I was browsing through the Cleric spells a minute ago and rediscovered Enhance Water, which allowed the castor to turn a pint of water into wine or beer with varied appearance. I know that the spell can be used as a relatively discrete and effective way to deduce if the drink you have has been contaminated, but can you sell the drink for a profit?
Yes, you can.
There's no reason to assume that it can't be sold, after all.
However, the potential to make a profit is very low. Assuming level 20, you can convert 20 pints of water into beer per cast of the spell. Ale (beer) is priced at 4cp per mug (pint). Since you are selling the beer, you get half the market price: 2cp. 20*2cp = 40cp, or 4sp, for 20 pints of beer. At level 20, you can cast ~36 level 1 spells per day (not counting bonus spells from a high WIS score or your domain slots), so if you spent all of your slots to prepare this one spell 36 times and cast it 36 times, you could make, at most, 14gp and 4sp per day. One day of adventuring nets you far more than that at level 20 (even at level 1 a full day of adventuring nets you more than that), so why even bother?
To clarify: the reason the cleric could cast Enhance Water 36 times is because the rules allow a caster to prepare lower level spells in higher level spell slots. Clerics at level 20 receive 4 slots (+1 domain slot) per spell level, not including bonus slots granted from high WIS scores, so the assumption is that for maximum profit, the cleric would prepare Enhance Water in every available spell slot, all the way up to 9th level spells.
Sure, why not? It's non-magical beer or wine; if you can find a buyer, you can sell it.
Of course, it's worth coppers to the pint, so probably nobody will want it. An innkeeper is unlikely to be interested in anything you can't deliver barrels full of and if people in the street want a drink they'll probably just get it a tavern instead of from some weird guy selling half a jug of whatever he has in there.
As noted, you can sell this for half the market price, as you can do with any item you make or otherwise acquire which is valued below twice the settlement you wish to sell it in's purchase limit. In addition to cheap drinks like common ales, your spell can specifically create wines, beers, and meads, and is definitely able to create some other unspecified alcoholic beverages, while not necessarily being able to create any arbitrary alcoholic beverage. Whiskeys and such thus may be possible to create but also may not be, at the discretion of your DM.
Regardless, the most expensive mundane base alcoholic drink I am aware of in Pathfinder is Sealord Wine1, which is a wine and so within the category of definitely producible drinks. Sealord Wine sells for 15 gp per 1/2 pound, which means you can sell it for 7.5 gp per 1/2 pound, or 22.5 gp per Imperial Pint2(Wines, predictably, have approximately the same density as water). At level 1 you're looking at something like 67.5 gp/day assuming you don't specialize in this at all.
Some people argue that, on account of it being expensive, Sealord wine must be high quality wine, and the spell cannot make a Sealord wine of middling quality. This reasoning is, of course, wrong for a variety of reasons, not least of which that Sealord wine is not, in fact, high quality wine, but if your GM subscribes to such reasoning, you can get by nearly as well by substituting in the next most expensive broad category of alcoholic beverage your DM's houserules allow.
Pathfinder actually officially uses US wet pints/gallons/etc instead of Imperial ones, so if you're constrained to those, you may make somewhat less coin. A US gallon is derived from the wine gallon, so that would actually make some sense here, whereas the Imperial Gallon is derived from the larger ale gallon.