3

Very little information can be found around internet about "photoisomerization" in beers. This is a chemical reaction on acids of hops if exposed to the light, such as in transparent bottles.

I could find that the visible light of blue frequency only, and the invisible light UV (only), can cause photoisomerization, but it isn't widely known neither are consensus about that.

Someone could confirm that ? Or give more detailed information about the light frequencies that can cause photoisomerization ?

Assuming that just UV + blue light can cause it, I have a lot of questions like:

  • Why UV and blue light filters aren't used to non-brown bottles keeping the beer protected against the photoisomerization ? Just costs ?
  • What are in brown bottles that can filter UV ? What is their efficiency to filter UV and blue light ?
2

This Wired article may help shed some light on wavelengths and bottle colour.

http://www.wired.com/2013/03/physics-and-green-beer-bottles/

Amendment 1
Light in wavelengths of 350 nm to 520 nm (upper UV to mid-visible light) is known to cause skunky beer.

Green bottles allow green light (520 nm to 550 nm) to pass through, whereas brown bottles (ranging between 580 nm and 700 nm) block wavelengths known to skunk beer.

Iron and other metal oxides impart the brown tint.

Amendment 2
Incidentally, I just read that the "thiol" (organic compound containing sulfur) responsible for imparting the "skunk" is 3-methylbut-2-ene-1-thiol, a.k.a. "skunky" thiol.

Source: Chemistry - A European Journal, v7 n21 (November 5, 2001): 4553-4561

  • This is best left as a comment not an answer. – brewchez Oct 14 '14 at 12:53
  • Post amended to include an answer. – SynapticHammer Oct 19 '14 at 2:52

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