If beer is left exposed to the sun too long the UV rays break down the Alpha Acids in the hops and these then react with the sulfur in the beer and it actually forms a chemical that is almost identical to a Skunks' spray. I really dislike flavor and will go to great lengths (such as wrapping my beer in paper) to hide my beer from the sun when I'm drinking outside. Yup, I'm pretty embarrassing to hang out with... In fact, one of the projects I have been working on is an outdoor beer/camping mug that will protect beer from UV rays while still showcasing flavors (more on this some other time).
This is why MOST beer bottles are now brown. Brewer's figured out that by tinting/changing the color of the glass they could protect the beer from those UV rays. But wait, why do we have clear and green beer bottles? This is were the story gets interesting.
After World War II there was a shortage of brown glass, so breweries for the most part switched to clear bottles. In an effort to appear as a premium product and differentiate themselves from all the clear bottles, some European breweries opted for green glass instead of clear.
To this day, the choice to use clear or green bottles is a marketing decision more than a practical one. In fact, many breweries go to great lengths to keep their marketing position. They'll actually coat the glass to block UV rays. This maintains the flavor AND their marketing position (think Corona or Heineken). Pretty crazy right? If it wasn't for the shortage, all our beers would likely come in brown bottles instead of different color glass.
I still swear I can taste/smell skunked beer in most green bottled beers though.
3 Key Take aways:
- No, beer is not ever supposed to have the skunky aroma or flavors. It's an off flavor created by the hops in the beer being exposed to UV rays.
- It can be prevented, do not put your beer in sunlight... With some beers I can detect the off flavor after just seconds of exposure. High Alpha Acid hops are the worst offenders.
- Probably don't share this post with your friends who like those skunky beers. They may not appreciate the flavors as much once they learn they are actually drinking the same chemical that makes skunk spray.