How to Start Grain Spawn

The foundation of strong, resilient mushroom cultivation.

Beginner-Friendly Grain Spawn Recipes

Brown Rice Grain Spawn (Per Jar)

Ingredients:

  • About 1 cup of brown rice per quart jar

  • Boiling water

Method:

  1. Bring water to a boil in a large pot.

  2. Dump in the brown rice (~1 cup per jar you’re preparing).

  3. Boil for exactly 10 minutes — no more, no less.

  4. Immediately strain the rice and rinse under cold water for 30 seconds to halt cooking.

  5. Allow the rice to air dry in a colander for 15 minutes to remove excess surface moisture.

  6. Load into mason jars using either:

    • Upside-down unmodified lids (tightened and flipped)

    • Or modified lids with gas exchange filters

  7. Cover each lid loosely with aluminum foil to minimize moisture buildup during sterilization.

  8. Sterilize:

    • 1.5 hours at 15 PSI (pressure cooker)

    • 2 hours at ~12.5 PSI (Instant Pot or lower-pressure units)

Whole Oats Grain Spawn (Small-Scale "No-Soak" Method)

Ingredients:

  • 100g dry oats per quart jar

  • 80g water

Method:

  1. Directly pour 100g of dry oats into each quart jar.

  2. Add 80g of clean water directly into the jar.

  3. Close jars with either upside-down unmodified lids or modified gas exchange lids.

  4. Cover lids with foil.

  5. Sterilize:

    • 1.5 hours at 15 PSI

    • Or 2 hours at ~12.5 PSI

  6. Important: Perform a hot shake immediately after the pressure naturally releases.
    ➔ Shake jars thoroughly to evenly distribute moisture.
    ➔ Skipping this step can cause oats to overcook or clump.

Whole Oats (Large-Scale Traditional Method)

Ingredients:

  • Bulk dry oats

  • Water for soaking

Method:

  1. Soak oats in cold water overnight (12–18 hours).

  2. Drain thoroughly.

  3. Spread oats out to steam-dry for 30–60 minutes until surface dry but hydrated inside.

  4. Load into jars or bags (⅔ full), lid and foil, and sterilize.

✅ Traditional soaking gives you larger batch prep for commercial or large home grows.

Sterilization Essentials

Proper sterilization removes contaminants that would otherwise compete with your mushrooms. Always pressure sterilize:

  • 1.5 hours at 15 PSI (pressure cooker)

  • 2 hours at 12.5 PSI (Instant Pot)

Let the grains cool completely before inoculation to avoid killing the mycelium.

Inoculation Basics

Grain is inoculated using:

  • Liquid culture syringe

  • Agar wedges (small clean samples)

  • Grain-to-grain transfers (for scaling up)

Best Practices:

  • Always inoculate inside a still air box or in front of a laminar flow hood.

  • Flame sterilize your needle or blade before and between jars.

  • Inject ~2–5 mL per jar for liquid culture.

  • Gently shake or swirl after inoculation to distribute the culture.

Watching Colonization

  • Store jars or bags at 65–75°F in a clean, dark area.

  • Mycelium should start showing within 3–7 days, fully colonizing in 2–4 weeks depending on species.

  • Check regularly for signs of contamination (off smells, colors other than white).

Why Grain Spawn Mastery Matters

Grain spawn multiplies your mycelium, allowing you to turn a few drops of liquid culture into dozens of fruiting blocks or outdoor beds. Healthy spawn is:

  • Faster to colonize substrates

  • More resistant to contamination

  • The gateway to larger, more reliable harvests

Every colonized jar is a stepping stone toward thriving ecosystems of mushrooms — and toward becoming a confident, capable cultivator.