Definition: Gay-Lussac degree

The alcohol content is expressed in Gay-Lussac degrees, i.e. the volume of pure alcohol at 15°C per 100 volumes of distillate. (Generally speaking, the alcohol content of a traditional beer is expressed by a figure slightly lower than the figure representing the original wort's degree-régie. Example: a luxury beer with an original density of 5 degrees will have an alcohol content of around 4.5 degrees Gay-Lussac.) EU wine regulations use 20°C to carry out this measurement.