Acid, it may change with age. Most brews will get a lot more body through the brewing process and change considerably.
My most memorable one was a dirt cheap lemon and limeade sort of affair. Very strong, but after fermenting it was undrinkable. We racked it and hoped that would sort it. It did not, we bottled. Tasted it after a few weeks of ageing, some bottles were drinkable (though you'd only want to if you wanted to get smashed). Fast forward 4 months or so and we had ran out of booze but my pal remembered about that stuff. It turned out quite pleasant in the end. Not amazing by any stretch of the imagination, but easily drinkable and miles ahead of what it was when we made it.
Don't despair yet.