Why beer comes in brown bottles

I received a great book, “What Einstein Told His Cook 2”, for Christmas. (I’d previously read, and enjoyed, the first book.) This is a book about food and cooking, written by a chemistry professor. I hardly need say more about why it’s an engaging read, but I will anyway. I would much rather approach cooking from the science side, where there are rules and reasons and determinism, than from the art side, where there is chaos and personal taste and approximation. These books explain the whys and hows behind common kitchen practices, very sensibly, very educationally.

Therefore, I ended up finding the section on alcohol and various drinks to be enthralling, even though I don’t drink and expected it to be pretty much irrelevant. One tidbit I took away from the chapter was an explanation for why beer always comes in (opaque) cans or dark brown bottles:

Hops are an essential ingredient in beer, and not only for the aroma and bitterness. They clarify the beer by precipitating the proteins in the wort, and they have antibiotic properties that help preserve the beer. Among the more than 150 chemical compounds that have been identified in their essential oil are chemicals (terpenes) called isohumulomes, which are light-sensitive. When struck by either visible or ultra-violet light, they break down into very active free radicals that react with sulfur in beer’s proteins to produce smelly compounds called skunky thiols, which the human senses of taste and smell are able to detect at levels of a few parts per trillion. […] Beer that has been exposed to light for as little as 20 minutes reputedly can develop a “skunky” taste. That’s why beer is packaged either in cans or in light-proof brown bottles.

It had never occurred to me to wonder why beer doesn’t come in clear plastic or glass bottles, like soda. Now I know!