Your evaluation of newly purchased beer starts with the removal of the bottle cap. Did the bottle give a quick, healthy hiss? Did it gush like Mt. Vesuvius or fail to release any carbonation at all? Unless the bottle was allowed to get very warm or you did the hokey-pokey with it just before opening, a gusher indicates a potential wild fermentation in the bottle — not a good thing, but not anything that’ll kill you, either.
If a quick sniff doesn’t verify this possibility, a follow-up taste will. Vinegary tastes and aromas are usually good indications of a fermentation gone wild, but proper pasteurization makes this occurrence infrequent. And keep in mind that certain beer styles are meant to have a sour taste, and some are just naturally more highly carbonated than others. Don’t be too quick to judge.
If you didn’t get the usual fizzzt from the bottle, either the beer was improperly carbonated at the brewery (very unlikely) or the cap’s seal had a leak that allowed the carbonation to escape. These types of problems are virtually unheard of in well-known, brand-name beers and are usually limited to products from small, technologically challenged breweries.
Any beer that’s been laying around too long, regardless of whether it was pasteurized, reaches a point when it goes stale (becomes oxidized). The result is a beer that smells and tastes papery in the early stages and cardboardy in the advanced stages. Refrigerated beer is far less likely to become oxidized, but it can still happen over time.
Because the only ways to detect oxidation in beer are by smelling it and tasting it, you’re not likely to discover this flaw until you’ve already purchased the beer. This is another good reason to check freshness dates on the label or packaging before you buy.
