Not the green bolttes but UV light.
Brown bottles do the best at filtering out the uv light. Heineken beer was once known for this defect and built its world reputation on peoples' ignorance of it. Many people thought the "skunkiness" as normal and a quality beer aroma and flavor. This actually is not too far from the truth as some hops do have a special aroma that is similar to this skunk aroma.
The longer time a bottled beer is exposed to uv light the greater the sunstruck charater of the beer. This is true for brown, green, or clear bottles.
Heat does not cause this skunk defect in beer.
Light Struck MBAA
When beer, particularly lager beer, is exposed to sunlight in clear bottles it developes an unpleasant 'sun-struck' flavor due to the formation of isopentenyl mercaptan. It is envisaged that photolysis of isohumulone cleaves the isohexenoyl side-chain to form a 3-methylbut-2-enyl radical which reacts with hydrogen sulphide, or any available thiol, in the beer to produce the mercaptan stated above.
Malting and Brewing Science, Volume 2
J.S. Hough, D. E. Briggs, R. Stevens and T.
So, a cyclic isohumulone (the alpha acid of hops) compound is broken with uv light and a sulfur (likely Dimethyl sulphide derived from barley malt or corn grits) attches to it. The result is the
3-methylbut-2-enyl thiol (prenyl mercaptan) which produces the sun-struck "skunkiness" noticed in poorly handled beer. Heineken has this problem.
NOTE: I wrote Miller to ask them how they achieved these great results. Here is their response:
We currently only use hops grown in the United States. The major growing areas are in Oregon, Washington, and Idaho. Some of the types of hops we use include: Cascade, Cluster, Fuggles, Galena and Mt.Hood. Unfortunately, because it is proprietary information, we cannot disclose which hops are used in which brands.
In addition bottled beer exposed to sun or other light sources can undergo a slight photochemical change that sometimes can give the beer a skunky aroma, however, the beer would not get skunky. It would take approximately one minute for this change to take place. Cans provide the most protection from light, and generally product in amber bottles is LESS likely to suffer the effects of light than beer packaged in clear or green bottles. The exceptions are all Miller products that are sold in clear bottles. Miller's understanding and use of special hops enables us to produce a beer that is much more light stable. However, other subtle flavor changes can occur with exposure to too much light. So, keeping any bottled beer (clear or amber) out of direct sunlight helps preserve that just brewed flavor of our products.
Beer is most susceptible to light exposure in the 290 - 425 nanometer range. Amber glass does an excellent job of preventing light from reacting with product in this range.
· 1 decade ago