have had similar problem, I'm hoping I got it fixed...
my beers were going extremely astringent, (I think this is the correct term - though acrid could be the same thing) and more so with age.. like a couple of months, and sometimes had to chuck it...
this was happening with AG's and partials.. (the problem shouldn't be as bad with kits, but apparently makes a difference)
answer (I hope) I found on this site somewhere was to watch mash pH... my water was ph 8 going in, and this ain't a good thing.. so the answer was to put acid in the water... to ph6 with mash water and sparge...
there are a few ways to do this...
the problem doesn't affect dark beers so much, because dark grains bring pH down more.. so pH adjustment is often not necessary at all...
the result for me... smoooooth drinking beer so far... I have a recipe often repeated so far, and the version that had the ph adjusted water is just sooooo much nicer than any of the other versions...
you might think that pouring acid into a brew might not taste too good, but in my case, improved it outta sight... the acid made the beer taste a lot softer, smoother, tastier... !!! - I wouldn't have believed it until I gave it a go... am not sure how long this will last, as I have only started to do it in the last month, so am waiting, but the improvement in the beer is huge, so far... most of my non adjusted beers are getting guzzled as quickly as possible, and I reckon a lot will just end up down the sink...
mate... check your water pH... somewhere on this site someone has made suggestions for different types of brewing, but believe me, it has revolutionised my beer...
Cheers, best of luck, Organo