Agar is where you stop being a customer for genetics and start being a keeper of them. It is also the only stage where you can see contamination before it costs you anything.
Most growers arrive here after losing a batch of grain to a liquid culture that looked fine.
What you need
| Item | Cost |
|---|---|
| Petri dishes, 100mm, 20 pack | $10 |
| Light malt extract | $10 |
| Agar agar powder | $12 |
| Scalpel and blades | $8 |
| Parafilm or micropore tape | $8 |
| Nutritional yeast, optional | $5 |
You already have the pressure canner and the still air box.
What agar gives you
Contamination becomes visible early. A bacterial colony shows on a plate in 48 hours. The same contamination in a liquid culture is invisible until you have ruined twelve jars.
You can rescue a contaminated culture. Cut clean mycelium from the leading edge, transfer, repeat. Two or three passes usually recovers a clean line.
You can isolate. Spore-grown cultures are populations with varying vigour and yield. Selecting one genetic line and propagating it alone is how you get the same result twice.
You can clone. A flush produces one exceptional fruit — faster, heavier, better formed. Cloning preserves exactly that. A spore print would not.
You can store cheaply. Agar slants keep 6–12 months refrigerated. A library of a dozen strains fits in a lunchbox.
Making plates
MEA:
- 20 g light malt extract
- 20 g agar agar
- 2 g nutritional yeast (optional, noticeably better growth)
- 1 litre water
Whisk cold, heat while stirring until clear, decant into bottles two-thirds full, sterilise 15 psi for 30 minutes.
Pour at 55–60°C in the still air box — hot enough to flow, cool enough not to condense on the lid. A litre fills 25–30 plates.
The three operations
Transfer: cut a 5mm wedge from the leading edge of a healthy colony, place mycelium-side down on fresh agar, seal, label, incubate at 70–78°F.
Clone: take a fresh mushroom, tear it open rather than cutting through the outside, and take tissue from the interior of the stem. The inside of a fresh fruiting body is effectively sterile; the outside carries whatever was in the room.
Isolate: from a multi-spore plate, transfer from well inside a sector you like. Repeat two or three times until the plate is uniform. That uniform plate is a single genetic line.
Full detail: agar work.
Reading a plate
| What you see | What it is |
|---|---|
| Fluffy white, advancing evenly | Healthy mycelium |
| Ropey visible strands | Rhizomorphic growth |
| Slimy, glossy, wet-looking | Bacteria |
| Any coloured circular patch | Mold — identify it |
| Clear line where two colonies meet | Genetically incompatible individuals |
Building a library
Keep a master you never work from and a working copy you transfer from. Every transfer risks contamination and adds a small step toward senescence.
Label everything: species, strain, generation, date. You will not remember, and an unlabelled plate is worth very little.
Store slants refrigerated. Go back to the master rather than transferring generation to generation indefinitely.
What changes
This is where cultivation becomes repeatable. Before agar, each grow starts from whatever you were sold. After agar, each grow starts from a line you selected, cleaned and kept — and the same strain behaves the same way every time.
That consistency is what makes selling possible.
After
If you want to turn this into income: selling at a farmers market.
Sources
The works this page draws on. These are references, not pinpoint citations — see how sourcing works here.
- Growing Gourmet and Medicinal Mushrooms3rd ed., Ten Speed Press1993
- Organic Mushroom Farming and MycoremediationChelsea Green Publishing2014