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Pasteurised straw (hot water)

Chopped straw held hot in water for an hour or two, then packed with oyster spawn.

180°F160°F
Plate 8 of 16Pasteurised straw (hot water), drawn for All the Tek.

What it is

Straw is a low-nutrient, high-carbon substrate, so it does not need sterilising. Heat knocks back competitors and fast-growing oyster mycelium takes over1.

Cornell’s guide keeps the straw at 140 to 160 °F for at least two hours, most easily by heating water and straw to 180 °F, shutting off the heat and putting the lid on1. UF/IFAS pasteurises at 165 °F for 1 to 2 hours2. Either way the straw is drained and cooled below 100 °F before spawning1.

UF/IFAS mixes in spawn at 5 to 10% of the straw, packs bags until they feel like a firm pillow and cuts 10 to 15 small crosses in two rings around each bag2.

What it suits

Oyster mushrooms. Cornell calls oysters the best species to grow on straw; other species do less well on it1.

Species notes are on the species page; for the mushrooms themselves, see Ohio Gourmet Mushrooms.

Equipment

  • Straw, shredded or chopped
  • A large pot or metal drum and a heat source
  • A thermometer
  • Oyster grain or sawdust spawn
  • Bags about 10–12 by 20–24 inches2, or buckets
  • A clean surface for cooling

Time to first harvest

About 3–5 weeks. Cornell gives about five weeks from inoculation to harvest for oysters on straw1. In the UF/IFAS guide the fruiting stage starts around three weeks after the bags go into incubation2.

Contamination and other risks

  • Green mould (Trichoderma). UF/IFAS tells growers to watch for blue, green, black or yellow spots and discard heavily contaminated bags2.
  • Insects. Straw bags need to fruit indoors because bugs lay larvae in them outside1.
  • Spawning hot straw, which can kill the spawn; wait until it is under 100 °F1.

Steps, in overview

  1. Chop. Shredded straw gives the mycelium shorter jumps and can raise yields substantially1.
  2. Pasteurise. Hold at 140–160 °F for about two hours1 or 165 °F for 1–2 hours2.
  3. Drain and cool. Spread on a clean surface until it drops below 100 °F1.
  4. Spawn and pack. Mix in 5–10% spawn and pack bags firmly2.
  5. Incubate. Dark, 75–77 °F, for about two to three weeks until white2.
  6. Fruit. Cut holes, then give about 68 °F, about 90% humidity, light on a day-night cycle and good air exchange2.

Common mistakes

  • Packing loosely, so the mycelium has gaps to cross.
  • Fruiting straw bags outdoors1.
  • Keeping a partly contaminated bag in with clean ones; UF/IFAS discards heavily contaminated bags2.

Safety

Large volumes of near-boiling water scald. Lift straw out in bags or baskets and let it cool before handling.

Oyster mushrooms drop large amounts of spores2. People with mould allergies or asthma can react strongly to mould3, and oyster spores have been linked to hypersensitivity pneumonitis in growers4.

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Sources

  1. Methods of Commercial Mushroom Cultivation in the Northeastern United States. Willie Crosby (Fungi Ally) and Steve Gabriel, Cornell Small Farms Program, 2019 (Northeast SARE). Extension publication, checked 26 October 2026.
  2. D.I.Y. FunGuide: Grow Your Own Oyster Mushrooms at Home. Hameed, Cotter, Liao and Hsu, UF/IFAS Extension (EDIS SS662). Extension publication, checked 26 October 2026.
  3. Mold. Centers for Disease Control and Prevention. Government, checked 26 October 2026.
  4. Hypersensitivity pneumonitis associated with mushroom cultivation. Satoh and Yamada, Journal of Postgraduate Medicine, 2022. Research, checked 26 October 2026.