My cider has a slight vinegar taste!!! It's still in the carboy, and I dropped some pectic enzyme in there to clear it out, but I just gave it a quick taste and it's got a slight undertone of vinegar taste!
You sure it's not a sour/bitter taste? As long as your carboy was topped up, or had a nice thick Co2 blanket over it, it shouldn't be acetobacter. One of my ciders this year that was very green tasted a bit like vinegar, but it aged right out.
If you keg, I just lightly flow some Co2 from my tank into the carboy for 3 to 5 seconds. Is this still in the primary? How much headspace are we talking?
The man who intoxicates himself on bad whisky is sometimes moved to kill his wife and set his house on fire, but the victim of applejack is capable of blowing up a whole town with dynamite and of reciting original poetry to every surviving inhabitant.
– “A Wicked Beverage,” New York Times, April 10, 1894
Is it the carboy that you posted in the current "Cider Photo" thread? If so, that's a lot of head space and I am not sure what to do short of the kegging idea.