alcoholic strength, an important measurement of any wine, is its concentration of the intoxicant ethyl alcohol, or ethanol. It can be measured in several different ways, the most common being the degree first defined in France by Gay-Lussac in 1884. This was the number of litres of pure ethanol in 100 litres of wine, both measured at 15 °C/59 °F. Later a more precise definition, using 20 °C/68 °F as the reference temperature and some other minor refinements, was adopted in France and by most international organizations. The degree of alcohol is equivalent to its percentage by volume and is sometimes referred to as ‘abv’, alcohol by volume. In most countries it is mandatory to specify the alcoholic strength of all wines on the label, although it may be written either % or occasionally ° (see also labelling information).