What Is Grain Spawn?
Grain Spawn is made from sterilised grains that have been inoculated with a live mycelium culture. These inoculated grains are consumed by the growing mass of mycelium.
The fully colonised grain spawn can be used as a starter culture for growing mushrooms. These grains are sometimes referred to as mushroom seeds due to their appearance and application.
Grain spawn contains a lot of energy for the mycelium to consume. It’s a bit like rocket fuel for mushrooms. Once it’s added to your substrate it takes off like wild fire.
Mother Nature works her magic using spores but in a controlled environment you need to tip the scales in your favour by using clean high-quality grain spawn so you are doing your best to ensure success.
Grain spawn is incorporated into a bulk substrate which is subsequently colonised by the mycelium culture. Once ready it will begin to convert the energy from within the bulk substrate into mushrooms.
A wide range of materials can be used as a bulk substrate for growing mushrooms. These include Popcorn, Rye, Sorghum, Wheat, Millet, Sawdust and many more.
Each type of grain used has pros and cons such as how long it takes to colonise, how prone it is to infection and even the size of the grain, ie smaller grains have more inoculation points when added to bulk.
In my opinion popcorn is a great grain to start with, it is easy to find, easy to work with and because it is normally food grade it is kept much cleaner that other grains which are often used for animal feed.
How to make Grain Spawn
Firstly you need a pressure cooker / canning machine / autoclave that has enough space to fit whatever vessel you will be using to make your spawn in. The pressure cooker needs to reach 15psi as at this pressure the inside will reach 121c which is the point at which almost all possible contaminates will be killed.
Spawn can be made in many vessels, all you need is it to be self contained and have some form of filter to allow for gas exchange while preventing any contamination from entering. Probably the easiest vessel is a 3T unicorn grow bag but many people also use glass jars. You can easily convert a glass jar by drilling 2 x 2mm holes in the lid, put micropore tape over each hole to act as your filter.
Now get yourself some popcorn. Rinse it a few times and make sure the water is clear. Add about a tablespoon of gypsum (if you have but it is not essential) per litre of spawn
You want to soak this overnight , this does two things, firstly hydrates the popcorn and secondly allows any endospores (a dormant tough structure made by some bacteria that is difficult to sterilise) to germinate making it easier to kill them during sterilisation.
The following day add the popcorn to a pot and simmer it for about 30 – 40 minutes. You want the popcorn kernels to get slightly soft so you can almost squish them in your figures, they will also absorb a lot of water and swell up.
While the popcorn is still hot drain it and put it in a large tray stirring it every 5 minutes or so. You want the stream to come out and dry the popcorn. It is essential to make sure the popcorn is totally dry on the outside, you can test this by taking a spoon and putting it on toilet paper, it shouldn’t leave any wet patches behind.
Now fill up your your unicorn grow bag / modified console jar about 3/4 full of popcorn ( it is useful to allow for some room so you can shake up the popcorn while it is colonising ) If using modified bottles put tinfoil over the top.
Now cook this at 15psi in your pressure cooker. Exact cooking times can vary depending on the size of your vessel, a 1l console jar should cook for about 1h45 minutes and a large unicorn bag with 3kg of spawn for up to 3 hours.
Once finished cooking let it cool in the pressure cooker until you can handle it. At this stage the corn is sterile and precautions should be made when using it such as working in from of a flow hood or inside a still air box.