Alcohol levels in wine appear to be rising—but why, and should we be concerned?
The alcohol content of a bottle depends on the wine, the grape variety, decisions of the winemaker and, where appellation d’origine contrôlée regulations apply, the region.
The AOC laws decree that wines from Burgundy should be 13 per cent alcohol by volume so, in difficult years, winemakers may be forced to increase the level through “chaptalisation.” In the 19th century, Jean-Antoine Chaptal invented the technique of adding sugar to the fermenting juice for the yeast to convert to alcohol. There is no need to resort to such measures in hot years, but in that case the wines can have too little acidity. Winemakers may increase it by adding tartaric acid to the barrel. Thankfully, the rules state that no barrel can be both acidified and chaptalised (although nothing prevents the wines from different barrels being blended!)
By contrast, Bordeaux winemakers used to aim for 12.5 per cent in each bottle. These days, however, Bordeaux reds regularly reach 14 per cent, a figure that would once have been associated with the rich red wines of Amarone, where the grapes’ sugars are concentrated through sun drying.
What explains the rise in alcohol levels? Climate change? Perhaps, and long-term records of harvest dates provide some of the best evidence of shifting temperature patterns. But it is just as likely to be a result of technique and handling. As Benjamin Lewin, a scientist turned wine writer, has pointed out, the use of closed instead of open vats don’t allow so much alcohol to evaporate.
Grape variety is another key factor. The Riesling grape can produce wines with alcohol content as low as 10 per cent, which makes for an ideal lunch-time wine. The Gewürztraminer and Zinfandel grapes produce viscous, high alcohol wines, with some reaching a whacking 17 per cent. Viticulture matters here, too: late picked grapes will have higher sugar levels, leading to more alcohol, unless fermentation is curtailed to leave more residual sugar in these off-dry and sweet wines. Let the fermentation run and you will have high alcohol, glycerol wines, loved by many New World winemakers.
Against this trend there have been loud calls for lower alcohol wines. There are techniques, such as reverse osmosis, to reduce alcohol in the finished wine. But this is not part of traditional winemaking and is considered “cheating” by many producers.