Puzzling taste change

[Hank Matty]

Fetzer Gewurztraminer '98 was opened at dinner Tuesday. Two glasses were enjoyed despite a taste somewhat too strong and "hard". The remainder was left in the bottle on its side in the refrigerator. Friday, the bottle was finished at dinner. The taste was much improved: more mellow, "soft", plus a bit sweeter.

I hope someone more knowledgeable will explain the change.