Grain Spawn is one of the most common techniques to propagate mycelium into a sterilized grain. Once grain spawn has been fully colonized by mycelium, it is ready to be transplanted into a mushroom growing substrates.
Many different grains will work with this technique, with organic rye berries, wheat berries, brown rice, corn, and even birdseed being some of the most popular choices.
You will need the following equipment to propagate grain spawn.
1. A container for the grain spawn that can survive sterilization. For most home mycologists this is either glass canning jars with modified lids, or special-purpose mushroom grow bags. Both the jars and the bags are suitable for surviving pressure cooker environments.
Both the glass jars and the mushroom grow bags have several essential features to make them suitable for use for inoculating grain. (1) They can survive the high temperature of a pressure cooker at 15 PSI (2) There is a “self healing” port to inject live culture from a sterilized syringe to prevent contamination from being introduced in the inoculation step. (3) There is a “fresh air exchange” hole that allows air but not microbes to pass through. This allows for filtered air to enter the bag which accelerates the mycelium colonization rate.
2. An appropriate grain, I have the best luck with whole rye kernels, commonly known as “rye berries.” Try to purchase rye suitable for food use, as cheaper suppliers of bulk grain will often come with impurities such as wood chips, dead bugs, etc that introduce unnecessary variables into your grain spawn. If you only have access to low quality grain, then wash it a bit and try to filter out any non-grain materials.
3. A pressure cooker that can hold 15 psi. I usually aim for 90 minutes, but if you are sterilizing larger quantities of grain you may need to go longer to be safe.