First Fill and Refill Casks
At Loch Lomond, a cask can serve through three malt fills and six grain fills, with two rejuvenation treatments along the way. At six years per fill, the producer puts that working life at over 50 years.[5] A cask’s first filling of Scotch is just one chapter in its life.
A first-fill cask is a used cask receiving Scotch whisky for the first time, not brand-new oak. Refill casks have already matured Scotch, though producers draw different boundaries between “second fill” and “refill”. Repeated use generally leaves fewer wood compounds available for extraction. That makes refill a different maturation tool, not an inferior one.[1][2][3][9]
What first fill and refill mean
“First fill” counts Scotch fillings, not every liquid a cask has held. A first-fill ex-bourbon cask has already matured bourbon. Its first Scotch filling marks a new stage in its working life, not the beginning of it.[2][3][9]
Kilchoman sets out a straightforward distinction: the first time it uses a cask, it calls it first fill. Once it has used that cask more than once, it calls it refill.[2]
The Scotch Malt Whisky Society draws a finer distinction. A cask that has matured Scotch once becomes “second fill” on its next use; “refill” means at least two previous whisky fillings.[9] Verdict: Disputed. These different boundaries mean “refill” alone cannot give an exact fill count. Kilchoman explains its usage in its 2022 account at https://www.kilchomandistillery.com/distillery-news/casks-first-fill-v-refill/; the Society explains its usage in its undated account at https://smws.com/unfiltered/flavour-focus-maturation. The earliest source of the terminology is not established from the sources checked.[2][9]
| Description | Kilchoman’s usage | SMWS usage |
|---|---|---|
| First fill | First use by the distillery [2] | First Scotch filling after another liquid [9] |
| Second fill | Included under refill [2] | One previous Scotch filling [9] |
| Refill | Used by the distillery more than once [2] | At least two previous whisky fillings [9] |
If the exact filling history matters, look for the producer’s explanation. Neither account uses first fill to mean virgin oak, which belongs to the separate subject of whisky matured in new oak.[2][9]
Previous contents and filling number answer different questions. “Ex-bourbon” tells you about an earlier maturation use; “first fill” identifies the first Scotch use of that already-used cask.[3][9] Read the two descriptions together, rather than treating them as alternatives.
Why use a cask that has already held something else?
Used oak helps keep wood from overwhelming the whisky. The Scotch Whisky Technical File says Scotch is usually matured in casks previously used for other spirits or wines “so that the flavour of the wood does not overpower the whisky”. It describes cask selection as a decision for the chief blender, seeking a particular character in the finished whisky.[1]
The aim, then, is not simply to extract as much as possible. It is to get the contribution the blender wants. A less extractive cask has a deliberate role: it need not be a substitute for a more active one.[1][3]
Previous contents do not mean that the cask should still contain a quantity of its former drink. The Scotch Whisky Technical File states that, for Scotch maturation in Scotland, casks must be empty of their previous contents before being filled with Scotch or spirit destined to become Scotch.[1] Using a previously seasoned vessel is distinct from adding the drink it once held.
For the wider relationship between spirit and wood, read how whisky matures in oak. Here, the focus is reuse: what remains available in the oak after successive maturations, and how that changes the cask’s contribution.[3]
What repeated use does to oak
Repeated maturation draws down the oak’s supply of extractable compounds. Conner, Paterson and Piggott examined American white oak, Quercus alba, from four cask categories: new charred, first fill, second fill and exhausted. In their study, first fill meant a used bourbon cask; the categories represented progressively greater maturation use.[3]
They found declining levels of free guaiacyl acids and aldehydes, a group of wood compounds. These figures measure compounds in the wood, not flavour intensity in the glass.[3]
| Cask category in the study | Free guaiacyl acids and aldehydes |
|---|---|
| New charred | 0.19 µmol/g of wood [3] |
| First fill, used bourbon cask | 0.14 µmol/g of wood [3] |
| Second fill | 0.08 µmol/g of wood [3] |
| Exhausted | 0.06 µmol/g of wood [3] |
“Exhausted” did not mean the wood had simply lost its lignin, a structural component. The study found no significant delignification. Low concentrations of free, extractable compounds were the better indicator of exhaustion.[3]
The figures cannot be turned into a percentage comparison of first-fill and refill flavour. They describe one group of compounds in sampled oak, rather than the cask’s whole sensory contribution.[3]
George Reazin’s 1981 research also traced declining effects with reuse. Charring made barrel wood more reactive, producing higher congener levels on the first filling than an uncharred barrel. Congeners are compounds other than water and ethanol that contribute to spirit character. With repeated use, those levels approached the levels associated with the uncharred barrel.[4]
What the difference means for flavour
Spicy, vanilla and woody descriptors featured in a 1993 study of Scotch distillates matured for their first three years in casks with different histories typical of industrial practice. The researchers found differences in both wood-derived components and sensory assessments.[12]
Cask history, in other words, has measurable sensory consequences. The study compared particular histories, however, rather than finding a single flavour profile shared by every first-fill cask or another shared by every refill.[12]
The University of Glasgow places previous use alongside cask size and shape as factors that help each cask mature “in its own way, and in its own time”.[11] Filling number is a useful clue within the full cask description, not a replacement for it.
