Well they can. It's called Kahm Yeast, https://melissaknorris.com/kahm-yeast/ https://melissaknorris.com/kahm-yeast/ I typically just skim it off. And you ca

Well they can. It's called Kahm Yeast, https://melissaknorris.com/kahm-yeast/ https://melissaknorris.com/kahm-yeast/ I typically just skim it off. And you can't get botulism from fermenting. That is only in canning foods, since all the microbes are competing with each other. Good old C. botulinum can't hang.