Grain Spawn

The following example details how to prepare 1kg of sterilised rye grain for use as growing medium in bulk spawn production. The measurements can then be scaled according to the type of container you are using for the grain. One of the simplest containers to use is a glass jar. In this example we are using 2lb jars. It is important to note that once hydrated rye grain increases in weight by approximately 30% and at least doubles in volume.

• Rye Grain 600g
• gypsum 10g
• water
• micro pore tape or cotton wool/poly-fill
• tin foil

• 5x Jar 770ml/2lb
• Drill and 6mm drill bit
• Pressure cooker


Firstly, a note on preparing you jar lids. You need to create a filtered air exchange. Do this by making a 6mm hole in you jar lid and then filling with cotton wool or cover with micropore tape.

  1. Wash the grain: you need to get all the dust and any chaff from the grain, 4 -5 washes should do the trick.
  2. Leave to soak overnight. Use enough water to cover the top of the grain by 2-3cm.
  3. Bring to boil and simmer until the rye grain is hydrated, don’t overcook, when this happens the grain kernels burst and increases the risk of contamination.
  4. Drain and steam off excess moisture. Just stir the drained cooked rye grain and allow the steam to evaporate. You want to avoid any excess moisture but at the same time, you don’t want the kernels to dry out.
  5. Sieve the gypsum onto the grain while stirring.
  6. Place into the jars. Fill only a third. In this example 200g in each jar should be sufficient. If you overfill the jars you will have problems when it comes to shaking the myceliated grain spawn.
  7. Put on the lid but don’t over tighten, with the prepared filter. Cover with the lid with tin foil. This prevents excess moisture getting into the jar during the sterilisation process.
  8. Place jars in pressure cooker, off the bottom of the pan, use an inner pan or improvise a metal spacer.
  9. Sterilise at 15psi for 90mins. Start counting when at 15psi.
  10. Once sterilised wait until the pressure returns to 0psi then carefully move the pressure cooker to sterilised work area for inoculation. Leave here until cool, about 6-9 hours.

You can now inoculate you sterilised grain with grain, agar or liquid inoculation.

For further detailed instructions be sure to get a copy of at least one of the essential mushroom grower books in our resources page.

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