Mold Killer?

A few weeks ago I was emptying out a bottle of Guinness that had, most unfortunately, gone partially to waste, and was shocked, I tell you, shocked, to see mold going into the sink.

Tonight I emptied out another bottle of Guinness, that had been sitting on my table for a good two weeks. (Yes, I know, disgusting, I agree.) No mold whatsoever.

The first bottle was Stout, I think; the second bottle was Extra Stout. Maybe the Extra has some sort of element or quality that tells mold to go shove it? I would have thought that alcohol would have done that, but apparently it doesn't work for some types of Guinness.

Having donated that profundity to your evening, I'm going to go read, and then hit the sack. Moonraker, here I come...