A first-fill statement tells you about the wood’s use history. How woody the whisky tastes, and whether that contribution suits a particular reader, cannot be settled by that statement alone.[3][11][12]
How many times can a cask be filled?
There is no single working life for every cask. Loch Lomond says most distilleries use a cask three times. In a 2020 report, Speyside Cooperage’s Ronnie Grant described three or four fills, with further fills possible after repair and rejuvenation.[5][6]
Loch Lomond’s own process takes reuse considerably further.
Story box: Nine fills at Loch Lomond
Verdict: Documented, producer's account. Loch Lomond describes three malt fills followed by six grain fills, with two rejuvenation treatments. At six years per fill, it says the cask is in use for over 50 years. This describes its own process, rather than a standard for Scotch.[5]
Source and claim mapping: Loch Lomond Whiskies, De-char and Re-char Process Explained, supplies the fill sequence, treatments and duration: https://us.lochlomondwhiskies.com/blogs/news/de-char-re-char-at-the-cooperage. The source is undated; the sheet records a check in November 2026.
Verdict: Disputed. Published accounts differ on useful cask life. Ronnie Grant of Speyside Cooperage described up to 50 or 60 years, with repair and rejuvenation allowing further fills. A Cambus Cooperage guide quoted by VinePair described some 100 years with rejuvenation.[6][13] Neither establishes a universal working life. The earlier of the two supplied accounts is VinePair's 2017 article: https://vinepair.com/articles/bourbon-to-scotch-barrel-cooperage/. Grant's account appeared in 2020: https://www.pressandjournal.co.uk/fp/lifestyle/2760883/speyside-cooperage-nae-coopers-nae-whisky/.
Kilchoman offers a practical decision point: it assesses whether an individual cask has the quality to continue into a second or third fill.[2] The completed fill count matters, but the producer’s judgement determines whether that cask carries on.
Rejuvenation changes the history again
A used cask can receive treatment to extend its useful maturation life. Loch Lomond describes removing old char and recharring the interior; Speyside Cooperage says repair and rejuvenation can permit further fills.[5][6] These are cooperage processes, not instructions for treating a cask at home.
That treatment becomes part of the cask’s history alongside its earlier maturations. Filling number alone no longer tells the whole story. Reazin’s paper discusses recharring alongside the changing chemical effects of barrel reuse, underlining why both use and treatment matter.[4]
For the processes themselves, see rejuvenated casks and recharring. Keep the two pieces of information distinct: “refill” describes reuse, but does not account for every treatment a cask may have received.[2][4][9]
Where to go next
- Ex-Bourbon Casks: understand the earlier use behind many first-fill descriptions.
- Sherry Casks: Oloroso, PX and Fino: explore a different previous-content description.
- Cask Finishing and Double Maturation: distinguish changing casks from counting their previous fills.
Sources
[1] UK Government. Technical File for Scotch Whisky, June 2019.
https://assets.publishing.service.gov.uk/media/5fd36667e90e07662ed92c85/Scotch_Whisky_Technical_File_-_June_2019.pdf
[2] Kilchoman Distillery. Casks: First Fill v Refill, 8 September 2022. Producer’s account.
https://www.kilchomandistillery.com/distillery-news/casks-first-fill-v-refill/
[3] Conner, J. M., Paterson, A. and Piggott, J. R. Analysis of Lignin from Oak Casks Used for the Maturation of Scotch Whisky. University of Strathclyde paper hosted on a University of Edinburgh webpage; received 14 February 1992, accepted 17 July 1999; journal and publication year not stated on the hosted page.
https://www.dcs.ed.ac.uk/home/jhb/whisky/papers/caskanal.htm
[4] Reazin, G. H. Chemical Mechanisms of Whiskey Maturation. American Journal of Enology and Viticulture, volume 32, issue 4, pages 283 to 289, 1981. Abstract.
https://www.ajevonline.org/content/32/4/283
[5] Loch Lomond Whiskies. De-char and Re-char Process Explained, undated. Producer’s account.
https://us.lochlomondwhiskies.com/blogs/news/de-char-re-char-at-the-cooperage
[6] Ritchie, Gayle. Speyside Cooperage: ‘Nae coopers, nae whisky!’ Press and Journal, 22 December 2020.
https://www.pressandjournal.co.uk/fp/lifestyle/2760883/speyside-cooperage-nae-coopers-nae-whisky/
[9] Scotch Malt Whisky Society. Flavour Focus: Maturation, undated. Trade account.
https://smws.com/unfiltered/flavour-focus-maturation
[11] University of Glasgow. New ageing test could be gold standard for whisky producers, 11 October 2022.
https://www.gla.ac.uk/news/archiveofnews/2022/october/headline_886322_en.html
[12] Piggott, J. R., Conner, J. M., Paterson, A. and Clyne, J. Effects on Scotch whisky composition and flavour of maturation in oak casks with varying histories. International Journal of Food Science and Technology, volume 28, issue 3, pages 303 to 318, 1993. Abstract.
https://academic.oup.com/ijfst/article/28/3/303/7867650
[13] Hines, Nick. Bourbon to Scotch barrel cooperage. VinePair, 3 August 2017. Trade account.
https://vinepair.com/articles/bourbon-to-scotch-barrel-cooperage/
This article is desk research based on the site’s verified fact sheet TOP-A455, distinguishing research findings from producer and trade accounts.
Last checked: November 2026