Growing Thoughts: The Limitations of Expanding Grain Spawn
TL;DR Grain spawn has limitations due to contamination and mycelium senescence.
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Growing Thoughts: The Limitations of Expanding Grain Spawn
In the beginning of growing mushrooms, my idealistic goal was to ignore liquid cultures and agar plates and rely on grain spawn. How lovely would it have been to just throw a few myceliated grains from one colonized jar into a new jar and just make mushrooms indefinitely?
But what I ignored was the baggage you carry with you when you do grain-to-grain transfers.
Here are some axioms about the mushroom growing process that limit the possibilities of grain spawn expansion:
Every step of the mushroom cultivation process is a race against time before inevitable contamination occurs, because:
Sterilizing substrate is not literally 100% sterilizing something, it’s reducing life to an absolute minimum so mushroom mycelium can have a fighting chance for as long as possible. If you left a sealed, sterilized grain jar in a room for several months, the mold will arrive.
Mushroom mycelium is a linear extension of cells. And all sexually reproductive organisms have a shelf-life when it comes to cell division. For mycelium, this is called senescence, where a particular strain has come to the end of its life. It will grow slowly, not produce fruiting bodies, and likely have life-ending mutations.
With these mycological axioms, you can come to a couple conclusions with grain spawn expansion:
You can only expand your spawn so much before the dormant contaminants that travel with your previous grain spawn wake up, or contaminants find a way to get in during a transfer.
You can only expand your spawn so much before it dies.
You may have observed that healthy mycelium in a petri dish will work to contain and isolate some contaminations before they grow. They can be effective at this on a 2-dimensional medium like agar, but in grain spawn, mold spores will quickly branch out with new spores in every direction.
As Paul Stamets notes:
In a jar holding thousands of kernels of grain, a single kernel of grain contaminated with a mold, surrounded by tens of thousands of kernels impregnated with pure mushroom mycelium, makes the entire container of spawn useless for mushroom culture.
Grain spawn is very useful for a few generations because it is fast and convenient. But like the rest of the mushroom cultivation field, don’t go all in one technique, or else you’ll be haunted by the baggage that follows.
Grow more, and don’t become a mold farmer,
Dom
PS - Senescence occurs after 7-9 generations from the first clean culture that you use. So agar plate → liquid culture → fruiting → cloning → agar plate is the movement from the first generation to the second generations. But see how you can make so much more mushrooms with each generation: Hundreds of grain spawn jars with a liquid culture; thousands of substrate bags with grain spawn; tens of thousands of new agar plates with cloned mushrooms. This is a limitation, but boy is it one that you can delay for a long, long time.