So far in our exploration of beer off flavors, we’ve covered diacetyl (butter) and acetaldehyde (apples). While common, you may not have experienced those off flavors yet. But I bet you’ve had skunky beer. It’s probably the most common off flavor out there and you can usually smell it better than you can taste it. It’s a strong skunky aroma, some would call it musky.
Skunky beer is also called “light-struck” because light is the culprit here, specifically ultraviolet (UV) light. Ultraviolet light breaks down the hops’ isomerized alpha acids which reacts with hydrogen sulfide (from the yeast) to make mercaptan. Mercaptan is also a component of skunk spray. It surprisingly takes very little UV light to induce skunkiness. And while some off flavors are acceptable in some style of beer, like diacetyl in some British ales, skunked beer is never appropriate.
Light-struck beer can easily be prevented with proper packaging. Brown glass keeps 98% of the offending UV out of your beer. This is an area where cans are superior to bottles, they block 100%. Green glass only blocks 20% of the UV, letting in a whopping 80% to skunk your beer. Green bottles are not your beer’s friend! Props to Pilsner Urquel who has started shipping their bottles in cardboard packaging that completely blocks light. Clear glass does not block UV! Remember that the next time you have a Corona; it’s not Mexico your tasting, it’s skunk. Add a lime, indeed. Speaking of clear glass, don’t forget growlers. Many breweries and growler shops sell brown growlers, but clear growlers still hang around. Do yourself a favor and get one of the new stainless steel growlers, they block all light.
Almost every rule has an exception. Miller ships High Life, Genuine Draft & 64 in clear bottles yet those beers do not get light-struck. Magic? No, science. Miller uses a special hop extract that does not react to UV light. Still, there are plenty of other reasons why High Life tastes bad.
Your beer can skunk anywhere it’s exposed to light, like the cooler at your local grocery. Seriously. If it sits in a bright cooler long enough the UV glow of the fluorescent light can skunk the beer. Even worse, it can happen while you’re drinking a pint on your favorite patio. It doesn’t take long for a beer sitting in direct sunlight to get skunky.
There a misconception going around that letting cold beer get warm causes skunkiness. A customer at the bottle shop where I work asked for a warm 6-pack because she didn’t want the cold one the warm up before she got it home. I asked why, and she said because it would get skunky. No it won’t. Don’t let cold beer warm up, but if it happens once, it’ll be OK. Just don’t cycle it from cold to warm to cold many times. That will eventually hurt your beer. That’s another conversation about keeping beer that we’ll get into later.
Here’s to perfect beer! Cheers!