It may not be a storage issue and may not be an indication that
anything is wrong with the wine. The bottle was probably stored upside
down and the sediment collected on the cork. Just wipe it off the cork
or the neck of the bottle.
You didn't mention how the wine tasted. So, how did the wine taste?

On Apr 24, 11:05 am, wrote:
> I tried a California merlot & discovered a thick, dark residue on the
> inside of the bottle after it was corked. Ick! What is it? I
> presume this is something to do with improper storage.
>
> Thanks in advance, my fellow wine lovers!!