium builds to release spores. Not the organism, and not where most of a grow's attention goes.

See also Mycelium , Primordia

Fruiting conditions

The combination of temperature, humidity, fresh air and light that signals a colonised substrate to fruit. Introducing them is a deliberate act, not something that happens on its own.

See also Fresh air exchange (FAE) , Pinning

Grain spawn

Sterilised grain fully colonised by mycelium, used to inoculate bulk substrate. Rye, millet, oats and wild bird seed all work. Nutritious, which is why it must be sterilised rather than pasteurised.

See also Spawn , Spawn rate , Wet spot

Gypsum

Calcium sulphate. Added to substrate at around 5% of dry weight to buffer pH, add calcium, and stop grain kernels sticking together.

See also CVG , Grain spawn

Hydration

Getting water into a substrate before treatment. Too little and colonisation stalls; too much and you create the anaerobic pockets contaminants exploit.

See also Field capacity

Hyphae

The individual thread-like filaments that make up mycelium. Singular: hypha. What you see as a white mat is millions of them.

See also Mycelium

Inoculation

Introducing culture into a sterilised substrate. The moment of highest contamination risk in the whole process.

See also Sterile technique , Liquid culture

Isolate

A single genetic line selected from a multi-spore culture and propagated on its own. Isolating is how you get consistency between grows instead of variation.

See also Agar , Culture

Liquid culture also: LC

Mycelium grown in a sterilised sugar solution. Fast to inoculate with and easy to multiply, but it cannot be visually checked for bacterial contamination the way agar can.

See also Culture , Agar

Master's Mix

Equal parts hardwood fuel pellets and soy hull pellets by dry weight, hydrated to about 60% moisture. The standard high-performance substrate for wood-loving gourmet species.

See also Sawdust , Supplementation

Monotub

A plastic storage tub modified with holes for passive fresh air exchange, used as a combined colonisation and fruiting chamber. The most common bulk setup for home growers.

See also Fresh air exchange (FAE) , shotgun-chamber

Mycelium

The branching network of hyphae that is the actual fungal organism. It spends weeks digesting the substrate; the mushroom is a brief reproductive event at the end.

See also Hyphae , Fruiting body , Colonisation

Pasteurisation

Heating a substrate to 65–75°C for 60–90 minutes to reduce, not eliminate, competing organisms. Enough for low-nutrition substrates like straw and coir. Not enough for grain.

See also Sterilisation , Straw

Pinning

The formation of primordia on a colonised surface. Triggered by a change in conditions — usually a drop in CO₂, a temperature shift, or light.

See also Primordia , Fruiting conditions

Primordia also: Pins

The tiny knots of tissue that become mushrooms. Also called pins. Extremely vulnerable to drying out.

See also Pinning , Abort

Rhizomorphic

Mycelium that grows in visible ropey strands rather than an even fluff. Often taken as a marker of vigour, though the correlation is weaker than commonly claimed.

See also Tomentose , Mycelium

Sawdust

Hardwood sawdust, usually from fuel pellets. The substrate for wood-loving species. Supplemented sawdust must be sterilised.

See also Master's Mix , Supplementation

Spawn

Any colonised material used to inoculate a larger substrate. Usually grain, sometimes sawdust or plug dowels.

See also Grain spawn , Spawn rate

Spawn rate

The ratio of spawn to bulk substrate, by volume. Higher rates colonise faster and resist contamination better. 1:2 to 1:4 is typical.

See also Spawn , Bulk substrate

Spore

A single reproductive cell. Two compatible spores must fuse to produce fertile mycelium, which is why spore-grown cultures vary and cloned cultures don't.

See also Culture , Isolate

Sterile technique

The set of habits that keep contaminants out during transfers: alcohol on everything, minimal movement, flame-sterilised tools, not talking over open jars.

See also Still air box (SAB) , Flow hood , Inoculation

Sterilisation

Eliminating all living organisms, including bacterial endospores. Requires 15 psi for 90–150 minutes depending on volume. Required for grain and supplemented sawdust.

See also Pasteurisation , Wet spot

Still air box (SAB) also: SAB

A clear plastic tub with arm holes, used to create a space with no air currents for transfers. Cheap, effective, and adequate for most home-scale work.

See also Flow hood , Sterile technique

Straw

The classic low-cost substrate for oyster mushrooms. Needs pasteurisation, not sterilisation. Hot water, lime bath and cold fermentation all work.

See also Pasteurisation , Bulk substrate

Supplementation

Adding nitrogen-rich material — bran, soy hull, gypsum — to a substrate to raise yields. Every point of added nutrition also raises contamination risk, which is the trade.

See also Master's Mix , Sterilisation

Tomentose

Mycelium growing as a fluffy, even, cottony mat rather than in strands. Normal for many species and not a fault.

See also Rhizomorphic

Trichoderma

The green mold. Starts white, turns forest green as it sporulates, and outcompetes mycelium that has been slowed down by something else. Not treatable.

See also Contamination , Sterilisation

Wet spot also: Sour rot

Bacterial contamination of grain by Bacillus species. Grey gluey patches and a sour smell. Almost always traceable to a pressure cooker that didn't hold 15 psi long enough.

See also Grain spawn , Sterilisation