Subject: 520 nm
Date: 1991-11-07 07:03:05 GMT
Volume 8, Number 2 of New Brewer (March-April 1991) mentions the
magic number on page 10 in an article by Owens-Brockway entitled
"The Right Glass":
"The degeneration problem occurs most frequently in warehouses or
retail outlets where fluorescent lighting is the norm. While all
light with the wavelength of 520 millimicrons has the potential to
cause beer skunkiness, it is the ultra-violet (UV) portion of the
light spectrum below 400 millimicrons that is the most harmful to
beer in the shortest period of time. (See graph.) In fact, it can
affect beer flavor in as little as 24 hours."
The graph, which I obviously cannot reproduce, shows that amber
glass transmits about 5% of the light below 400 nm (UV), green
glass about 80%, and clear glass about 90%. Between 400 and 520 nm
(green), amber glass climbs from 5% to 30%, green drops from 80% to
50% (at 450 nm, which is blue-green) and then climbs back to 80%, and
clear glass stays around 90%.
If these facts are correct, the correct technical choice for bottle
color cannot be controversial.
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