Beer has an unusual sensitivity to light. Even brief exposure to light under the wrong conditions can alter the aroma and flavour of beer, giving it a distinctly unpleasant character. The result is known as lightstruck or ‘skunked’ beer- because it smells like the common American skunk!
Skunking occurs when beer is exposed to specific wavelengths of light, which are found in fluorescent light and sunlight.
Beer packaging can protect beer from light. Kegs, cans and cardboard case boxes- all keep light from reaching the beer inside and therefore prevent skunking or a lightstruck flavour.