Not all governments check the alcohol level of wine they import, but Ontario in Canada does and that is how academics from the American Association of Wine Economists were able to analyse data taken from 129,123 bottled samples from 1992 to 2009.
As part of its import controls, the Liquor Control Board of Ontario – which strictly controls sale of alcohol in the province – tested 80,421 reds and 46,985 whites over the 17-year period from all the major wine producing regions of the world, providing a cross-section of consumption. The academics excluded German wines, which typically have high residual sugar and sweet desert wines.
The difference between actual strength and what’s reported, % ABV. Download the data
Taken together and averaged, the results show that every country tends to understate the alcohol levels of the wines with Argentina, Chile and the United States tending to do so most and Portugal and New Zealand the least.
Overall, 57.1% of the samples understated alcohol content and the average alcohol content was 13.6% and the average reported alcohol content was 13.1%.
The Liquor Control Board of Ontario allows winemakers to err by one percentage point which is double the allowance in the UK for imported wines.
The problem of understating wine alcohol was worst in 1997 and 2003 and has happened progressively less between 2004 and 2007.
The background to the findings is the growing strength of wine and the data shows the average bottle strength rising from just above 12.6% in 1992 to just over 13.6% in 2006. The data showed that strength grew at different rates for different wine-producing countries with average alcohol rising by between 0.2 percentage points and two percentage points on a base of 12%-13%.
Taking heat data into account, the economists argued that he rise can only partly be ascribed to rising temperatures due to climate change. It would take a 6.7C rise in average temperature in the growing season to account for a one percentage point increase in alcohol, they said.
The data is below. What can you do with it?
Wine strength by country
Click heading to sort table. Download this – and more – data
All wine, strength
Reported % by vol
SOURCE: American Association of Wine Economists