The content of alcohol in wine refers to the proportion of ethanol; the main type of alcohol present. The theoretically achievable alcohol content of a wine can be calculated by the must weight already in the grapes. It results from the sugar (fructose and glucose) in the must, which is converted into alcohol and carbon dioxide during fermentation. In the 19th century, the French chemist Joseph Gay-Lussac (1778-1850) developed a system that represents the alcohol content in degrees (°), which is still partly used in Anglo-American countries. Today, however, it is internationally accepted and standardised within the EU that the alcohol content is given in percent by volume. The measurement is made at a temperature of 20 °Celsius.