How to Pasteurise Straw for Mushroom Cultivation (Beginner-Friendly Guide)
If you’re just getting into mushroom cultivation, you’ll quickly learn that straw is one of the best and most accessible substrates for growing species like oyster mushrooms. But before your mycelium can take over the straw, you need to give it a head start by pasteurising the material.
Unlike sterilisation, which kills everything, pasteurisation uses heat to reduce harmful organisms while keeping beneficial microbes alive. The result? A healthier, faster colonisation process and better yields.
Here’s a simple, step-by-step method to prepare straw at home.
What You’ll Need
Wheat, rye, or oat straw
Large pot, barrel, or cooler
Thermometer (range 140–176 °F / 60–80 °C)
Mesh or laundry bag (optional, but makes handling easier)
Clean water
Step 1: Chop the Straw
Start by chopping your straw into pieces about 2–5 cm (1–2 inches) long. This gives the mycelium more surface area to colonize and reduces the risk of contamination. A pair of garden shears works fine, but a weed trimmer in a barrel is a fast low-tech hack.
Step 2: Pre-Soak (Optional but Helpful)
Soak the chopped straw in cold water for a few hours (up to overnight). This helps soften the fibers, making it easier for heat to penetrate evenly during pasteurisation.
Step 3: Pasteurise
Now for the critical step:
Heat a large pot or drum of water to 65–75 °C (150–170 °F).
Submerge your straw completely (mesh bags are handy here).
Keep the straw at this temperature for 60–90 minutes.
Important: Don’t let the water go above 80 °C (176 °F) — too hot and you’ll sterilize the straw, wiping out helpful microbes you actually want to keep.
Step 4: Drain and Cool
Once pasteurization is complete, remove the straw and let it drain until it reaches field capacity. In other words: if you squeeze a handful firmly, only a few drops of water should escape, not a steady stream.
Spread the straw on a clean surface (or keep it in bags) until it cools to room temperature.
Step 5: Inoculate
Mix your cooled straw with mushroom spawn (typically 5–10% by wet weight). Pack the mix into grow bags, buckets with holes, or trays. From here, keep your project in a warm, dark, and clean space until the white mycelium spreads throughout the straw.
Final Thoughts
Pasteurizing straw might sound technical at first, but it’s a beginner-friendly skill that you can easily do with household tools. Once you master it, you’ll have a reliable substrate for growing delicious mushrooms at home.
