Yellowish green powder on stored dry runner beans

Hello, some time in the last one month my stored 2023 fall harvest of dry runner beans have developed a coating of yellowish-green powder. (See photos.) I rinsed it off (easily) and cooked, ate it, and survived, but I'm curious to know what this is, if it will eventually ruin the beans or their usability as seed. Interestingly, this hasn't yet happened to the remains of my fall 2022 harvest. Any info will be greatly appreciated.

How do you keep them stored? What are the chances there are bugs living in there and when they burrow into the bean, it creates that yellow bean flour/frass?

Some of the 2023 harvest is in a plastic jar with a plastic screwtop and the rest in a glass jar with a metal screwtop. They seem secure enough. Did not notice any bugs. The 2022 harvest (which is unaffected) is in a tupperware one shelf over.

i'm pretty sure it's bug frass or drilled out bean innards. soak some up and you'll see some floaters and round holes in the beans, i bet.

i've had this happen so many times, no matter how well i think i've cared for them. usually some are still viable. i think you can pop the beans in the freezer to kill off any living insects.

Thank you all for sharing your insights and experience with this. I went through the harvest looking for the bigger beans without the yellow powder to save as seeds and noticed a few with holes in them in the process. I'm a bit surprised that I didn't see more beans with holes given how much yellow powder there is.

That’s unfortunate! Try putting any undamaged beans in cold part of freezer for a week, in hopes of killing any remaining bugs.

Mk Neal wrote:That’s unfortunate! Try putting any undamaged beans in cold part of freezer for a week, in hopes of killing any remaining bugs.

Any chance that any residual moisture in the beans might damage them from being frozen? Or that doesn't happen if the pods had dried and the beans feel hard?

I test moisture with a hammer. Hit a bean and if it turns to dust and gravel, it's safe to freeze. If it mushes, even a little, it needs to be dried more first. (I think I got that from one of Carol Deppe's books.)