Light Absorption by Various Beer Bottle Glass:
Data to Accompany April 2nd, 2008 Basic Brewing Radio Podcast with James Spencer.
Bradley E. Sturgeon, PhD
Department of Chemistry Chemistry
Monmouth, IL 61462
Light can alter the properties of beer through a general process referred to as photochemistry;
chemistry as a result of light (“photo”). The photochemistry details associated with “skunking”
of beer have been well investigated and the interested reader is referred to Burns, S.B. et al.
(Chem. Eur. J. 2001, 7(21), pages 4554-4561). To prevent photochemistry in a beer, beer is
generally packaged in brown bottles to prevent photochemistry from occurring. In this short
report, we will measure the light that is transmitted through different colors of beer bottle
packaging and conclude with some general recommendations.
Shown in Figure 1 (black line) is the emission spectrum (or light given off) from a
standard 40W tungsten light bulb (TLB). When this light shines on a bottle of beer, certain
wavelengths of light pass through the glass and can potentially alter the beer properties via
photochemistry. When beer stored in a clear glass bottle is exposed to light from a TLB, the light
is not shielded (the emission spectrum is unchanged – data not shown) and as a result, all
wavelengths (shown in black) will pass through the bottle and potentially alter the properties of
the beer. When beer stored in a brown bottle is exposed to the tungsten light, the majority of light
is absorbed (brown line), hence leading to a greater protection of the beer when compared to the
clear glass bottle. When beer stored in a green or blue bottle is exposed to tungsten light, some of
the light is absorbed (green – green line; blue – blue line), although the protection is not as great
as with the brown bottle. Table 1 presented at the end of this document shows the specific
absorption values and percentages at selected wavelengths.
Figure 1: Emission spectra from standard