The strangest bottle defect I've ever had

A couple nights ago, I pull the cork on a bottle of 2008 Dominique Piron Beaujolais-Villages. The cork comes out intact.

I tilt the bottle over my glass to pour. Nothing comes out. I tilt more until the bottle is upside down. Still nothing comes out of the bottle. I look back into the neck to see if the cork had broken off in the bottle. It hadn't.

I look more closely under light. There is a solid black disk sitting at the bottom of the neck. I get out a knife and poke it. It cracks. I poke it more and it cracks some more. This time, I can pour the wine through the hole in the disk.

I determined that the solid disk was a precipitation of tartrate crystals with pigments, giving the illusion of a solid disk, which it no doubt had formed. I can only imagine that the crystalization had occurred while the bottle sat upright in a box or on the shelf prior to purchase last year.

FWIW, the wine had also undergone secondary fermentation and was sour and undrinkable.

My guess is the secondary fermentation took place with the bottle upside down in the case, thus forming the disc of crystals and tannin pigments against the surface of the cork. Then the bottle was stored upright on the shelf, drying out the cork, causing it to shrink and separate from the disc. But, who knows - I've never heard of such a thing.

Not totally unthinkable, I’ve seen lots of corks with tartrate crystals stuck to them. Like Howie said somehow the crystal “freed” themselves from the cork surface and gravity didn’t have time to get it to the bottom of the bottle. (Very possible the corkscrew itself just barely making it through the cork could of “freed” the crystals still intact clogging the neck of the bottle).

Salute

There were no crystals on the cork and the cork was not penetrated at the bottom. The cork was not dried out.

My best guess is that the bottle was stored upside down, and bottled before M/L was finished. The sediment plug was a combination of solid particulates of various sorts and dead M/L bacteria.

I once saw a bottle of Ch. Rieussec with huge dead fly in it.

The wine was delicious.