I often come across guides on detecting off-flavors. But I never seen a guide on how to how to identify flavor caused by poorly aged beer, though I’ve come across plenty of home brews past it’s prime. Is there a general rule on flavors appearing late? Certain off-flavors to be on the lookout for? It’s definately the case that home brews in most cases age worse than pasteurized store-bought beer, in my experience (especially for low gravity beers).
It's not only homebrew! I needed some swing top bottles, and obtained a crate of empty bottles from the liquor store. But part of them was not empty.
Those were Floreffe Tripel bottles, still sealed, but the expiration date was March 2018. Not too far out one would say, but what I smelled and tasted reminded me more of port wine. But a little bit too funky to be nice.
All beer changes with age.
Delicate intangibles of hops and malts are first to fade away. Many styles are best fresh. Kolsch, Pils and anything hop forward.
What happens in aging is these flavors and aromas fade and meld into the whole of the beer. Not always a bad thing.
As far as worse case for homebrew. It would be infections or brewing defects that become more apparent with age because as fresh thier flavors were masked. Diacetyl, DMS being the most common. Acetobacter is worse case turning a beer to vinegar.
Mishandling, poor bottling and storage are other issues that will creep up with age. Oxydation, light struck.
Warm storage will accelerate almost all of the issues.
Aging can help many styles and brewing defects. Fusel alcohols, overly bitter from hops and wood, funks from bacterial fermentations (sours, bretts), astringency from wood (not tannins). All of these will change and usually reduce with age.