Interactive lesson

Oyster mushrooms on straw, step by step

Interactive lesson: from a bale of straw to a basket of oysters — chopping, hot-water or lime pasteurisation, bags, colonisation, fruiting and harvest.

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The whole lesson as text

1. Straw

Straw is both food and home for the mycelium.

What you need — For one bag: 3–3.5 kg of dry straw (10 kg wet), 0.5–1 kg of grain spawn and a clear bag. It gives 2–2.5 kg of mushrooms in 2–3 flushes.
Good straw — Wheat or barley, this year's, kept dry. Old, rained-on or mouldy straw won't do.
Chop to 3–10 cm (1–4 in) — Chopped straw is easier to pasteurise and packs better. A strimmer in a 200 L (55 US gal) drum, a forage chopper or a hatchet on a block.
Mask and goggles — Chopping raises dust full of mould spores. Work outdoors, with an FFP2 (N95) mask and goggles; people with asthma should leave this job to others.

Why: Good straw is golden yellow, dry, smells of straw and isn't dusty. Grey, dusty straw, or straw that smells mouldy, already carries millions of mould spores, and no pasteurisation reliably saves it.

It is easiest to do 2–4 bags at once: the pot is the same and the risk is spread.
Don't use straw from a sprayed field, or hay: mycelium grows poorly on sprayed straw, and hay moulds quickly.

2. Hot-water pasteurisation

Pasteurising kills most moulds but leaves some useful microbes.

Heat the water — Heat the water to 70–75 °C (158–167 °F). When you sink the straw in, the temperature drops to 65–70 °C.
Submerge the straw — Weigh the straw down in its net or sack with a stone or grid so it is completely under water.
Hold for 1–2 hours — Hold at 65–75 °C (150–165 °F) for 1–2 hours. Measure in the middle of the pot, not at the edge; below 60 °C, add heat and extend the time.
Lift out and drain — Lift out with a fork or in the net, wearing gloves to the elbow, never by hand from the water. Drain for 1–3 hours on a clean rack, covered with a cloth.

Why: That is why straw is not boiled: boiled straw gets contaminated faster than pasteurised straw. For every kilogram of dry straw allow roughly 20–25 L of water.

Water at 70 °C causes serious burns within seconds. Stand the drum on a level, firm base, with children and animals well away.
An electric immersion heater in a drum only with an RCD (GFCI in North America) and a sound cable.