Beer Changing Bitternes

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This is probably the third batch that this has happened to. Once brew is transfered into a keg via filter and force carbonated for a week the flavoure and bitterness is right. After about 2 weeks the beer goes extremely bitter and thick (viscosity) to the point where it becomes undrinkable. I thought it might be some sort of infection so i have pulled all of my kegs apart cleaned and put new seals in them and cleaned all of my beer lines still no luck. It only seems to be happening to my ale style beers. Dose anyone have any advice?
More details,

recipe, yeast, temps.....
If it is an infection and you are filtering, maybe its coming from the filter.
The kegs aren't freezing are they?

My first thought, too.
Just cold enough for the water in the beer to seperate into ice slush sitting on top and drawing the "beer" from the bottom.

if you've ever done an apple jack with beer, you'd recognise it...
i have experienced the same, normally a keg won't last that long to notice it but i have also noticed since i no longer filter that my beer is lasting much longer,
been on holidays and the kegs in the fridge would be easy 2 months old and ony 1/4 full. i thought it may be vinegar flies on the tap but this is not the case.
i don't want to start the filter or not debate, but i have through trial and error found what works is long conditioning at cold temps gives a better
end result for longer life kegs , i think you have to be very pedantic about oxygen and germs in the filtering process, and for me it takes up too much gas and time.
i only filter the odd brew now if my stocks run down. rinse your cleaned filter in cooled boiled water and purge filter with co2 before filtering to avoid oxidization.
Funny you say that keifer33 went and had a look inside my kegs and they are frozen is all lost what can i do? :eek:
If it's frozen the water will separate from the alcohol and you will get a concentrated brew, hence the viscosity and increase in other flavour compounds - like reducing a beef stock down and getting concentrated flavours.

Look up freeze distilling and eisbock.

Probably not lost - you could age it and try for some kind of barley wine (not speaking from experience - merely an idea). Also I think you might be able to let the kegs warm up and recover the brew as is - I'll let someone who's been in the same situation confirm though. I'd be more concerned about stopping your kegs freezing than this actual brew though.
If you let it defrost you will need to give it time to carb back up but from my experience the beer is never the same again. I had this happen a while ago after i accidentally placed the probe in the total wrong spot away from any kegs and had the keezer nearly empty. As manticle states find the problem and fix it for the next brew.
depending on how much of the concentrated part you removed, once the ice melts you could end up with a pretty watery beer.

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