Monotub

What you need

• , 54–80 litre opaque or painted storage tub
• , Rye berries or wild bird seed, 3–4 kg
• , Co coir, 650 g brick
• , Vermiculite
• , Gypsum
• , Pressure cooker
• , Polyfill and a hole saw, or filter patches
• , Liquid culture or grain spawn

Procedure

1. 01

   Prepare grain

   Simmer rye until the grains are hydrated but not split, drain thoroughly and surface-dry. A split grain releases starch, which is what bacteria colonise. University spawn labs also mix powdered lime (calcium carbonate) and gypsum (calcium sulfate) into the hydrated rye and measure the water instead of judging it by eye; Penn State's spawn lab uses 1/2 tsp lime and 1/4 tsp gypsum per 50 ml of rye in a 250 ml flask, with 60 ml of water for dry grain that is autoclaved in the flask (not simmered grain, which already holds water). Those amounts are for lab flasks, so scale them to your batch.

   Soak

   12–24 hours cold, or simmer 15–20 min

   Target moisture

   Grain bends but does not burst under thumb pressure

   Drain

   30–60 min until surfaces are matte, not wet

   Watch out: Wet grain surfaces are the number one cause of grain jar contamination.

2. 02

   Sterilise grain

   Load jars two-thirds full with a filter or micropore gas exchange, and pressure cook. Penn State's spawn lab autoclaves rye at 121 °C for 35 minutes in 250 ml flasks and 45 minutes in 1000 ml flasks; jars heat through more slowly than small flasks, which is why the jar time below is much longer. Check that your cooker holds pressure for the whole run.

   Pressure

   15 psi

   Time

   90 minutes

   Fill

   2/3 jar maximum, to allow shaking

3. 03

   Inoculate and colonise grain

   Inoculate in still air or in front of a flow hood. Shake the jar once colonisation reaches roughly 30%, to distribute growth points and cut total time roughly in half. Do not shake earlier, a young culture shaken apart may not recover.

   Liquid culture

   2–4 ml per quart jar

   Shake at

   25–35% colonised

   Temperature

   24–27 °C

   Full colonisation

   10–20 days

   Watch out: A jar with an off smell, or any colour that is not white, does not go into the tub. One bad jar contaminates the entire bulk substrate.

4. 04

   Prepare bulk substrate

   Co coir and vermiculite, pasteurised rather than sterilised. Pasteurisation deliberately leaves beneficial organisms that compete with moulds; full sterilisation creates an empty niche that the first contaminant to arrive owns outright.

   Coir

   650 g brick

   Boiling water

   4–5 litres

   Vermiculite

   4 litres

   Gypsum

   1 cup

   Pasteurise

   Pour boiling water on, seal, leave 6–8 hours

   Watch out: Field capacity again: squeeze a handful, one or two drops should emerge. A stream means it is too wet.

5. 05

   Spawn to bulk

   Mix spawn through substrate in the tub, level without compacting, and leave to colonise fully in the dark with the tub sealed. A higher spawn ratio colonises faster and gives contaminants less time.

   Spawn ratio

   1:2 spawn to substrate by volume

   Depth

   10–15 cm

   Temperature

   24–26 °C

   Colonisation

   7–14 days, sealed, dark

6. 06

   Case and fruit

   Once the surface is fully white, introduce fresh air and light. Holes at substrate level with polyfill give passive exchange; the tub does the work from here.

   Holes

   5 cm, 2 per long side at substrate level

   Temperature

   21–24 °C

   Humidity

   85–95%

   Light

   12h indirect

   Pinning

   5–10 days after fresh air introduced

   Watch out: Opening the tub repeatedly to look at it dries the surface and delays pinning. Leave it alone.

7. 07

   Harvest

   Harvest as the veil tears, before the cap flattens and drops spores. Spore drop in the tub reduces subsequent flushes and makes a mess of the surface. Twist and pull rather than cutting, so nothing is left to rot.

   Harvest cue

   Veil torn, cap still convex

   Flushes

   2–4, every 7–10 days

Troubleshooting