Google search "Beer and Sunlight"
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Enemy #1 – Sunlight!
Beer has several natural enemies. The first is light, especially direct sunlight. Nothing will get a beer to go bad faster than days of direct sunlight. This is reason that most beer bottles are dark brown color. Although the clear Corona bottles show off the beautiful yellow color of the beer, the bright Mexican sunlight can get in and turn the beer against you.
The hops flowers used to give beer its flavor are extremely sensitive to the ultra-violet radiation streaming from the Sun. Even if exposed to sunlight for less than an hour, beer will undergo a chemical reaction that creates an organic compound called 3-methyl crotyl mercaptan. Give that a sip, and you’ll understand why a beer can be called “skunky”.
Most supermarkets use display cases lit by fluorescent light. They’re bright, and cheap to operate, but they blast out the ultraviolet radiation that can set a beer going skunky. If you want to best beer you can buy, look for bottles kept in a dark box, away from the sunlight and fluorescent lights. Cans are safe too.
Brewers can battle this process by using hydrogenated hop extracts instead of fresh hops, but then you’re not getting the best quality beer.