WHISKY EVAPORATION

One of the key factors that contribute to the unique taste of whisky is the maturation process, which involves aging the spirit in wooden barrels for several years. During this time, the whisky undergoes a series of chemical reactions that result in the development of its characteristic flavor profile. Evaporation, in particular, plays a vital role in this process.

The literal meaning of evaporation is the loss of alcohol, water, and other compounds from the cask in vapor form, leading to a decrease in the level of liquid in the cask. Despite the loss, evaporation is essential in the maturation of whisky. The process of evaporation reduces the level of sulphur compounds, which are created alongside a broad range of compounds during fermentation. These compounds can have rubbery, meaty, vegetal, and sweaty notes, masking other subtler characteristics like fruit notes and sweetness. By reducing the level of sulphur compounds, evaporation reveals these notes and significantly changes the flavor profile of the whisky.

The rate of evaporation is influenced by temperature and humidity levels. Warmer, drier conditions promote higher proportions of water evaporation, resulting in an increase in alcoholic strength. Conversely, cooler, more humid environments prompt the evaporation of more alcohol than water, reducing alcoholic strength. In Scotland, for example, the alcoholic strength of whisky decreases by about 0.5 percent ABV per year. The rate of evaporation slows with longer aging, but even in mild climates like Scotland, significant losses occur. The Balvenie Cask 191, for example, lost about 77% of its contents through evaporation between 1952 and 2002.

Evaporation rates can also be divided into the proportions of alcohol and water involved. Hotter, drier conditions promote higher proportions of water than alcohol evaporating, increasing the alcoholic strength. A cooler, more humid environment prompts the evaporation of more alcohol than water, reducing the alcoholic strength. The evaporation of alcohol and water at different rates also affects the texture of the whisky. As alcohol evaporates more quickly than water, it leaves behind more concentrated flavors and a thicker, more viscous texture.

The impact of evaporation is not limited to the flavor and texture of the whisky. It also affects the volume and yield of the final product. The rate of evaporation is not uniform, with different climates experiencing varying rates. In Scotland, the temperate climate results in average annual evaporation rates of around 2 percent of the contents of the cask, while in Kentucky, it's 3-5 percent. The Australian climate varies significantly, with the evaporation rate in Tasmania around 3 percent and in Melbourne 5 percent. In Israel, evaporation can reach 10 percent, and in India up to 12 percent. The loss of volume due to evaporation results in a smaller yield of whisky, making each drop even more precious.

Source: The Whisky Dictionary: an A-Z of Whisky, from history & heritage to-distilling & drinking