Grain spawn is the process of expanding mycelial mass. It strengthens the mycelium to a point where it is ready and strong enough to be put into bulk substrates. The grain serves as supplement for the mycelium, as well as, the vehicle for even distribution into the substrate.

Grain selection

Rye, wheat, millet, sorghum, corn, oats, brown rice and wild bird seeds may all be used as grain spawn. Many growers select rye grain as it has a great moisture capacity and is easy to process, however it can be difficult to source reliably.

Wheat is much more readily available and perform very similar to rye grain but requires more attention when processing. Millet offers more points of inoculation but it is very pricey and not suitable for all mushroom varieties.

Here at Naturemade we use 100% Biodynamic Western Australian wheat.

Grain preparation

There are many methods to prepare your grain depending mostly on which grain you are going to use. With wheat and rye, for instance, ideally you soak your grains for 24hrs, discard the water and boil them for 20min or until you see their colour changing and notice the grain absorbing the water.

What you want is for the grain to hold as much water as possible inside the grain whilst avoiding it to get cooked. Once it looks well hydrated, drain the water and let it cool down.

To test for its water content you can place few grains on a paper towel to see how wet it is. It should leave a very small or no water mark on the paper and the grain should be still slightly hard and not cooked.


Once your grain has been drained and cooled down, put it into filtered bags or jars and sterilise it for at least 120min in an autoclave or pressure cooker. Depending on the size of your bags you may need to increase your sterilization time. At Naturemade we make 1.7kg grain spawn bags and sterilise them for 180min.


Once grains are cool, inoculate them with liquid culture or a slice of a clean myceliated agar in a sterile environment, preferably in front of a flow hood. Make sure you shake bags and/or jars thoroughly before placing them in the dark for colonisation (incubation).


Ideally you want to keep them at a dark room with some circulating air but nothing major. Spawn tends to grow well and strong when kept around 21-24°C. At such temperatures contaminants are kept in check while mycelium thrives.

You may choose to shake your bags or jars once when they are around 70% colonised. Just make sure you shake it only once and also keep bags from touching each other in order to avoid overheating.

Spawn to substrate

Once bags and/or jars look totally white and without any sign of contamination they are ready to be put into a substrate to colonise and give you beautiful and healthy mushrooms or may also be used to colonise more grains, a process called grain-to-grain or G2G.

This is a good form to exponentially multiply spawn, which then can be used one last time to colonise even more grains or to inoculate the mushroom substrate.

It is recommended that no more than 3 transferences is to be made before using the spawn for colonisation of substrate (mix where the mushrooms will grow).


  • Grains: rye, wheat, millet, oats, wild bird seeds, corn, sorghum, milo.
  • Soak grains for 24hrs.
  • Boil/simmer grains for 20min till it has soaked as much water as possible (avoid cooking the grain).
  • Drain grains.
  • Pack in filtered bags or jars.
  • Sterilise for a minimum of 180min @ 15psi.
  • Inoculate with liquid culture or slice of myceliated agar.
  • Adhere to sterile techniques.
  • Incubation temperature: 20-24°C
  • To be kept in the dark with some re-circulation of air (small fan inside chamber, draw, box, cupboard).