The alcohol content of wine and other alcoholic beverages refers to the proportion of ethanol, the main type of alcohol present. The theoretically achievable alcohol content of a wine can already be calculated from the must weight in the grapes. It results from the sugar content(fructose and glucose) in the grape must, which is converted into alcohol and carbon dioxide during fermentation. In the 19th century, the chemist Joseph Gay-Lussac (1778-1850) developed a system that expresses the alcohol content in degrees (°), which is still used in some Anglo-American countries. Today, however, it is internationally common and standardised within the EU to express alcohol content in percent by volume. The measurement is made at a temperature of 20 °Celsius.
Definition of terms
There are four different terms for alcohol content. The main interest is in how much alcohol is actually contained in the drink. In most countries, the actual alcohol content is stated on the label:
actual alcohol content
Pure alcohol actually contained in grape must or wine.
Potential alcohol content
The amount of alcohol that would theoretically still be possible if the residual sugar were fully fermented (potential = possible, as opposed to actual). In Italy, this value is often given after the existing alcohol content in the form of "14% vol+4", for example. In this specific case, this means a residual sugar of the equivalent of 4% alcohol, i.e. around 65 g (1% alcohol corresponds to 16 to 17 g sugar).
Total alcohol content
Sum of actual and potential alcohol content.
Natural alcohol content
Total alcohol content before any fortification.
Calculation
During fermentation, 10 g of sugar per 1,000 g of must produces 0.66% alcohol by volume. A content of 8 g alcohol per litre corresponds to around 1° or 1% vol. The conversion formula is % vol x 7.894 = grams of alcohol per litre (g/l) of wine. At 12% vol, this results in 94.7 g/litre. In a 0.75 litre bottle of wine, this is 71 g of pure alcohol. An eighth of wine contains approximately the same amount...
