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Monotub

7 to 11 weeks

intermediate

Grain spawn into a bulk substrate in a plastic tub. Yields an order of magnitude more than PF Tek for roughly the same work, and demands better sterile technique because a contaminated grain jar can take the whole tub with it.

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.

    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.

    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

What you seeWhat it isWhat to do
Whole tub greened over within days of spawningA contaminated grain jar went in.Nothing to do now. Next time inspect each jar in good light and smell it before it goes near the tub.
Mycelium stops at the surface and grows no pins for two weeksOverlay, a dense mycelial mat forms when fresh air exchange is too low and humidity too high.Increase fresh air exchange sharply. Scratching the surface lightly can trigger pinning.
Pins form then abort, turning grey then blackHumidity or fresh air swung sharply, or the surface dried.Remove aborts, stabilise the environment. Aborts are normal in small numbers.
Substrate is soggy, mycelium is patchy and slowSubstrate above field capacity.Not fixable mid-run. Measure by the squeeze test next time rather than by volume of water.
Tiny flies around the tub, and pitted stemsFungus gnats or phorid flies. Larvae eat mycelium and vector contamination.Yellow sticky traps, seal the holes with polyfill properly, and harvest the flush early. An infested tub rarely recovers.

Sources

  1. [1]Shroomery cultivation archives
  2. [2]Stamets & Chilton, The Mushroom Cultivator (1983)