Spirit Aging Evaporation Loss Calculator
Estimate the volume and alcohol lost during barrel aging of spirits — commonly known as the Angel's Share. Accounts for barrel size, climate, aging duration, and initial fill parameters.
Total liquid volume placed in barrel
Alcohol by volume at fill (40–94.8%)
Standard sizes: 53 gal (200 L), 30 L, 500 L
Minimum 0.25 years (3 months)
Climate drives annual evaporation rate
Upper floors lose more due to heat cycling
New charred oak increases evaporation slightly
Optional: for financial loss estimate
Formulas Used
Compound Evaporation Model:
V(t) = V₀ × (1 − r)ᵗ
- V₀ = initial fill volume (L)
- r = effective annual evaporation rate (fraction)
- t = aging time (years)
Effective Annual Rate:
r = (r_climate + r_warehouse + r_char) × (200 / barrel_size)^0.25
The barrel-size correction reflects the higher surface-area-to-volume ratio of smaller casks.
Pure Alcohol Lost (LAA):
LAA_lost = V₀ × (ABV₀/100) − V(t) × (ABV_final/100)
ABV Drift: Linear approximation based on climate-driven differential evaporation of water vs. ethanol.
Assumptions & References
- Evaporation is modelled as a compound (geometric) decay — each year's loss is a fixed percentage of the remaining volume, not the original fill.
- Base annual rates: Cool ~2%, Temperate ~2.5%, Continental ~4%, Tropical ~6.5% — derived from industry averages (Distilled Spirits Council; Piggott, Paterson & Conner, 1989).
- Barrel size correction uses an empirical (SA/V)^0.25 scaling normalised to a 200 L standard barrel (Neto et al., 2019).
- ABV drift rates are linear approximations; actual drift is non-linear and depends on barrel porosity, humidity, and temperature cycling.
- In cool/temperate climates water evaporates preferentially → ABV rises. In tropical climates ethanol evaporates faster → ABV falls (Conner & Paterson, "A Practical Guide to Whisky Flavour", 2017).
- Model does not account for: barrel leakage, topping-up practices, solvent extraction gains, or blending losses.
- Financial loss is calculated on litres of pure alcohol (LAA) lost, multiplied by the user-supplied value per LAA litre.
- ABV is capped between 40% and 94.8% (legal and physical limits).