Dark Beer VS Light Colored Beers

Are you saying dark beer in a clear bottle? If so, it will skunk in light just like a light colored beer in a clear bottle.

 

My guess is that it will skunk at a slower rate, but since the beer on the outside of the bottle is in contact with the light, it will still spoil eventually. Even beer in a brown bottle will skunk in direct light if given enough time.

 

Based off some green bottled dark European lagers I have had in the past I do not doubt that they can still skunk.

 

Many breweries use extracted hop oils to prevent skunking-the chemical that causes the skunk taste is removed during the extraction process. Miller uses this process so it can sell it's beer in clear bottles.

 

No offense to rocdoc1 but I wanted to clear this up. "The Chemical that causes the skunk taste..." is actually the hop oils themselves, and they are not "removed during the extraction process", they are simple isomerized (molecularly rearranged) so that if they're hit by UV light they don't isomerize into the usual arrangement that's similar to that of skunk juice.

 

Lightstruck flavor in beer
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by Martin Lersch / February 16th, 2007

Some years ago, a group of researches studied the formation of lightstruck flavor in beer (Chem. Eur. J. 2001, 4554). They found that isohumulones, compounds contributing to the bitter taste of beer, decomposed when exposed to ultraviolet light. In a recent blogpost, Harold McGee elaborates on this and it turns out that the way this happens is even more complex than first anticipated. The researchers (J. Agric. Food Chem, 2006, 6123) found that riboflavin (vitamin B2) acts as a photosensitizer in beer (and in olive oil, milk and butter) which catalyzes the conversion of oxgyen to a more reactive type of oxygen (singlet oxygen). This oxygen then “destroys” isohumulone and in the process radicals are formed.



As shown in the figure, the radical reacts with sulfur containing proteins, thereby forming a thiol called 3-methylbut-2-ene-1-thiol or just MBT for short. The amazing thing about this compound is that we can smell it at concentrations as low as a few parts per billion (ppb). The perhaps not-so-amazing thing is that this compound gives beer a “skunky” aroma. Obviously one would want to avoid this, and that’s why beer is sold in dark brown glass bottles that act as the beer’s own sunglasses. Canned beer of course will not go skunky (well not until it’s poured into a glass and served outside in bright sunlight – that will turn any beer skunky within minutes).