Sherry and bourbon casks are the two most common cask types in whisky - and they produce distinctly different results. A well-chosen cask, matched to a distillery's style and left for the right length of time, is a matter of real craft.

Quick answer: sherry casks used in whisky are usually American oak seasoned in Spain with sherry - genuine ex-solera sherry casks are rare - and they give dried fruit, spice, nuts and dark colour, with intensity depending on fill number. Bourbon casks are American white oak, previously used to age bourbon (which by US law must use new oak), and their flavour balance shifts across first, second and third fill - not just first-fill. Sherry casks generally lean rich and dark; bourbon casks lean bright and sweet.

Sherry casks

• Oak type varies — often assumed to be European, but most sherry casks used in whisky today are actually American oak

• Seasoned with Spanish sherry (Oloroso, PX, Cream Sherry)

• Typically reused multiple times

• Flavour intensity depends heavily on fill number, not just cask type alone

It's worth separating two things that get conflated under "sherry cask." Most of the industry uses sherry-seasoned casks. A much smaller number are genuine ex-solera casks — ones that actually matured sherry itself.

Casks used to age sherry in the solera system need to stay relatively neutral, so they don't dominate the sherry with wood character — the opposite of what most whisky makers want. So the majority of "sherry casks" in whisky are purpose-built: bought new or near-new, shipped to Spain, seasoned with sherry or a sherry-style liquid for a set period, then sent on to be filled with whisky.

Genuine ex-solera casks — ones that held ageing sherry for years or decades before whisky ever touched them — are much rarer, and prized for it. Our Fielden bottling, for example, was finished in a 45-year-old ex-solera Oloroso sherry cask from a bodega in Sanlúcar de Barrameda — a genuine rarity, given how few true ex-solera casks make it into whisky at all.

Bourbon Casks

• American white oak

• Previously aged bourbon, which by US law must be matured in new American White Oak

• Fill number varies — first, second and third fill casks each give a different flavour balance

• Flavours: vanilla, honey, coconut, toasted almond

It's a common assumption that bourbon casks used for whisky are always first-fill. They're not. Third-fill casks combined with a long maturation are, for many distillers, the ideal pairing — the wood has less left to give, so the spirit can mature for longer without tipping into cask dominance and tasting simply of wood. First-fill delivers more overt vanilla and coconut, faster, but risks getting there before the spirit's own character has had a say.

In short: sherry casks give richness and depth; bourbon casks give brightness and sweetness.

One sherry-matured, one bourbon-matured whisky from each country, so you can taste the cask difference directly.

• Sherry cask — The Heart Cut #24 Ardnamurchan Matured in an PX Sherry cask. 50/50 popcorn, toffee and a light coastal smoke.
• Bourbon cask — Glenmorangie 12 Year Old Matured in first-fill and refill bourbon casks. Creamy vanilla, citrus, honey, peach.

Comparison: #24 Ardnamurchan is matured in the sweetest of sherry casks with a smoky lift ; Glenmorangie shows what careful bourbon-cask ageing does for sweetness and lift. Two highland distilleries, two different approaches.

• Sherry cask — Boann Single Malt PX Cask Single pot still Irish whiskey from Boann Distillery, matured and finished in PX sherry casks made from both European oak and chestnut. Stewed plum, date syrup, nutmeg, velvet texture.
• Bourbon cask — Clonakilty Single Malt Bourbon Cask Matured in first-fill bourbon barrels. Lemon peel, green apple, vanilla pod, honey.

Comparison: Boann PX is indulgent and dessert-like; Clonakilty is fresh and fruit-forward — a clean example of how cask sets the mood of a dram.

• Sherry cask — The Cotswolds Sherry Cask Single Malt Matured in Oloroso and PX casks. Jammy red berries, treacle tart, cinnamon, toasted almond.
• Bourbon cask — White Peak Wire Works Bourbon Barrel Lightly peated, matured in ex-bourbon barrels from Heaven Hill. Vanilla cheesecake, lemon, candied ginger, peach, a trace of smoke.

Comparison: Cotswolds' sherry cask is bold and warming; Wire Works shows how a bourbon cask can bring finesse and clarity even alongside light peat.

• Sherry cask — Akashi Blended Sherry Cask Finish A blend of Japanese and Scotch whisky, finished in sherry casks. Rich and warming.

• Bourbon cask — Kanosuke Double Distillery A blend of single pot still and single malt from Kanosuke Distillery on Kagoshima's coast, matured across ex-bourbon, new American oak and ex-shōchū casks. Sweet toffee, honey, melon, banana, spice.

Comparison: Japanese whisky tends to sit at a higher price point, and many bottles blend cask styles rather than committing to one — Kanosuke is a good example of that layered approach.

• Sherry cask — SirDavis A rye whiskey (51% rye, 49% malted barley), finished in sherry casks. The sherry rounds out the rye's spice and adds dark chocolate, toasted nuts, dried fruit.
• Bourbon cask — Elijah Craig Small Batch US law requires new American oak for bourbon, which is why so many of the ex-bourbon casks used elsewhere in this list originate in America — Heaven Hill, Elijah Craig's distillery, is one of the most common sources. Classic bourbon notes: vanilla, coconut, dried fruit, toffee.

Comparison: because American whiskey law requires new oak for bourbon, sherry shows up here as a finishing flourish rather than a primary maturation cask — intense sweetness meets nutty, wine-cask complexity.