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How to Prepare Grain Spawn

Grain spawn is cooked, sterilized, and cooled grain that you inoculate from myceliated petri dishes or liquid culture (LC).


I sterilize grain spawn in canning jars with wide mouths (for ease of transferring) that have been fit with airport lids


Many cultivators, including myself, soak the grains for ~10-24 hr. before cooking them (in fungus-friendly water). Keep this in mind in your work flow.

Stage 10-11 of Grain Spawn Recipe. The grain spawn has been prepared, soaked, cooked,  cooled, and equally(ish) filled into my 5 quart-sized mason jars with airport lids.  Now ready to be covered in a foil cap and sterilized in the PC.
Stage 10-11 of Grain Spawn Recipe.

Above image: Stage 10-11 of Grain Spawn Recipe. The grain spawn has been prepared, soaked, cooked, cooled, and equally(ish) filled into 5 quart-sized mason jars with airport lids.

Now ready to be covered in a foil cap and sterilized in the PC.

Grain Sourcing

Commercially common grains used as spawn are usually rye grain (also called rye berries), millet, or wheat berries. Home cultivators have also seen success using spelt, popcorn, whole birdseed, sorghum (milo). All of these grains are preferred due to their low levels of nitrogen (N) and ease of preparation. Many other grains are too high in N, which can lead to overheating during mycelial growth or high contamination rates. Whatever the grain, higher vitamins and minerals will support a flourishing mycelium. A smaller grain provides more points for inoculation and will ease the growing of the mycelial web. I use rye grain, otherwise known as rye berries. As with any step of cultivation, if you can acquire local and sustainably grown, organic, and regeneratively farmed grain -- this is where it's at! Mushroom cultivation that's beneficiary to the environment instead of damaging to it is our beautiful responsibility. If you can grow your own grain spawn, this is even cooler. Inoculum Sourcing

Inoculum is the fungal tissue used to inoculate a substrate, like grain spawn, or used to infect a host organism. You can source your inoculum in a variety of ways:


  • Cloning local mushrooms in agar or liquid culture. Local species and strains are going to be most resilient, strong, and adapted to your growing conditions.

  • Buying or trading liquid cultures from local mushroom cultivators or websites.

  • Buying or trading agar petri dishes from local mushroom cultivators or websites.

It's wise to know where your fungal strains are coming from to ensure strong and reliable strains -- just like knowing where your food comes from. Once you've grown or acquired a culture of healthy, vigorous, and competitor-free inoculum, the next step is to inoculate this mycelium into some grain spawn that has been cooked, sterilized, and cooled. I use liquid cultures (LC) in mason jars with airport lids so I can easily extract myceliated liquid with my syringe and then inject it into my grain spawn jars. Through LC method, I don't have to use a sterile lab environment or glovebox to expand the inoculum into the grain spawn, easing the work flow by quite a few steps. By using airport lids, I keep my grains pawn jar lids closed, in a safe sterilized container, and inoculate the grain using my LC via syringe needle. Preparing Grain SpawnThe highest quality spawn are grains that are properly prepared and loved prior to sterilization. Grain prep guiding principles:

  1. Grains should be al dente! Just like your Italian noodle, grains should be just right -- not too hard and not too soft. They've gotta be just right. The key to look for is if your grains have no center, they are good to go! This makes them fully saturated and supple enough for mycelium to penetrate and digest. 

  2. Grains should not be overcooked or too soft. There should be a minimum of sprouted or burst kernels after sterilizing in the pressure cooker (or other sterilization method). Overc