One of the terms often used in distilleries is “the angels’ share”. When spirits such as whisky are slowly maturing in their casks, a small amount of spirit evaporates through the wood and into the atmosphere. Roughly 2% of each cask evaporates per year, so it was playfully labelled as a sacrifice to the heavens. By giving the angels their share, Distillers ensure their drams are the best they can possibly be when it’s eventually bottled. Why this happens and what we can do about it is just one of the more complex jobs for our Master Distiller to contend with.
There are several factors affecting how much of the spirit is lost to the heavens. These include:
THE AGE OF THE SPIRIT
Spirits tend to evaporate more quickly while they’re young, and then slow down as they age. When spirit casks are first filled, the angels’ share is higher – around 3.5% to 4% every year. As the liquid ages, it continues to evaporate (it will never stop), but it will do so at much lower rates. By the end of its maturation period, a 20-year-old spirit might lose 40% of its volume.
THE SIZE OF THE CASK
The size of the casks impacts the amount of spirit that is lost. For example, whiskies stored in smaller casks will evaporate more, because they have more liquid-to-wood contact. Casks that hold less than 50 litres can lose a significant portion of their original fill volume. However, this leads to a faster maturation.
THE CLIMATE IT’S KEPT IN
The climate has a significant impact on evaporation. The bourbon warehouses in Kentucky may experience 50- 60 degrees heat on the top floor of the warehouse while the bottom floors may only experience 20-degree heat. The heat impacts the speed of maturation and evaporation; the casks on the warmer floors will lose liquid faster. The humidity also effects the way the liquid evaporates. As Kentucky is a humid climate, water leaves the cask first (rather than alcohol), strengthening the spirit. This creates a big contrast between the hot humidity of Kentucky and the Oceanside Speyside climate, where the alcohol not the water leaves the spirit first.
THE WAY IT’S STORED
Airflow also has an impact on the spirit. In bigger warehouses, casks are often stored on racks or pallets, which means they’re raised slightly from the ground. Air circulates around them, leading to greater evaporation.
These are just some of the factors that can affect the angels’ share. These conditions are consistently assessed by the Master Distiller’s and other experts in order to produce the best possible drams.