I have been told that hops bitterness is cut about in half after six months in the bottle. I think that is why IPA's are not really aged a long time? Anyway I brewed a partigyle a while back and it was VERY bitter ( REALLY good with salty food) I popped one open a few minutes ago and it is REALLY smoothing out nicely and the bitterness is noticibly less. Another 3-4 years and it might even be considered a smooth quaffer lol!!!