Stewing with Apple Cider Vinegar I'm working on making a long cooked version of a stew which uses apple cider vinegar as part of the flavor.

I was wondering what happens to the flavor of the vinegar when it's cooked for a long time. I have technical constraints and it needs to cook for about 24 hours, and I was wondering if it would lose the flavor.

Also I was wondering if adding vinegar is pointless, seeing as long cooked stews tend to get very brown, it'll end up being a very alkaline environment, and maybe that would cancel out the acidity.
An acid in a stew serves much the same purpose it would in a marinade. It aids in the tenderizing (typical 'stew meat' is cut from inferior cuts of the beef and can be tough) and balances the flavors. (As such I would disagree with @lspare about adding it "at the end", it needs time to do it's work) 

Browning is a separate issue. Browning is the result of the Maillard reaction and should occur when stew meat is seared prior to being incorporated into the stew. In a stew the 'cooking temperature' is never above 212°F (100°C) and this will not 'brown' the meat.