> Secondary fermentation after the wine was bottled. I'll let one of the
wine
> chemists here give you the technical aspects but easy explanation is that
there
> was still active yeast cells and sugar of some type in the wine when it
was
> bottled. At least that's my understanding.

Seems likely. It would appear that this secondary fermentation destroys some
of the complexity of the one, apart from adding unwanted bubbles.

Cheers!

Nils Gustaf