Earlier this year, Mr Wort Hog brewed up a Maibock for the first time. Everything went well and, given that he is a brewing perfectionist, fermentation and lagering seemingly went without a hitch. We have a couple of freezers in the basement hooked up to temp controllers to keep fermentation & lagering temperatures stable, but something still went wrong: it tasted fruity.
Fruitiness in beer is typically from undesired esters created during fermentation, a byproduct of ethanol meeting fatty acids. The potential for ester creation can be increased by underpitching yeast (causing fast yeast growth which generates esters), not giving your yeast enough oxygen, or starting off with a high-gravity wort. Whatever the reason, we definitely had some esters on our hands.
Turns out it was a bigger success than I imagined - this was a good beer and we went through over 3 gallons of it at the last brew day. Moral of the story: unless your beer is completely ruined, consider changing it. Add some fruit or vanilla extract. Soak a few oak chips in it. Pour in a bottle of bourbon. Toss some mulling spices into some vodka, let them soak for a week or so, then add the vodka to the beer. If you're planning on tossing it anyway, there's no harm in trying to save it from the drain.