Well, as a matter of fact my dad is an amateur winemaker (pretty good stuff), and "new wine" has always been the wine of this season, which has completed the vat fermentation process but has been bottled. As a general rule, it's raw but it's cheap. I think the scoffers were making fun of the apostles, as in, "these guys are a bunch of cheap drunks."
The wine would not have been put into skins until after the first fermentation, because that process produces so much carbon dioxide and general tumult that it's done in barrels or vats (probably big clay jugs in the old days). I vividly remember one hot fall afternoon when we went to church and the fermentation process overheated . . . we returned to find a river of purple running down the driveway . . . oh woe! As my dad says, he'd rather see an old lady run over by a train.
agreed ... the CO2 is the problem ... hence Jesus' illustration of new wine into old wineskins, a revelation of the mystery of the Church Age to come ... as I'm confident you're familiar with! (obviously!) ... FReegards ...