In short: The angel share is the spirit you lose to evaporation while barrels age, typically around 2 to 3 percent per year for a full 53 gallon barrel. That ordinary evaporative loss is generally not taxed, because the spirit is still sitting in your bonded storage account and has not been removed for sale or consumption. You still have to gauge it, record it on your storage report, and be ready to show TTB the loss is real. Federal excise tax attaches when you remove the spirit from bond, on the proof gallons you actually take out.
One question comes up on the ADI forums again and again, usually phrased almost exactly this way: "How would I account for the 20% loss? I didn't destroy it and I didn't take it out of inventory." It is a fair question, and the confusion is understandable. You filled a barrel with a known quantity of spirit, the angels drank some of it, and now you have to reconcile a number that shrank without you doing anything. This post walks through what the angel share actually is, how much of it to expect, how to record it, and the part that trips up the most distillers: when a storage loss is taxed and when it is not.
What is the angel share and how much should I expect to lose?
The angel share is the portion of aging spirit that evaporates through the wood of the barrel over time. It is not a defect and it is not avoidable. Oak breathes, and a charred oak barrel sitting in a warehouse for years will give back a meaningful fraction of what you put into it.
For a standard 53 gallon barrel, distillers on the forums consistently report ordinary losses in the range of 2 to 3 percent per year, climbing as high as roughly 10 percent per year in hot, dry climates. Those are real-world numbers from people storing real inventory, not marketing figures, and your own warehouse will land somewhere on that curve depending on climate, warehouse position, and how tight your barrels are.
Small barrels are a different animal. Because evaporation is driven by the ratio of barrel surface area to liquid volume, a small barrel loses far more, far faster. Distillers have reported five gallon barrels losing 8 to 10 percent in just six months, which is several times the annual rate of a full-size barrel. If you are aging in small cooperage, plan your fill quantities and your timeline around that, because the loss will eat into your yield quickly.
A few other factors push the number around. Vertical, palletized storage tends to lose slightly more than horizontal storage because of hydrostatic pressure on the lower staves, though many distillers accept that trade for the handling speed. Stacking barrels four or more levels high stresses the staves on the bottom barrels and can increase evaporation. Dry, high-altitude conditions accelerate loss and loosen seals, which is why some distillers periodically hose down the outside of their barrels to keep the wood swelled and the seams tight.
Why does barrel proof rise in one warehouse and fall in another?
This surprises new distillers, but it is one of the more useful things to understand about aging. When you lose volume to the angel share, the proof of the remaining liquid does not stay fixed. It moves, and the direction depends on humidity.
In a drier environment, water passes through the staves faster than alcohol, so the spirit that remains in the barrel gets stronger and the proof rises. In a humid environment, alcohol leaves faster than water, so the proof drops. The barrel loses total volume in both cases, but whether you end up with a higher-proof or lower-proof spirit at dump is a function of where the warehouse sits and what the air is doing.
This matters for your loss math because of how the regulations treat the two measurements. You barrel at a known proof. The quarterly loss you report is based on the change in wine gallons, computed at that original barreling proof, not on a fresh proof reading every quarter. You do not reproof every barrel every quarter, which would be impractical. You reproof and record any additional loss when the spirit actually leaves your storage account.
Is the angel share taxed?
For most ordinary evaporation, no. This is the part worth being precise about, because guessing wrong in either direction costs you money or invites trouble.
Federal excise tax on distilled spirits does not attach at the moment of distillation, and it does not attach while the spirit sits aging in your bonded premises. It attaches at removal from bond for consumption or sale. That is the whole point of a Distilled Spirits Plant operating under bond: you can hold and age inventory without the tax coming due until you actually move the spirit out into commerce. The federal tax framework and the rates are documented by TTB at ttb.gov, and the underlying statute on attachment and determination of tax sits in 26 U.S.C. Chapter 51.
So when the angels take their share out of a barrel that is still sitting in your storage account, that spirit was never removed for sale and the tax never attached to it. You did not destroy it and you did not sell it, which is exactly why the forum poster was confused, but for tax purposes that is fine. Ordinary evaporative loss in storage is an allowable loss. You record it, you report it, and you are not assessed tax on it. The regulations governing losses on bonded premises are in 27 CFR Part 19, viewable at ecfr.gov, and the operational reports where you account for inventory and losses are described in TTB's reporting guidance at ttb.gov.
When does a storage loss actually become taxable?
Allowable does not mean automatic. A loss is taxed when it is not allowable, and there are real categories where that happens. This is the line every DSP needs to understand.
Losses caused by theft, by negligence, fraud, or other unlawful act, or losses that the distiller simply cannot account for, are a different matter. If your gauging shows a barrel is short by an amount that ordinary evaporation does not explain, TTB can treat the unexplained shortage as if the spirit was removed without tax determination, and it becomes taxable. The protection for ordinary evaporation rests on the loss being genuinely ordinary and genuinely documented. An excessive or unexplained shortage does not get that protection.
This is the practical reason TTB expects to see losses, and also expects them to be reasonable and recorded. A barrel that shows zero loss after two years is as suspicious as one that shows fifty percent. The way you protect yourself is the same in both directions: gauge consistently, record honestly, and keep the paper trail that shows your reported losses track with normal evaporation for your climate and warehouse.
Note also that voluntary destruction is its own process. If you have to destroy spirits in bond, there are specific procedures and notice requirements for doing so without tax liability. That is separate from evaporation and is not what is happening when the angels take their share, but it is worth knowing the two paths exist and are treated differently.
How do I record evaporation loss correctly?
The workflow distillers describe is straightforward once you have done it a few times. At the end of each calendar quarter, you physically gauge your barrels in the storage account and compute the loss from the change in wine gallons, calculated at the original barreling proof. You record that loss on your storage operational report. You do not reproof at this stage. When spirit later transfers out of the storage account, you reproof and record any additional loss at that point.
The accounting principle underneath all of this is the proof gallon. A proof gallon is a gallon of spirit at 100 proof, so it measures the actual alcohol, not just the volume of liquid. Your tax liability and your inventory of record both run on proof gallons, which is why getting the wine-gallon-to-proof-gallon conversion right is the foundation of clean reporting. We cover that conversion in detail in Proof gallons vs wine gallons, and the broader question of operating under bond in Bonded warehouse and the DSP bond, explained.
A few habits keep this from becoming a fire drill at audit time. Mark your barrels permanently, because chalk washes off when you spray barrels to keep them tight, and a lost barrel ID is a lost audit trail. Gauge on a consistent schedule rather than scrambling at quarter close. And reconcile your reported losses against what is normal for your climate, so that if a number looks off you find out before TTB does. Losses that are real, ordinary, and documented are not your problem. Losses you cannot explain are.
The bottom line
The angel share is a cost of making aged spirits, not a tax event. Ordinary evaporation in your bonded storage account is an allowable loss: you gauge it, you record it at the original barreling proof, and you are not assessed federal excise tax on spirit that was never removed for sale. Tax attaches when you remove from bond, on the proof gallons you actually take out, and the only losses that become taxable are the ones you cannot account for or that come from theft or negligence. Always confirm the specifics against current TTB guidance and your own regulatory counsel before you file.
The hard part in practice is not the rule, it is keeping the records straight across hundreds or thousands of barrels so the numbers always reconcile. Spirit Sight tracks proof gallons, quarterly gauges, and storage losses per barrel so your operational reports tie out to your physical inventory without a spreadsheet rebuild every quarter.