The Angel's Share
The Angel’s take their share from every cask. In the simplest of terms, the Angel’s Share is the amount of spirit lost to evaporation as a whiskey ages. The amount the Angel’s take each year varies widely based on barrel size, time, environmental conditions and even the location of the warehouse. We ensure that our customers casks are stored within the best possible climate controlled locations.
A whisky barrel could lose 30% to 40% of its volume between the original barrelling and the time the liquid is ready for bottling, depending on when it is bottled.
This explains why a significantly aged Scotch Whisky which is bottled, is much more expensive to purchase.
Put simply, after the angels take their share, there isn't a lot left to bottle.