9:17 old bottles. The “bottles” were actually “wine-skins.” An old wineskin would retain on itself the yeast organisms that produce fermentation. Thus the fresh new wine, recently squeezed from the grape harvest into old wineskins, would soon start fermenting. The gas so produced could even generate sufficient pressure to cause the wineskins to burst.
9:17 both are preserved. Normally the “new wine” was fresh grape juice, and they wanted to preserve its health-giving freshness as long as possible.