Growing mushrooms on expired flours

While cleaning out the back of the pantry I found several pounds of whole grain flours (wheat, oat, etc) that expired a while ago. I don't think they're suitable for human consumption anymore, but I'm wondering if they could be used to grow mushrooms.

But I'm not finding anything online about doing this. I do see people propagating mushroom spawn on grain, but this is usually with the whole grain, which you soak, sterilize, and innoculate. If you tried adding water to flour, you'd get dough, and I don't think it would work.

Does anyone have any suggestions on this?

Really great question Joshua!

My thoughts are to not grow on just flour, but some mixture of flour and straw, flour and wood chips, maybe flour lining the inside of a log.

If you are wanting to do this inside I might consider getting a 5 gallon bucket full of straw and thoroughly wet it down and pack it in just as you would for any other indoor mushroom project.  But maybe after getting it all wet, sprinkle in the expired flour so that it sticks to the straw.  At that point you can spread in the spawn and maybe just a little more flour to top things off.  Hopefully the flour will act as an accelerant for the already fast decomposing straw and get you your mushrooms that much faster.

I think this is worth some experimenting, so please let us know how things work out.

Eric

The "PF Tek" for growing "special" mushrooms uses brown rice flour on vermiculite as a growing media, 2 parts vermiculite, 1 part flour, 1 part water, mixed and then sterilized.

That's... kind of a specialized case though. I think you'd need to put it on some sort of bulky, less nutritive media, maybe wood chips or sawdust, and you'll want to STERILIZE, not just pasteurize, as the tiniest contamination will rip through the highly nutritious flour, and even then, you'd want a very aggressive mushroom like oysters.

The only thing I could find is a study of inky caps on flour as a medium.

https://pubmed.ncbi.nlm.nih.gov/35433389/

This means that SOME mushrooms might find flour to be a good medium. This would require some experimentation on your part if you wished to see. Perhaps you could use it as a part to a mix of things.

Worst case, flour is great in a compost pile.

Nick Williams wrote:you'll want to STERILIZE, not just pasteurize

Do you have any guidance on the difference here? Is it just a matter of hotter or longer in the pressure cooker, or some essentially different procedure?

Joshua Frank wrote:

Nick Williams wrote:you'll want to STERILIZE, not just pasteurize

Do you have any guidance on the difference here? Is it just a matter of hotter or longer in the pressure cooker, or some essentially different procedure?

Basically, pasteurization kills most live organisms, weakens the rest, and doesn't do anything to most spores. Need 167 F for a sustained period (like a couple hours) to prepare substrate. That's fine for low nutrient density substrates and aggressive mycelium, because bacteria (for instance) digests cellulose a LOT slower than say... oyster mushrooms, so the mushroom mycelium can outcompete any contaminants.

When you have something like grains, or flours, there's a lot of starches and sugars that are easily digestible by your competing microorganisms, so you need to sterilize (i.e. kill EVERYTING, including spores) the media. That's generally considered achieved at about 250 F.

Nick Williams wrote:That's generally considered achieved at about 250 F.

I don't have a pressure cooker, but I do have an InstantPot, which is said to hit 10 to 12 psi above sea level pressure and reach 239°F to 245°F.

Would it be sufficient, do you think, to leave it at that temperature for 90 minutes or so?

Joshua Frank wrote:

Nick Williams wrote:That's generally considered achieved at about 250 F.

I don't have a pressure cooker, but I do have an InstantPot, which is said to hit 10 to 12 psi above sea level pressure and reach 239°F to 245°F.

Would it be sufficient, do you think, to leave it at that temperature for 90 minutes or so?

Yeah, that will do it.