by Christopher Weeks on Mon Oct 08, 2018 7:52 am
1) We can't possibly know. It might be kahm yeast, which is technically a yeast, but normally it appears when lactobacteria have dropped pH enough and it isn't what's used to ferment alcohol. It might be something else.
2) I'm not sure. If it were my project, and I didn't detect off smells or tastes, I'd assume it was safe, if not ideal, and keep going. Our nose is a pretty finely-tuned instrument for detecting danger, but of course, we can't be sure. I'd add some sugar and a known yeast source -- raisins or even a commercial yeast packet depending on your goals and priorities and agitate until it gets to bubbling and then put it back under the airlock.
I've fermented some pretty funky stuff. And I've not always trusted that it's 100% safe. When I have something like that, I eat a very little bit and wait 48 hours. Then I eat a good amount -- a spoonful or a whole fruit or whatever, and wait another 48 hours. And if I don't get sick, then it's safe to serve to family and guests. As a parent, in a case like this, only one of us eats it first during this field-testing period so that if one of us gets sick, the other one is still up and about. The happy moral of the story is that even when stuff was so funky that we threw it in the compost instead of eating it, no one has ever gotten sick from my ferments.