The Cognac is progressively reduced to 40% abv. by adding pure, distilled, or demineralised water
When Cognac is released to market, its minimum alcohol content is 40% abv.
During ageing, evaporation contributes to the progressive reduction of the alcohol level. It varies with storage conditions, but averages 2% per year.
In general, however, this natural loss of alcohol is not sufficient. Pure, distilled, or demineralised water must be added to the eau-de-vie. This operation, called “reduction”, must be progressive and executed in several stages.
Alcohol content influences the ageing process. Therefore, some people prefer eaux-de-vie “reduced” early and then aged.
Reduction is not a specific requirement mandated by the AOC. It is possible to find very old eaux-de-vie that have been reduced solely by natural evaporation.