Thanks for the thoughts and observations.
I figured it was contaminated. All the bottles are this way, so it was either this way in the fermenter and I didn’t notice it (possible, I suppose, but it was in there 5 weeks with an intact blowoff tube in a jug of starsan) or it was something in the siphon-bottling bucket-spigot-wand system. I boiled the priming sugar a good 10 minutes and it stayed covered until it was tossed in, so I doubt I got it there.
I use Starsan, and as far as I can recall the usual protocols were followed, Starsanning the bottling bucket, siphon, tubes, wand, etc, but I had some help this time around, and I’m sure not going to point fingers at her, because, well, I’m not that big an idiot, even if I have managed to bottle myself an unintentional Lambic.
I took apart the bottling wand last night and soaked it, since it seemed a likely culptrit, as well as other stuff, using PBW, figuring that the most likely thing is that I had some gunk somewhere I didn’t notice and it didn’t sanitize. I’ve got spare, new gaskets for the bottling spigot, so I’ll swap a new one in there next time around and I’ll give all the stuff a good PBW soak first, followed by a starsan soak, and throw out anything that looks old and beat up, though I don’t have much that fits that description, having done this for 2 years.
Well, I guess we all get one o’ these sometime.
The only other contamination I’ve gotten (noticeable anyway) in 20-some batches was pretty obvious, at least to my wife, who happened to open a couple of Belgians that geysered all over the place, producing a nice, black sludge. In that case, it was easy to see some crusted-on gunk in the bottles that we somehow missed. But that was only a couple of bottles. They managed to find both of them that night.
Whatever’s in here isn’t producing much CO2 at least yet. This ale remains English flattish, which is fine by me. In the meantime, the beer still smells and tastes fine, so I’ll keep swilling and keep it all in the fridge. FWIW, when I first noticed this, wondering if it was somehow yeast that floated up, I tipped each of the bottles a couple times to mix it in. Whatever’s in there that grew the gunk up top in only a few days doesn’t seem to have started growing new gunk on top, at least not quickly enough to notice.