I had a bit of grain left during my last run, so I mixed the bits I had left.
This is interesting, actually. Over the next few months, I'll continue this experiment to see what grain mixes might work better for spawn.
While this wasn't a "proper" test, I had still hypothesized that the higher starch content in the popcorn would do better. I guess not.
I'll try and separate testing into different categories like starch content, moisture content, mycelium strain, etc. There is probably a ton more conditions to isolate as well.
I haven't tested/verified this myself but I've heard that mycelium grows particularly well on millet and rye berries. Might be a couple to add into your experimenting.
Rye is the go-to and millet has a massive amount of surface area. I know rye will work but since it is a very well established grain to use, I want to explore other options as well. TBH, brown rice has been performing very well for me in all cases as well.
I have 10lbs of millet (split into 4 bags) that is getting close to 20 days or so. It started extremely slow, but once it took hold, the colonization has increased speed exponentially. I also have to break it apart more often to get more colonies established.