Green Apple Flavour in Keg

[blisterman]

Just racked my beer after four weeks, into a keg, connected it to the gas tank and taps. Stupidly never tasted it after fermentation.
Had a sip of the flat beer from the taps, and there's a very distinct Green apple flavour.
Had this once with a bottled beer, and it went away after a couple of weeks, but I'm not sure about pressurised kegs. What's my best course of action?

Leave the Keg pressurised and chilled?
Depressurise the keg but keep it chilled?
Depressurise the keg and keep it room temperature?
Rack it back into a fermenting bucket and leave it to ferment a few more weeks?

 

[ArtVandelay]

I'd leave it hooked up to get it pressurized in the kegerator for a couple weeks. After that point if its still green, pull it out of the kegerator and let it age some more still pressurized at room temperature.

 

[blisterman]

Should I pitch more yeast to encourage further fermentation and conditioning?

 

[ArtVandelay]

After 4 weeks its likely not going to ferment any further so no point adding yeast especially if you are force carbing. Just let it be for another month

 

[blisterman]

Ok left it for over two months, had a sniff. Good god, it smelled bad. Really solventy. It was also the consistency of maple syrup. Ended up throwing the whole batch away.

What could be the cause of that?