Every distiller knows the phrase. Few can tell you, on any given day, what the angel's share is costing them this quarter. It gets treated as folklore, and then it shows up as a surprise when the barrels come down lighter than the spreadsheet assumed.
It does not have to be a surprise. Evaporative loss is measurable, it follows patterns, and once you track it at the barrel level it becomes something you can forecast and price around.
It is not one number
The headline figure, often quoted as a few percent of volume per year, hides most of what matters. Loss varies by:
- Location in the rickhouse. Upper floors run hotter and lose more, often dramatically more, than the ground floor. Two barrels filled the same day from the same batch can diverge by the time they are dumped.
- Season and climate. Hot, dry stretches pull volume and push proof up; humid stretches behave differently. A single annual percentage smooths away the swings you actually plan against.
- Barrel age and entry proof. The curve is not linear across a long maturation.
Average it all into one rate and you lose the ability to explain, or anticipate, what any specific barrel will yield.
Why it belongs on the books, not in legend
Angel's share is a real cost. The spirit that evaporates was made from grain you bought, distilled with energy you paid for, and stored in a barrel that is itself an asset. When a barrel yields fewer proof gallons than planned, your true cost per proof gallon on what remains goes up.
If that is not flowing into your costing, then your cost per barrel, your margin by release, and your pricing are all working from a volume that no longer exists. The number you sell against is fiction by exactly the amount the angels took.
Turning it into a forecast
The path from folklore to forecast is straightforward in principle:
- Gauge and record proof and volume at fill, at any interim regauge, and at dump, for each barrel.
- Attribute loss to position, age, and season so the pattern is visible rather than averaged away.
- Project forward from those patterns to estimate what barrels still aging will yield, and when.
- Feed it into costing so cost per remaining proof gallon, and therefore margin, reflects reality.
Do that and the angel's share stops being a year-end write-down you explain after the fact. It becomes a line you forecast, a loss you can locate to a floor and a season, and an input to how you price every release.
Spirit Sight tracks proof and volume at the barrel level through the full maturation, models loss against position and time, and carries the result into barrel valuation and costing, so the number you plan against is the number that is actually in the rickhouse.