BEER CHEMISTRY

Are brown bottles better for beer?


Beer is typically made from water, malted grains, yeast and hops, which combined to produce more than 600 volatile compounds. These chemical reactions continue to occur as the beer ages. And as with most chemical reactions, they are affected by energy in the forms of both heat and light. Some of these reactions can yield a mellower flavor. Too much light, however, can be a problem and leads to ‘lightstruck’ or ‘skunky’ beer.

The substances that are most affected by light are found in hops. Hops are the cone like flowers of the climbing plant Humulus lupulus and are used to give beer its bitter flavor and many unique aromas. When light reacts with certain hop-derived compounds, it creates a variety of unpleasant-smelling and -tasting chemicals, with 3-methyl-2-butene-1-thiol (MBT) being the major offender.

Light-resistant hop extracts are now available that can help prevent beer from becoming lightstruck. Antioxidants can also be used. But these approaches affect the final taste of the beer. The best solution is to keep the beer from being exposed to light. And that is achieved through the packaging. Cans are optimal, but for glass bottles, brown glass blocks out more light than green glass, and both are far better than clear glass. Dark beers, which absorb more light, are best bottled in brown glass, while green glass is generally fine for lighter beers.