He didn’t say his school let them do it.
Mine didn’t have time to ferment; raccoons drank it, or hornets found it.
My wife cleans and refills her hummer feeders every other day. She only fills them about 1/3 full, the dozen or so hummers we get do a good job of almost emptying them. The only problem we have is a couple very aggressive hummers. They will spend more time chasing away other hummers than they do feeding.
Having worked in insurance, I hope many can learn something laterally from this thread. Not only is yeast floating in the air, so is mold. Wet a food source, bread, paper, pretty much anything organic and it will grow. So all these companies putting petri dishes to get it to mold proves nothing. We can’t give you mold free air, and mold in your air is not damage. And even if it were, it’s excluded. A combination of people being lured by unethical, tricky contractors, and the fact that they often view insurance as their enemy, makes this a problem that anyone, if they ever looked at a pollen/mold report should immediately dismiss. Of course you can grow mold in a petri dish.