September Outturn 2024 Feature Article
Words: Chris Middleton
The most radical sensory change affecting Scotch and Irish whisky happened during the past fifty years. The bourbon barrel invasion usurped sherry casks as the primary maturation container.
As the oaken cask is the main source of whisky flavour, shifting to ex-bourbon profoundly modified whisky’s historical character. Since the 1960s, as sherry wood became even more difficult and expensive to procure, ex-bourbon wood inexorably filled the void. During the first decade of the 21st century, over 95% of first-fill was ex-bourbon barrels. Sherried whisky had defined Scotch and Irish whisky for over two hundred years, but now ex-bourbon reigns supreme.
Two cask factors conspired to make this change. Since the 1880s, Britain’s sherry consumption had been in decline, reducing the quantum of butts for the whisky industry. When Spain joined the E.U., the government had banned the shipping of bulk butts and casks in 1986. The cask trade had already begun to dry up as bodegas increasingly bottled their sherry to prevent fraud overseas. Responding to a scarcity of casks, whisky distillers began new cask treatment programs by filling virgin oak containers with sherry wine for a year or two in the late 1970s. This led to another discernible sensory shift, increasing oak-derived flavours in sherried whiskies.
The other factor was that a year before the Second World War began, the U.S. Congress passed an Act mandating straight whisky ‘must be stored in a charred white oak container’, effective July 1938. Prohibition’s repeal in January 1934 left the U.S. with a shortage of bonded bourbon whisky barrels, lasting until after the Second World War. In North America, dumped barrels were in demand for domestic reuse to age the more popular new class of spirits known as (American) blended whiskey, neutral grain spirit with 20% or more straight whisky. The first experimental shooked (broken down) ex-bourbon barrels sent to Scotland departed from Brooklyn’s Maslow cooperage on VE Day 1945. By the late 1950s, ex-bourbon wood was deemed a viable alternative to sherry. Two-year-old, four-year-old, and older once-used bourbon barrels began serving Scotland’s distilleries. By 1965, two and a half million staves were landing in Britain, scraped of charcoal and reassembled as larger hogsheads by adding several staves with greater capacity to acclimatise the higher proof whisky for longer, cooler and slower maturation. As America’s burgeoning domestic bourbon industry grew from the late 1950s, millions of unwanted barrels became available to Scotch distillers. Ex-bourbon was proving to be a worthy alternative to replace traditional sherry casks in Scotland and Ireland, and relatively inexpensive compared to sherry casks.
American oak was not new to the whisky industry; it had been the preferred cask wood by Spanish sherry wineries since the early 1700s. White oak exports to Europe have been a major source of colonial trade since the 1680s. In 1807, Don Esteban Boulelou wrote, “They (bodegas and cooperages in Jerez and Sanlucar) use oak almost exclusively; they esteem more than any other that which comes from the United States of America,” “next Northern Baltic oak, then Italian, and lastly, Spanish oak.” The sherry butts arriving in Scotland in the late 18th century were mainly American white oak.
North America’s Quercus alba white oak species are less tannic, with pleasing lactone and lignin flavour compounds and sweeter to taste, complementing sherry and whisky. After the 1860 Amended Excise Act opened the floodgates for blended Scotch, production tripled over the next four decades, while sherry imports fell from a peak of 40 million litres in 1873 to 23 million in 1893, with export butts declining by half. In 1900, 49,497 butts of sherry were imported into Britain; however, sherry’s Jerez de la Frontera ports reported their total worldwide exports at 42,565 butts. Spain’s export agents had long sold comparable wines from neighbouring regions as sherry. Not until 1933 did Jerez de la Frontera gain geographic protection for its sherry denomination.
Rum puncheons and port pipes also declined as whisky consumption soared. Distilleries shunned these two cask types as sherry was universally regarded as the superior cask flavour for ‘genuine Scotch whisky.’ Even seasoned new American oak casks, purged of tannins and oaken flavours by steam, chemical washes and other treatment methods, were preferred to other wine or spirit casks.
As sherry’s custom declined, further adverse events reduced production. Phylloxera reached the Jerez district in 1894, devasting harvests for years, followed by trade restrictions caused by the Great War, the Spanish Civil War and the Second World War, all driving down sherry production. As sherry casks became a dwindling resource, ex-bourbon barrels ably served distilleries in the British Isles.
In the 1980s, the growing dominance of ex-bourbon barrels began to inspire new maturation programs, repeating techniques of the late 19th century by offering consumers nuanced flavour differentiation employing sherry cask finishing or double-casking. Another 19th-century ‘sherry wine treatment’ banned after 1988 (paxarette cask) is the subject of the next instalment.
Contracting supply of ex-bourbon barrels has become an increasing concern to the Scotch industry. Over the past two decades, the total production of the traditional Scotch malt distilleries has increased from 111 million litres of pure alcohol in 1981 to 284 million in 2014, estimated in 2023 at 330 million litres. Additional demand comes from over 2,000 new whisky and rum distilleries since 2005. In recent years, the increasing demand for the once bountiful bourbon barrel pipeline has caused prices to double, impacting whisky’s cost of goods. Unlike the annual cycles of barley and other cereals, oak tree and cask maturity is measured by the lifespan of the species that drink whisky.
This is the 5th 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 September 2024 Outturn — bottles will be available to purchase on Friday the 6th of September 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.
