- UV light exposure causes negative effects (only a real problem for bottled beer).
UV light has a photochemical impact on hops. This causes it to have a flavor and aroma of a skunk. Brown bottles help lower the amount of UV light that can get to the beer, and with cans this is a non-issue.
- Extreme fluctuations in temperature are generally not good for the beer.
Extreme temperature fluctuations could impact the flavor of any drink, but most likely will be too subtle to notice.
- Bottled beers can sometimes re-ferment at higher temperatures, causing over-carbonation.
Yeast needs sugars to ferment, by the time the bottle is on the shelves, the fermentable sugars are completely fermented and the yeast is in a dormant stage. However, this doesn't mean yeast cannot still affect the flavor of the beer. If the beer is bottle conditioned, then it still has live yeast cultures and extra care should be taken to keep it below high temperatures (80+ F.) for long periods of time. You should not be concerned of it exploding (over carbonating), that only happens in homebrews where they added too much sugars or didn't sanitize everything properly.
The majority of commercial beers are filtered to such a high degree that there is little to no live yeast to be concerned about. Some beers are even pasteurized to kill any remaining yeast, removing the possibility of it affecting flavor and extending its shelf life.
Bottom line is, avoid temperature fluctuations as much as you can, but its not something you should throw away perfectly good beer for. If you are a supertaster that can detect the subtle flavor changes, give it away to one of the 75% of us who are not.
For a full scientific study with facts and figures way over my head you can see: Stability profile of flavour-active ester compounds in
ale and lager beer during storage