For The Love Of Port

Maybe a dumb question , but why do some bottels have a double capsule while others have only one?

Pretty common to have a thick outer capsule, with a thin inner one.

My guess is that the inner capsule is put on when the bottle is corked, the outer when it is released from the cellar/lodge for sale. That doesn't explain why, however.

Perhaps the second is to make it look nice upon release, while the first is to merely keep some of the cellar schmutz off the end of the bottle after being bottled?