Agar work

Agar is where cultivation stops being a gamble. On a clear plate you can see what you have — mycelium, bacteria, mold, all of it — before committing grain, time and space to it. Every serious grower ends up here, and most wish they had arrived sooner.

Why bother

Three things agar does that nothing else does:

Contamination becomes visible early. A bacterial colony on a plate is obvious at 48 hours. The same contamination in a liquid culture syringe is invisible until it ruins twelve jars of grain.

You can clean up a contaminated culture. Cut a piece of clean mycelium from the leading edge of a partly-contaminated plate, transfer it, and repeat. Two or three passes usually recovers a clean line from a marginal one.

You can isolate. Spore-grown cultures are populations. Selecting one sector and propagating it alone is how you get consistency, and it can only be done on a solid medium.

Making plates

The standard recipe, MEA — malt extract agar:

20 g light malt extract
20 g agar agar
2 g nutritional yeast (optional, improves growth noticeably)
1 litre water

Whisk cold, then heat gently while stirring until it clears. Decant into bottles no more than two-thirds full, cap loosely, and sterilise at 15 psi for 30 minutes.

Pour at around 55–60°C — hot enough to flow, cool enough not to produce a lid full of condensation. Pour in a still air box or in front of a flow hood, lifting the dish lid only enough to get the stream in.

A litre fills roughly 25–30 standard 100mm plates.

Working cleanly

The technique matters more here than anywhere else, because the reward for sloppiness is immediate and visible.

Still air box or flow hood. Not the kitchen counter.
Scalpel sterilised to glowing, then cooled on clean agar before touching mycelium. A red-hot blade kills what it touches.
Alcohol on everything — the outside of the dishes, your gloves, the work surface, the bottle you are pouring from.
Do not talk over open plates. Speech aerosolises a remarkable amount.
Move slowly. Fast movement creates air currents, and air currents carry spores.

Transferring

Cut a small wedge — 5mm is plenty — from the leading edge of a healthy colony. The edge is the youngest, most vigorous tissue and the least likely to carry anything picked up during earlier handling.

Place it mycelium-side down on fresh agar. Seal the plate edge with parafilm or micropore tape. Label it: strain, generation, date. You will not remember.

Incubate at 70–78°F in the dark. Most species cover a plate in 5–10 days.

Isolating

From a multi-spore plate, different genetic individuals grow as visibly distinct sectors — differing in density, growth rate, texture, or the presence of rhizomorphic strands.

To isolate: pick the sector you like, transfer from well inside it, and repeat two or three times until the resulting plate is uniform. That uniform plate is a single genetic line, and it will behave the same way every time you use it.

What to select for depends on what you want, but in general:

Fast, even radial growth
Dense rhizomorphic character in species that show it
No sectoring or patchiness on the third-generation plate

Selecting for appearance on agar is an imperfect proxy for fruiting performance. The only real test is fruiting the isolate, which is why serious isolation work takes months rather than weeks.

Reading a plate

What you see	What it is
Slimy, glossy, wet-looking patches	Bacteria
Coloured circular patches with defined edges	Mold — see diagnostics
Fluffy white advancing evenly	Healthy mycelium
Ropey visible strands	Rhizomorphic growth
Clear zone between two colonies	Two incompatible individuals meeting

That last one is worth knowing: a visible line where two colonies meet and stop means they are genetically incompatible. Where they merge invisibly, they are compatible, and this is the basis of compatibility testing.

A clean, isolated plate goes to either liquid culture for volume, or straight to grain for a single run.