Skunky Beers Aren't Brewed With Swamp Gas

By Chuck Sudo in Food on Dec 12, 2006 4:00PM

We came home from work Friday night with a simple plan: order in from Phil's Pizza, crack open a beer, and veg out watching some DVDs while the dog curled in front of the fireplace. And the plan was unfolding effortlessly. Phil's had the pizza delivered in under an hour, the fireplace was roaring so strong Emmy wasn't begging for pizza, Val Lewton's "Cat People" was queued in the DVD player.

And as soon as we closed the refrigerator door and cracked the top off the bottle, one whiff was all we needed to remind us why we don't drink Stella Artois, especially in bottle. The odor that emanated from the bottle was, to quote the security guard at the Jewel by our house, "stankin' something musty." In our hands was one of the skunkiest beers we've ever opened. If it smelled that foul, we weren't about to drink it, so we fed it to the kitchen sink.

To be fair, the bottles of Stella were leftovers from a movie night we hosted in our backyard a few months back. We had them in our pantry since that rainy August night, but it gets a lot of sunlight during the summer months, which sort of defeats the purpose of having a pantry, in the first place. We always wondered why beer - particularly beers in green or clear bottles - suffers from photo degradation, which causes skunk. It's an eternal question that, when we started research for this post, was answered five years ago by chemists at the University of North Carolina.

Using lasers as a light source and isohumulones (bitter acids derived from hops) supplied by breweries, the chemists placed beer in a process known as time-resolved electron paramagnetic resonance spectroscopy, in order to create photo degradation in the beer. They succeeded in creating a free radical that they named "skunky thiol", similar to what's found in skunk glands.

It turns out that hops, in addition to adding flavor to beer, retarding bacterial growth, and helping give a beer's head its stability, are also sensitive to light. When you leave a beer exposed to light, the hops break down to create the skunky thiol. The conventional - and scientifically proven - wisdom is that tinted glass helps reduce the process of photo degradation. Brewers love having this information because it's cheaper to bottle beer using clear glass bottles, and they want to turn a profit by any means necessary. SAB Miller has long added a chemically modified hop compound to their beers, which slows down the photo degradation process in beers like Miller High Life and MGD. Other breweries simply package their beers to where they're kept in the dark as long as possible.

Finally, it can explain why some beers taste better out of a can than from a bottle. Stella Artois, which is sold as a premium lager in the US and Great Britain, can be found in eight-ounce pony cans in its native Belgium. At least, it could twenty years ago when Slayer was pictured drinking it on the back cover to "Reign in Blood." If you're the type of beer drinker who's into cellaring or letting beers age, make sure you keep it in a cool, dark part of your pantry.