Mighty Oaken Cask #4: Sherry Butt, the Cask that Made Whisky

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Mighty Oaken Cask #4: Sherry Butt, the Cask that Made Whisky

July Outturn 2024 Feature Article

Words: Chris Middleton


For two hundred years, the ex-sherry cask was the preferred and universal container for maturing Scotch and Irish whisky. Its popularity was due to its strong and delectable sherry influence imbued into the Gaelic spirit uisge beatha, whisky, in the English vernacular. Sherry imparted distinctive vinous flavours and served as the sensory bridge between brandy and wine, especially in the populous English market well-accustomed to cognac and sherry. By the 1870s, whisky had established itself as Britain’s leading spirit.

Sherry is a southern Spanish wine blended with a small amount of neutral grape spirit, or young brandy, to preserve the wine for transport and longevity while adding flavour compounds. Sherry is more than another fortified wine as it is matured by biological and oxidation aging processes, giving the sherry varietals distinctive flavour profiles. The flor layer biologically ages Fino, Manzanillo and Amontillado styles, bringing nutty, apple and citrus nuances. Oxidised sherries like Oloroso and Pedro Ximenes deliver sweeter, bolder and raisin-infused flavours.

Britain’s wars with France during the 18th and early 19th centuries forced Great Britain to form alliances and trade treaties with Spain, which ceded the sherry flavour shift to the two major British whisky industries. Irish and Scottish distillers obtained a supply of empty ex-sherry butts from this wine trade. The more advanced Dublin distilleries began prescribing sherry butts in the 1780s as export demand grew in England. Scotland’s distilleries had no meaningful export business, except grain spirit for rectification in England until the 1850s; by then, sherry casks were de rigueur for Scotch. Until the 19th century, distilleries, spirit dealers and even Scottish estates cellared negligible volumes of whisky for maturation. Instead, most whisky was kept in stoneware crocks or flagons, commonly drunk raw or in toddies. In the Highlands, where much illicit distilling occurred, small anker casks were carried by pony or hidden in wagons for local sale and consumption.


By 1830, sherry became Britain’s most-consumed wine, and in the 1860s, it commanded a 42% share of Britain’s total wine sales. The Spanish sherry trade shipped export butts (500 litres), peaking in 1874 at 68,467 butts. Over two and halfmillion butts were imported to Britain throughout the 19th century; some were sent back to Jerez in a circular trade for reuse by the bodegas; many were re-coopered by the whisky industry into smaller hogshead and barrel capacities for recycling, even refilling for a second or third time. Scotch production doubled between 1874 and 1899, while sherry casks fell by a third. This difference-delta compelled distilleries to supplement their sherry cask inventory with new, virgin casks aggressively treated with lime, caustic soda and steam to extract tannin and other undesirable compounds. New make spirit was stored in new wood for a year or two before finishing in an ex-sherry cask for another year or more. The pleasing flavours of sherried whisky fuelled exports to England and expatriate colonies throughout the British Empire, and after the Excise on Spirits Act of 1860 permitted blended whisky, the industry boomed.

Changing consumer tastes to dry-style table wines, aggravated by two World Wars, the Spanish Civil War and the Depression, drove sherry’s long-term decline since 1875. Since 1970, the global sales for sherry have continued to retreat, falling by 80%. The lack of consumer demand for sherry exacerbated the shortage of casks, making them an increasingly more expensive and diminishing resource. During the 1930s, the cost of a butt increased eightfold. Fortuitously, the American whisky industry, after Prohibition, the Depression and the Second World War, began generating excess ex-bourbon barrels in the 1960s. U.S. regulations since 1936 permit single usage of a ‘charred white oak container’ to be labelled straight whisky. These surpluses of bourbon barrels found a second life in the British Isles. 


Sherried whisky was originally a wine-driven spirit rather than oak-influenced. That’s because oak extractives in sherry are avoided by Jerez vintners, preferring exhausted and inert casks for maturation — a flavour legacy inherited by sherried whisky until the 1870s. For the next hundred years, export sherry butts and flavour treatments, such as adding prune juice and ersatz-sherry flavourings to the whisky, and the introduction of pneumatic cask treatments (paxarette) in the 1880s, helped sustain sherried whisky production until 1986. That is when the Spanish government banned the shipment of bulk sherry in wood to prevent fraud and adulteration in export market bottlings. In response, bodegas and Spanish cooperages produced faux-sherry casks for the whisky industry to circumnavigate this loss of sherried wood by briefly seasoning new casks with cheap bulk sherry. Unlike long-seasoned sherry butts, the new oak character of these young casks made its oaken wood presence discernible on the palate, with European oak rendering more spice, dried fruits, and slightly astringent mouthfeel. The more popular American oak imparts hints of vanilla, coconut, and sweetness on the palate.

While specially prepared sherry casks have helped fill the void over the past forty years, today, over 95% of Scotch’s first fill is now ex-bourbon. A small percentage of whisky production is sherried whisky, with these modern oaken whiskies responsible for the ‘sherry bombs’ so popular with contemporary malt drinkers.

Australian coda: Australia has produced fortified wines since the 1890s. By 1950, 85% of domestic wine consumption was fortified wines, mainly local sherry, followed by domestic port and vermouth. Fortified wine continued to dominate the wine industry until 1970 when the demand for table wines replaced fortified styles. With the European Union negotiating the protection of their regional wine appellations and styles under Geographical Indication, Australian wine producers were no longer permitted to use the Spanish term ‘Sherry’ after September 2010. Instead, the new category trademark, Apera, was adopted for this Australian class of fortified wine. Australian Apera consumption is reduced to a trickle, less than 0.5% of volume wine sales, with very few retired casks available each dumping season for local distilleries to refill with whisky. Some of Australia’s larger distilleries maturing expressions of whisky in Apera casks have adopted the Spanish technique of filling new casks with Apera wine to impregnate the staves with its vinous flavour.

This is the 4th instalment in the Mighty Oaken series by Chris Middleton. The series can be read online at smws.com.au/news.


This article is featured in July 2024 Outturn — bottles will be available to purchase on Friday the 5th of July at midday AEST exclusively to members of The Scotch Malt Whisky Society. Not a member? Click here to learn more about the world’s most colourful whisky club.


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