Last night I bottled a Barley Wine (12%, tasted great). It had been in the Secondary fermenter for about 10 weeks.
After racking it to the bottling bucket I noticed about a 2 square inch patch of black 'stuff' on the top of the fermenter. It's an enclosed opaque plastic fermenter so I could only see it through the plastic. It was at the top, above the beer, but went down to the top of the beer.
I tried cleaning it with hot water and it didn't come off, I used a carboy brush, and some came off, and now my brush is stained black (jet black). I have had it sitting in a weak bleach solution for 24 hours and some of it is still there, as though it has impregnated the plastic.
Anyone ever seen any black growth in their fermenters? I've never seen anything like this before. I drank some of the Barleywine last night, and it didn't kill me so I guess it is OK.
One thing that concerns me is that I had thought this beer had finished at 1.018 (10.5% abv) 10 weeks ago. When I came to bottle, I was surprised to find it was down to 1.010 (12% abv). I'm wondering if I have something that has been slowly eating the sugars, and might be a concern for bottle bombs; some of these bottles will still be around this time next year..