Although Cordain repled that he didn't think vinegar was a significant factor
before neolithic times I can not imagine that all of the grapes or apples
were consumed so quickly that the naturally present surface blush of yeast
did not proceed to fermentation to vinegar and that this wouldn't have been
available and used as a flavoring. Catching the process while alcohol was
present is also quite probable - after all cattle are fond of eating fallen
partially fermented apples to the point of intoxication. i.e., stumbling in
the orchard!