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Preparing Grain Spawn

Overview

The function of grain spawn is kind of like a sourdough starter. Once you have mycelium thriving in a prepared grain you can add some of it to a prepared substrate material to grow it into a final form. First you order a syringe of mycelium cultures, then prepare some grain, like rye or brown rice, then squirt some of the mycelium cultures into the grain. After about 10 days it will hopefully be thriving and ready to add to some prepared substrate and start the growth process.

Cultures

I order a syringe of cultures from Root Mushroom Farm. There are many other sources online but I tried this first and it's been a solid product. I get a 10cc syringe of reishi mushroom cultures. Reishi are fast growing and provide a sturdy structure for making. I've read that oyster mushrooms also grow robust mycelium so I would like to try that sometime.

  1. Choose your grain: I've tried rye, brown rice, and millet. I ordered 2 lbs of rye online as it's not available in a local store. The resulting spawn has larger grains which can affect your growing outcome in terms of the thickness of the mycelium structure. If you want a thinner form, a smaller grain could be better. Brown rice is a good size grain and is readily available. Millet is even smaller.
  2. Soak grain for 12-24 hours: This is not a hard duration, the grain just needs some time to absorb water.
  3. Boil grain: About 20 minutes is good, not enough to completely open to the point where you would for a meal, but enough to swell and soften up. It's okay if some grains open, though.
  4. Add to pasteurization jars: I use canning jars with the two part lid. First drain the grain. "Field capacity" is the term I've heard used; "the amount of soil moisture or water content held in the soil after excess water has drained away," but applied to the grains. Add the grain to jars, just below the top. Cover the jars with aluminum foil and secure the foil by screwing on the rim of the lid so the foil is exposed. Then poke a few holes in the foil so pressure doesn't build up.
  5. Pasteurize: I place the jars on a vegetable steamer in the pressure cooker with water below. Soon after the valve emits steam the indicator pops up and steam stops coming out, showing that the pressure is high enough for pasteurization to begin. This video explains this process. I got mold in many of my grains and substrates at first because I didn't understand the pressure cooker system. I was turning the temperature down as soon as steam came out because I thought it was starting to pasteurize at that point, but instead I was preventing it from reaching pasteurization temperature. So understand your pressure cooker.
    I pasteurize the grain from 60-90 minutes.
  6. Cool down: Let the pasteurized grain cool down before inoculating with the cultures. You can spread it out on parchment paper, being careful to sterilize any utensil you use with rubbing alcohol, or just leave it in the jars until it cools down enough to handle.
  7. Inoculate: I add the grain to a quart size ziplock bag, loosen it up, then squirt about 2cc's of liquid cultures into the grain on top. I don't shake it up at this point to mix it in, but leave it in a concentrated area on top. Poke a few holes in the top of the bag with the syringe needle and place it in a dark place at room temperature.
    After 3 or 4 days you should see some white areas starting to spread on top. This evidence of mycelium growth may take longer to show. It may be sooner if room temperature is warmer, or longer if it's cooler.

    Mycelium growth in millet after 6 days

    Mycelium growth in faro after 7 days
  8. Leave it to grow: The mycelium will grow best in a dark, room temperature environment. It should stay moist so you want to see condensation droplets on the bag. Once it takes hold it will slowly spread throughout the grain, eventually permeating all of it. You can also break up the grain once it has grown through say half of the bag to get it to spread out. I've seen videos of spawn operations in which they put several bags in a rotating bucket to mix the spawn and encourage it to spread more quickly. This growth period can last from 2 weeks to a month and when it's grown through the whole bag it's ready to be used in a substrate.
  9. Mistakes and mishaps: I've made many mistakes! Hopefully you can learn from them.
    • Don't wait too long to inoculate the grain. One time I pasteurized grain and ordered the cultures on the same day, so my grain sat for a week before I inoculated it. While the mycelium did spawn I also got some mold so that batch failed.
    • The grain spawn can last a while before being used in a substrate but not too long. After a few weeks the grain basically starts to ferment. In some batches with rice it started to smell like sake. In a batch of faro it started to smell like beer. The mycelium will still grow as the grain sugars convert to alcohol but if it the alcohol gets too concentrated the mycelium will die. That happened in one of my batches over a long weekend when I couldn't check it. The sake smell was very strong and the mycelium had completely disappeared.
    • What happens if you don't pasteurize the grain? I tried and instead of mycelium you get mold. Here is what happened to a test batch of faro. It's clear that it's mold because it's more diffuse and growing on top rather than throughout, and grey rather than white.

      ***MOLD!! not mycelium***