Great question Hoover and welcome to the forum

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I'm not sure how to answer it as, I think it depends. I'll have a crack though

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Okay, something that is hop-driven, like an APA, I think you would be best to knock over earlier rather than later, preferably within a few months. A lager/pilsner, if your hygiene is good, you should have no probs up to a year, at least. It will change during that time but normally for the better. Non-hop driven ales or hybrids, I'd be happy drinking up to a year. They also will change a tad (or a lot).
What I'm trying to say above is that if you put the beer into the keg well, it takes a very long time to go off. That's my main point.
My second point is that change does occur. I remember putting a beer into a show one year, some APA I think. It got a bronze or silver (that means nothing btw) but I still had the same beer in a keg a year later and it tasted nothing like an APA so I entered it as a Kolsch or something, just to get tickets to the tasting! I do remember, though, that when I made myself forget the beer was originally an APA, and just tasted it for what it was, I really liked it.
So, bear the above in mind before the next story...
A few years ago, I travelled, in the height of summer, from on side of Australia to the other in a van. I stopped in a few places for several weeks leaving several kegs, baking in my van at over 50C/122F. A few months later I arrived in Perth. I chilled the kegs and tasted the lager first thinking that would be buggered for sure. It was actually great

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I then tasted an English ale, and, to this day, I'll never understand why, but I just drank it without even sniffing it. Why did I do that? Confidence from the lager? Anyway. I nearly died

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That whole experience still annoys me as I don't know why one beer survived/improved while the other became toxic. In hindsight, I'd bet, for sure, that the ale keg had a slow leak in it.
I'm also tempted to brew a double-batch lager, keg them both and leave one keg in the fridge and one in high heat for a few months as I really did enjoy that lager!.
Is that info confusing enough for you Hoover?
PP
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