The first time this happened I was doing Uncle Jessie's recipe, it was my 5th or 6th batch. For this batch, I had tried grinding/blending the cracked corn in a food processor before adding the sugar and water. I wanted to see if it affected the flavor. I use a stainless steel keg as my fermenter, and I used to cover it with a bunch of plastic wrap. I switched to using just a towel hoping the CO2 would keep out any bad stuff. I'd read on here that others do the same thing. When the ferment was more or less done, maybe day 4, I saw all of this on top of the wash. I skimmed it off and did the stripping run anyway. Never had any issues, even during the spirit run, everything came out great.
The second time I saw this was doing an all grain, cracked corn, wheat, and malted barley. I boiled the corn for an hour, at 160 added the wheat, at 150 I added the malt. I wrapped the boiler with towels to keep it warm, and let it steep covered overnight. At 95F I pitched the yeast. On about day 4 again, I saw all of this stuff. Again, I covered the keg with a towel. I have to admit that I would peek in about once a day, I may have let some bad stuff in.
