Pic(k) of the Week: Beware the mercaptans!

Alfresco may be beautiful but beware the mercaptans. Beer lovers don't allow their beers to get 'skunked.'

About beer, hops, sunlight, and mercaptans (aka thiols):

Certain compounds in hops are light-sensitive and when exposed to strong light a photo-oxidation reaction takes place, creating the intensely flavor-active compound 3-methyl-2-butene-1-thiol (MBT), one of the most powerful flavor substances known to man. Commonly referred to as 'skunky,' the pungent odor resembles that of the famously malodorous defense spray deployed by skunks.

— The Oxford Companion to Beer: Oxford University Press, 2012.

To ward off the stank, keep beer out of direct sunlight or fluorescent light. Cans (and kegs) are best for that and brown glass is ok. But green glass? In sunlight, it's nearly worthless (e.g., that 'Dutch' beer) and clear glass (or plastic) is merely a vessel for liquid skunk (e.g., almost every 'craft' beer patio). Yummy...not.

Light-struck vs. oxidized

PS. Light-struck 'skunkiness' is NOT the same off-flavor (or biochemical mechanism) as that in a beer left warm. Beer exposed to heat (and over time, such as an old beer) will oxidize. The beer will develop malodors such as cardboard (!) and sherry and quickly lose its hop aroma. This can happen to any beer left warm, whether in direct sunlight or not, whether in a can, in brown glass, or in a keg.

By the way, when a beer is pasteurized, it is deliberately exposed to high heat over a short period of time. Draw your own conclusion.

A series of occasional reviews of beer (and wine and spirits).
No scores; only descriptions.

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• The beer sacrificed in the sun? A draught-pour of Night on Ponce, an IPA (7.5% alcohol) brewed by Three Taverns Brewery of Decatur, Georgia. The photo shoot at a local pub took only a moment; the beer was quickly rescued, removed to a darker table.


• Pic(k) of the Week: one in a weekly series of images posted on Saturdays, occasionally, as is the case today, with a good fermentable as the subject.
• Photo 13 of 52, for year 2021. See it on Flickr: here.
• Camera: Olympus OM-D E-M10 II.
  • Lens: Lumix G 20/F1.7 II.
  • Settings: 20 mm | 1/640 | ISO 200 | f/2.8
• Commercial reproduction requires explicit permission, as per Creative Commons.


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