Master Distiller Blog No.09 — How Many Bottles Does a Cask Make?
David Hsieh
Using cask volumes and the angel’s share to work out how many 700 mL bottles a cask actually yields
By David Hsieh — Master Distiller, Tankyu Distillery | Presenter, Business Whisky Guide Podcast
Adapted from Business Whisky Guide Podcast EP9 — ‘Nearly a decade undercover, even the labels on the labels are wrong (Part II, censored)’.
There are, in practice, only a small number of standard-spec cask sizes used across the Scotch whisky industry. The three you meet most often are the Bourbon Barrel, at about 200 litres; the Hogshead, at about 225 to 230 litres; and the Sherry Butt, at about 500 litres. These are the casks the trade uses for its core-range maturations. Other sizes — the Quarter Cask at around a quarter the usual capacity, the Octave at an eighth — are in use too, but as specialist formats rather than as workhorses.
The standard Scotch bottle is 700 mL: the most widespread export format. The United States is the main exception, where 750 mL bottles are the norm; 500 mL and 200 mL bottles tend to belong to travel-retail and limited editions. For the arithmetic that follows, we will use 700 mL as the reference.
The arithmetic, before the angels take any
Suppose, hypothetically, that the moment a cask is filled with new make spirit, you immediately drain it back out and bottle the lot at 700 mL. A bourbon barrel at 200 litres would give you about 285 bottles; a 230-litre hogshead, about 328 bottles; a 500-litre sherry butt, about 714 bottles.
In real life, no cask delivers that. The cask loses a meaningful fraction of its contents through the wood during maturation, by evaporation — the angel’s share.
The angel’s share
Scotland’s climate is even-tempered year-round, and the trade-average angel’s share comes out at around 2 per cent per year. After year one a full cask has 98 per cent of its liquid left; after year two, 96 per cent; and so on. After ten years, roughly 80 per cent remains; after twenty, about two-thirds; after thirty, around half. The 2-per-cent figure is, of course, an average. Actual loss depends on warehouse geography, where the cask sits in the warehouse, whether the cask has been leaking, the filling strength, and the region — the angel takes a slightly different cut on the Highland mainland, on Islay and in Campbeltown. Two per cent is the working approximation the trade has settled on.
Twenty years on, at cask strength
Apply the figures to a twenty-year-old bourbon barrel and the liquid remaining is around 133 litres. If the cask is bottled at cask strength — no dilution after maturation — those 133 litres yield about 190 bottles of 700 mL cask-strength whisky. A twenty-year-old hogshead would give about 220 bottles; a twenty-year-old sherry butt, about 480 bottles.
This arithmetic offers a simple sanity check against single-cask labels in the wild. If you encounter a bottle labelled ‘20 years old, sherry butt, cask strength’ but the outturn is comfortably above 480 bottles, you can reasonably conclude the whisky is not a true single cask in the strict sense — a single twenty-year-old sherry butt should not be giving much more than 480 bottles — and the bottling probably belongs to the looser category of vatted cask strength, in which multiple casks have been combined.
Going the other way: a twenty-year-old bourbon barrel, declared single cask and cask strength, with an outturn of only 100 bottles — that is also worth noticing. The barrel should theoretically deliver around 190 bottles. An actual 100 means the evaporation loss was much higher than the trade average, and there could be several reasons: a warmer storage position in the warehouse, a leak that opened at some point during the maturation, frequent sampling by the distiller, or trouble in the cooperage or storage chain. The discrepancy does not mean the whisky is bad. It does, though, tell the drinker that there is a story behind the cask. The figures vary, of course, with warehouse conditions, distillery recipe, and whether the bottler has, at any point, redistributed liquid between casks to make up a ‘single cask’ bottling — all of these will shift the picture.
Reading the label
The labels put out by independent bottlers usually carry the full disclosure: distillation date, bottling date, cask number, bottle outturn, and bottling strength. Combined with the cask type, those data points are usually enough to let the drinker check, on the back of an envelope, whether the maturation profile of the cask is consistent with what is being claimed.
Once those numbers are legible to you, a single-cask bottle in the hand becomes something you can have a conversation with.
After all, the appeal of a single cask is precisely the one cask, one world of it — and the right cask waits for the right drinker to find it.
About the author
David Hsieh is master distiller at Tankyu Distillery. He has previously worked as a distiller at several whisky distilleries in Scotland. He holds an MSc in Brewing and Distilling from Heriot-Watt University, and is the host and producer of the Business Whisky Guide podcast, Taiwan's #1 whisky podcast.
About the distillery
Tankyu Distillery is one of Japan's few public-private (公設民営) craft distilleries, located in Higashikawa, Hokkaido. The company was established in 2020, and the distillery opened in August 2025. It produces single malt whisky and craft gin using pristine spring water from the Daisetsuzan mountain range — water so pure that Higashikawa remains the only municipality in Hokkaido without a municipal water supply. Learn more at tankyudistillery.jp/en.
Source
・ Business Whisky Guide podcast EP9 — ‘Nearly a decade undercover, even the labels on the labels are wrong (Part II, censored)’.
Other distilleries, brands and producers mentioned in this article are referenced on the basis of publicly available information and the author’s personal observation, in the spirit of information-sharing rather than commercial comparison or evaluation. The references do not represent the position of Tankyu Distillery.