Today, we’re going sherry mad with a close look at whisky aged in oloroso casks. Think of all those wonderful flavours of molasses, Brazil nuts, and chocolate – they come from the spirit, the wood and the sherry interacting in magical and often quite complicated ways. We’re going to take a good look at this process and then recommend some great oloroso cask whiskies from Scotland, Ireland and England. 

Are you ready? Let’s dive into some oloroso sherry!

Oloroso sherry casks

Sherry maturing at Bodegas Estevez

What is oloroso sherry?

The word ‘oloroso’ means pungent in Spanish, or fragrant depending on who you are talking to. It’s made from later pressings of the grapes which contain tannin from the skins producing a full-bodied style of wine, very different to the delicate fino. These impurities in the juice means that the protective flor, the layer of yeast on the top of the sherry, does not form. To well and truly make sure that no flor forms, the wine is fortified to about 20% ABV. 

So oloroso sherries age with oxygen contact. A fino is like an apple with clingfilm on, it keeps its colour and freshnes, whereas an oloroso is like an uncovered apple, it oxidises and turns brown resulting in an earthy rich style of wine with those flavours I mentioned earlier like nuts, chocolate etc. The older the wine, the more intense the flavours.

Oloroso sherry

They love an oloroso sherry cask at Tamdhu

Is oloroso sweet?

Oloroso are naturally dry wines but they are often sweetened with PX – a concentrated sweet style of sherry made from dried grapes – which brings raisins, dates and orange peel aromas to the already heady oloroso party.

What I am trying to say is that olorosos are packed with flavour. The most popular styles of sherry exported to cold countries like Harvey’s Bristol Cream are based on sweetened oloroso sherry blended with some other things. 

How does the oloroso get into the whisky?

Huge amounts of sherry used to be shipped to Britain and Ireland every year in wooden barrels known as transport casks which were usually made from cheap and easy to work American oak. The wine was bottled by merchants, pubs, hotels etc. The empty casks were then used to store whisky in and it was noted how good the resulting spirit tasted. By the late 19th century, sherry cask ageing had become vitally important for the flavour of Scotch and Irish whisky.

This went on happily until 1986 and Spain joined the European Economic Community which decreed that wines with specific designations had to be bottled in their home countries. The supply of sherry casks dried up but there had already been something of a shortage caused by the decline in popularity of sherry.

Oloroso sherry casks

Richard Paterson from Dalmore – loves an oloroso sherry cask

Sherry seasoning

The slack was taken up by bourbon casks from America but distillers and blenders in Scotland and Ireland still needed a dose of sherry to maintain their classic styles. 

The answer was something called paxarette – concentrated and fortified grape juice that for a short time was used to rejuvenate old sherry casks and season new ones. Until it turned out to make horrible whisky so the SWA banned it in 1990. 

So the whisky industry began to get casks seasoned to order in Spain and shipped over. With the decline in sherry consumption, this has proved a good bit of business for the sherry houses. Diageo actually has its own ‘bodega’ at Carsebridge in Central Scotland where it seasons casks with whisky. These are either new oak or older sherry casks that need a bit of perking up. 

The vast majority of sherry used for seasoning casks is oloroso, sweet or dry. You also see quite a lot of PX (the sweetest kind of sherry) casks. The more delicate styles of sherry: manzanilla, fino and amontillado are rarely used for seasoning casks – perhaps because they are more in-demand by drinkers or because they don’t deliver the flavours that whisky blenders want. If a whisky says its sherry cask, then 9 times out of 10, it’s going to be oloroso. 

Gonzalez Byass bodega in Jerez

Gonzalez Byass bodega in Jerez home of Matusalem sherry

But there’s sherry and there’s sherry

The key distinction between the old system of using transport casks and modern seasoned sherry casks lies in the age and purpose of the sherry used. Transport casks held mature sherry, ready to be bottled and sold. In contrast, the sherry used in modern seasoning processes is typically younger and is often not of a quality to be sold for drinking. Once it has served its seasoning purpose, it’s not normally drinkable so it may be distilled into brandy or turned into sherry vinegar.

Many sherry-seasoned casks will use a simple, probably sweetened wine to give simple sweet flavours. Some distillers, however, specific something a bit more up-market. Dalmore uses casks that previously held Matusalem sherry from Gonzalez Byass – an award-winning wine that sells for around £27 for a half bottle. Tamdhu also takes its sherry very seriously. It uses a good quality five year old oloroso and the seasoning process lasts two years.

A sherry cask isn’t simply a sherry cask

The term ‘oloroso sherry cask’ might sound simple but there are a number of complicating factors at play.

-What size is the cask? Smaller casks will give more sherry influence. 

-Is it European or American oak? Many of the flavours that people think of as typically sherry like spices, actually come from the wood.

-What quality of sherry was used to season? Something of commercial quality or a cheap seasoning wine?

-How long was the sherry in the wood for?

-Is the cask refill or first-fill? The sherry and wood influences deteriorate after each use.

-How long was the whisky in the sherry cask for? Some whiskies are aged entirely in sherry casks whereas others are just finished. 

So now you have lots of questions to ask when you visit a distillery which will make you look very clever indeed.

Here are a few of our favourite oloroso cask whiskies:

Oloroso cask whiskies

Olorosum – the name is a clue

Olorosum 10 Year Old Whisky 70cl

Superb single malt from a secret Speyside distillery. As you might have guessed from the name, Olorosum is a splendidly sherried affair. The 10-year-old single malt was treated to an extremely generous finish in oloroso sherry casks before being bottled up without added colour or chill filtration at a hearty 54.7% ABV. 

Seaweed & Aeons & Digging & Fire 10 Year Old Whisky 70cl

This right here is a 10-year-old single malt from an undisclosed distillery on Islay, with 25% of it having been finished in first-fill oloroso sherry casks, and bestowed the decidedly descriptive name Seaweed & Aeons & Digging & Fire. If those four words (and three ampersands) aren’t quite enough of an explanation of what this expression is all about, here are a few more: stripped-back, smoky, complex, a bit sherried, balanced, coastal..

Redbreast 12 Year Old Whiskey 70cl

A delightful single pot still Irish whiskey, Redbreast 12 Year Old is highly praised by a host of notable critics. Distilled at the Midleton site from malted and unmalted barley, it’s then matured in a combination of American oak bourbon barrels and Spanish oak oloroso sherry butts. 

Tamdhu 15 Year Old

Tamdhu is well-known and much-adored for its excellent use of sherry casks, and those of you with a penchant for single malt with heavy sherry influence will be delighted to know that the distillery’s 15 Year Old expression continues that theme. This one has spent is maturation in oloroso sherry casks, resulting in generous helpings of dark fruit and Christmas spice.

Cotswolds Sherry Cask Single Malt Whisky 70cl

A well-sherried expression from the Cotswolds Distillery – which you probably guessed from the name! Distilled from locally-grown barley, this one was then matured in a combination of American and Spanish oak hogsheads and butts, seasoned with oloroso and Pedro Ximénez sherry.