Stout has gone bitter

[Aussmeister]

Hi all just wondering if anyone can shed some light as to why my Irish stout has gone bitter. I kegged it on Sunday and gassed it up at pouring pressure, 12psi. On Wednesday night I got stuck in and it tasted ace. Now come Friday it's got a bitter taste to it. Its never happened before as I make this quite often it's drinkable but I can't work out what's happened

 

[emnpaul]

What did you eat before you had the stout today? Something sweet?

 

[Aussmeister]

ok my bad in a slightly drunken state I'd swapped lines the night before and had forgotten, lines had some pale ale in it...Doh :blush: All is well again.