The duration given for the Tears of Wine spell is how long the bonus to Intelligence and Wisdom-based spells lasts after taking a drink. The wine or mead itself lasts as long as it would if it had been produced naturally.
At least that's the normal workings of the spell, though I can understand why you would want to change it for balance reasons. For the sake of simple logistics, such as the times when Zaia uses it to produce wine or mead for those aboard Marcella or living in Wayfarer's Respite, could we instead change it so that the beverage produced by the spell persists for somewhat longer, such as 1 hour per point of Zaia's Intelligence bonus plus 1 per Alchemist level, while the regular duration remains the time the bonuses last after drinking it?
If the stuff would regularly last 7 hours (his +4 INT bonus plus 3rd level), that would be plenty of time for people to drink whatever he produced, be it when we're at sea, having a feast back at Wayfarer's Respite, etc., without changing the necessity of producing less per casting if we want it to be permanent. This would be a better fit based on our previous use of the wine, since there has been mentions of it being shared among Marcella's crew and that of the Pride before we returned to Orinilu, and that would have been very difficult to manage if the stuff only lasts 30 minutes at Zaia's current level.