🥃 Cask Strength Whisky
Whisky bottled undiluted from the cask: under US rules “cask strength” may be lower than the cask strength by no more than 1% ABV.
Cask strength whisky (cask strength, barrel proof) is whisky bottled after maturation undiluted, or almost so, so the bottle holds roughly the strength of the cask. In the United States the term is defined by regulation: the bottling strength may be lower than the cask strength by no more than two degrees proof, that is 1% ABV.
This is the rule 27 CFR § 5.87, adopted in 2022; it grew out of ATF ruling 79-9 (1979). The same rule defines related terms: “original proof”, “original cask strength” or “entry proof” mean that the strength in the bottle equals the strength at which the spirit was filled into the cask. EU Regulation 2019/787 has no separate definition, and the Scotch Whisky technical file merely forbids changing the strength of “cask strength” Scotch after maturation.
Cask strength depends on how the spirit was filled and where it matured. Irish grain spirit is reduced before the cask, usually to 63–70% ABV, while US bourbon is filled at no more than 62.5% ABV. In Scotland’s cool, damp climate relatively more alcohol evaporates and the strength in the cask falls; in a warm, dry one more water goes and the strength can rise. In Scotland about 2% of the spirit disappears from a cask each year on average.
Ordinary whisky is diluted with water to the required strength before bottling, in the EU to no less than 40% ABV. The technical files for Scotch and Irish whiskey explain that when chilled, or after water or ice is added, whisky can turn cloudy because of esters from the cask. That is why much whisky is chill-filtered, but only to prevent haze, without removing colour, taste or aroma.
Why it matters to you. Cask strength means more ethanol in every serving than the usual 40% ABV. Check the exact figure on the label: outside the US “cask strength” has no legal definition. A slight haze after adding water is natural. The WHO reminds us that there is no safe dose of alcohol.
Facts
| Legal basis | USA: 27 CFR § 5.87 (since 2022; earlier ATF ruling 79-9, 1979); no separate definition in the EU |
|---|---|
| Alcohol (% vol.) | as in the cask; in the US at bottling no more than 2° proof (1% ABV) lower; in the EU for whisky no less than 40% ABV |
| Cask type | wooden casks; for EU whisky, oak of up to 700 l |
| Minimum maturation | according to the rules of the type of whisky; in the EU 3 years or more |
| EU category | 2 “Whisky/Whiskey” (the term is not separately regulated) |
How it connects to Spirits
🥃 Cask Strength Whisky → kind of → 🥃 Whisky → kind of → 🥃 Spirits
Links
- Next step
- 🧪 Water
- Packed in
- 🍷 Oak barrel, 🍷 Wine label
- Works with
- 🍷 Cooper
- What it contains
- 🍷 Ethanol
- What it affects
- 🍷 Alcohol and health, 🍷 Drunk driving
- Part of
- 🥃 Whisky
- Similar and different
- 🥃 Single Malt Scotch Whisky, 🥃 Straight bourbon whiskey
- In other topics
- 🏷️ Oak ageing, 🍷 En rama Sherry
Frequently asked questions
What strength does cask strength whisky have?
There is no single figure: it equals the strength of the particular cask. Under US rules the bottling may be lower than the cask strength by no more than two degrees proof, that is 1% ABV.
Is it true that “cask strength” always means whisky from a single cask?
No. Rule 27 CFR § 5.87 concerns only the strength at bottling, not the number of casks. Single-cask whisky is a different concept, which this term does not guarantee.
How does “barrel proof” differ from “original proof”?
“Barrel proof” and “cask strength” mean the strength as when drawn from the barrel, with a tolerance of 2° proof. “Original proof”, “original cask strength” and “entry proof” mean that the strength in the bottle equals the strength at which the spirit was filled into the cask.
Why does the strength in a cask vary?
Because of the filling strength and the climate of the warehouse. The Scotch technical file explains: in damp, cool Scotland relatively more alcohol evaporates and the strength falls, while in a warm, dry climate it is water that goes and the strength rises.
Why does whisky turn cloudy when water or ice is added?
Some of the long-chain esters that came from the cask drop out of solution when cooled or diluted. To avoid this, much whisky is chill-filtered before bottling; removing taste and colour in the process is forbidden.
What to read next
- 🍷 Alcohol and health — Alcohol in any drink is harmful in large amounts, and the risks grow with the quantity.
- 🍷 Oak barrel — A wooden barrel of oak staves in which wine matures and breathes.
- 🍷 Cooper — A craftsman who makes barrels from oak staves.
- 🥃 Single Malt Scotch Whisky — Scotch from a single distillery: only malted barley, water and copper pot stills; at least 3 years in oak, 40% vol. or more.
- 🏷️ Oak ageing — Wine matures in oak barrels and gains aromas of vanilla, toast and spice.
Similar
🥃 Japanese whisky · 🥃 Corn whiskey · 🥃 Straight bourbon whiskey · 🥃 Straight rye whiskey · 🥃 Canadian whisky · 🥃 Irish Grain Whiskey
⚠️ Spirit drinks contain alcohol and are for adults only. Alcohol harms health. Do not drink during pregnancy or before driving; check the label for ingredients and possible allergens.
Sources
- 27 CFR § 5.87 «Barrel Proof» and similar terms (USA, TTB), text via Cornell LII
- T.D. TTB-176, 87 FR 7526 (09.02.2022): Modernization of the Labeling and Advertising Regulations for Distilled Spirits and Malt Beverages, part «Barrel Proof and Similar Terms»
- ATF Ruling 79-9: «Original Proof», «Barrel Proof» on distilled spirits labels (TTB copy, last updated 02.05.2024; archived)
- Technical File for Scotch Whisky, June 2019 (DEFRA, GI)
- Technical File: Irish Whiskey / Uisce Beatha Eireannach / Irish Whisky, Department of Agriculture, Food and the Marine, Oct 2014 (copy on GOV.UK)
- 27 CFR § 5.143 Whisky — standards of identity, Tables 1–2 (USA, TTB), text via Cornell LII
- WHO/Europe: No level of alcohol consumption is safe for our health (04.01.2023)