Angel’s Share is a term I love to share with both my wine geek friends and those who have no clue about wines whatsoever! It’s a good descriptive term indeed!
As a wine ages in barrel, water and/or alcohol is lost due to evaporation. What exactly is lost varies from barrel to barrel and site to site, depending upon the relative humidity and temperature of the wines during storage and how consistent these paratmeters remain. This ‘loss’ is known as the Angel’s Share because it is not ‘captured’ by any vessel – just lost ‘into the air’ . . .
The ‘ideal’ humidity level for long term barrel storage is about 70%. If the humidity level drops lower, then you end up evaporating more water out of your barrel then alcohol, thus slightly increasing the alcohol level of the wine that remains. If the humidity level is higher, you end up evaporating more alcohol from the barrel, thus slightly decreasing the alcohol level of the wine that remains.
The important thing from a winemaker’s perspective is that you will lose quite a bit of wine due to this process each year – up to 5 gallons per barrel! It is therefore imperative to keep on top of this and make sure your barrels are ‘topped’ on a regular basis . . . and that Sulfur Dioxide is added to ensure that the wine is in an anti-oxidative state.
Let me know if you have any questions about this term or any others! Cheers!