How to test spawn quality?
Spawn ages and loses its strength with time. How do you define the power of your spawn after it has been stored for a while?
Take the following steps to test your spawn quality:
1. Take a petri dish which has been prepared with MEA mixture (for sale at Mycelia for 0.5 €/pc). Open it under a sterile environment (preferably a laminar air flow) to avoid contamination. Contamination will give false results.
2. Put a few spawn kernels onto the petri dish with a sterile tool - e.g. a spoon sterilized under a naked flame.
3. Roll the kernels around under the petri dish, still under LAF. Close the petri dish and label it.
4. Let the petri dish mature at a beneficial temperature for the mycelium. For Oyster mushroom or Shiitake, 20°C for a five days to one week is fine. There should be mycelium growth from the kernels and from the places where the kernels have rolled over the agar medium.
5. Results. The amount of mycelium growth after a week should give you some indication about the strength of the spawn. Old spawn will also have the capacity to overgrow a substrate just like fresh spawn, but it will grow much slower. The same accounts for those few kernels on the petri dish. If the growth is swift and profuse, your spawn is still very active. If it hasn't done anything in - say - five days, discard your spawn/plugs. It may still be active, but old spawn is slow so infections get all the time they need and it's better to be safe than sorry.
There is a second, cheaper technique you might use, which goes as follows: Take a sample from each bag you wish to use. Take a clean (!) plastic container, put a pile of wet paper (toilet paper, kitchen paper) and put the spawn/plugs on top of the paper in a warm but shady place. The mycelium should be visibly growing into the paper in five days to one week. Be warned that this technique is much more risky and may give false results!