Preserving Beer Freshness
You may have heard the term “skunky brew.” Turns out that’s an accurate label for what happens to beer when it’s exposed to light. Hops contain bitter molecules called isohumulones, and any type of light—whether natural or artificial—causes these molecules to produce free radicals. In turn, the free radicals react with a sulfur compound in beer to produce a compound called MBT, which is a component of skunk spray. It takes very little MBT to produce a skunky off-flavor in beer: Some astute tasters have detected as little as one-billionth of a gram per 12 ounces of beer.
To evaluate the damaging effect of light, we poured beer from its protective amber bottle into a clear pint glass and placed it on a sunny windowsill. We opened two more bottles from the same six-pack, wrapping one in aluminum foil to keep as much light blocked out as possible, and placed both on the same sill. After 30 minutes, we sipped all three brews and immediately noticed a difference in the beer exposed to sunlight, which developed pronounced off-aromas and—flavors. The beer in the wrapped as well as unwrapped amber bottles tasted just fine. We repeated this test under fluorescent lighting and got similar results.
Hopefully, your favorite beer comes in cans or amber bottles. At the very least, avoid clear or glass-bottle six-packs that have been sitting in the front of a store shelf or at the top of a commercial refrigerator near fluorescent lighting. For the best-tasting beer from start to finish, use a beer cozy to keep your brew cold and to block as much light as possible from the bottle, colored or clear.