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Sherry cask seasoning - how sherry casks are really made

Whisky matured in a sherry cask is one of the most prized styles - dark, rich, with notes of dried fruit, nuts and spice. But behind the word sherry hides a story that surprises many enthusiasts. Most of today’s sherry casks never held sherry meant for drinking. They are made in a special process called seasoning: a new oak cask is deliberately filled with wine for a year or two, solely to soak the wood, after which the wine is poured out and distilled into brandy or turned into vinegar. This is not a fraud but today’s industry norm. Here is a guide to the truth about sherry casks: what seasoning is, why it replaced the old transport casks and what paxarette was.

In the past: transport casks

Once sherry casks came to whisky almost by chance. In the 19th and early 20th century sherry was transported from Spain to Britain in large oak casks, because it was the handiest packaging. After being emptied in British ports these empty casks, soaked with wine through the long voyage and storage, were cheap and available - so distilleries began to age whisky in them. It was a by-product of the wine trade, not deliberate cask production. This is why old sherry whisky really did mature in casks that had carried wine meant for drinking. This model worked as long as sherry sailed in casks - but that ended, and it was precisely this change that gave birth to today’s seasoning. We cover the role of the cask more in the cask in whisky.

What the law changed

The turning point came in the 1980s. Spain, protecting jobs and the sherry brand, brought in rules requiring sherry to be bottled in its region of origin, around Jerez. From then on it was forbidden to export sherry in bulk in casks for bottling abroad. This overnight removed the source of the old transport casks - since sherry no longer sailed in oak, distilleries lost their natural supply of used casks. And demand for the sherry style did not vanish, it was even growing. So the industry had to invent a new way of getting casks of this character. The answer became seasoning - the deliberate production of casks soaked with wine specially for the whisky industry, independent of the trade in drinking sherry.

What seasoning is

Seasoning is the deliberate soaking of a new oak cask with sherry wine. It looks like this: a cooper in Spain makes a fresh cask from oak, and then sends it to a bodega, where it is filled with sherry - in Spanish this procedure is called envinado. The wine stays inside usually from half a year to two and a half, with one to two years being the standard. During this time the wine penetrates the pores of the wood, giving it colour, tannins and aromas. When seasoning is finished the wine is poured out, and the cask - now soaked with the character of sherry - goes to the distillery for whisky. This is the key difference: the aim is not to make wine but to prepare the cask. The wine here is a means, not a product.

What happens to the wine

The wine used for seasoning ends badly - and deliberately so. After being poured from the cask it is usually re-used for further seasonings, and after a few cycles thrown away. From a legal point of view it cannot be sold as sherry, because it was not made according to the rules of the appellation, and it is not fit to drink anyway - it is tired and drawn out. Usually it is distilled into sherry brandy or turned into wine vinegar. This shows that the wine in seasoning plays a purely technical role: it is to give the cask character, not to reach the glass. For many fans this is surprising, because it spoils the romantic image of a cask full of noble, drinkable sherry. But it is today’s open industry norm, not a hidden shame.

Oloroso, PX and other styles

Various types of sherry are used for seasoning, and the choice affects the profile of the whisky. By far the most common is oloroso - dry or sweetened - because it gives the classic, rich profile of nuts, dried fruit and spice. Very popular too is PX, that is Pedro Ximenez, the sweetest kind of sherry, which adds deep sweetness to the whisky, notes of raisins, figs and molasses. Less often you meet fino or amontillado, giving a lighter, more nutty-salty character. The producer chooses the type of sherry deliberately, designing the flavour of the future whisky, which is why labels carry notes like oloroso cask or PX finish. The type of wine used for seasoning is one of the main levers by which a distillery shapes the final profile. We cover ageing itself more in what a whisky finish is.

A table: transport versus seasoned

Let us gather the two eras of sherry casks in one place:

The table shows the heart of the change: in the past the cask was a result of the wine trade, today it is a deliberately produced tool for the whisky industry.

Paxarette - the banned additive

In the history of sherry casks there is also a darker chapter: paxarette. It is a thick, sweet concentrate based on sherry - a blend of oloroso, PX and must, sometimes further fortified - with which casks, and even whisky, were once treated. When a cask seemed too tired or whisky too pale, paxarette was added, sometimes literally by the cupful, and in extreme cases forced into the wood under pressure. It gave a quick injection of colour and sweetness, mimicking the effect of real seasoning. In 1990 a revision of the Scotch Whisky rules deemed paxarette an additive affecting flavour and banned it. Today Scotch whisky may not contain it. It is a curious trace of an era when the character of sherry was sometimes faked by shortcut, instead of being patiently drawn from the oak.

Why it matters for the flavour

The way a cask is made really affects the whisky. A cask after long, real seasoning gives the full, deep profile of sherry - dark fruit, nuts, spice, chocolate. But shortly seasoned casks or those from cheap, hasty wine give a shallower and more one-dimensional effect, sometimes with an unpleasant sulphury-rubbery note. This is why not every sherry whisky is equally good - the quality of the oak, the type of wine and the time of seasoning all count. The best producers order casks seasoned long and with good sherry, which costs, but gives class. Understanding that behind the word sherry stands a whole process of varying quality helps you choose bottles deliberately and not overpay for marketing alone.

How to sense it in the glass

You will recognise a good sherry whisky by its rich, dark profile. You sense dried fruit - raisins, figs, dates - plus nuts, dark chocolate, orange peel and warm spice. PX adds thick sweetness and notes of molasses, oloroso a more nutty-spicy backbone. Sometimes a characteristic note of sulphur, gunpowder or rubber appears - in a small dose it adds character, in a large one it betrays a poorer cask. Whisky from a truly good sherry cask has depth and smoothness, not just a sweet, flat colour. It is worth comparing a young bourbon-cask whisky and its sister sherry version, to feel how much a seasoned cask brings. Over time you will start to tell whisky from deep oloroso from one lightly brushed with wine.

The essentials in brief

Let us gather it up. Most of today’s sherry casks did not hold drinking sherry but are made in the seasoning process: new oak is deliberately filled with wine for usually one to two years, to soak the wood, after which the wine is poured out and distilled to brandy or turned into vinegar. This model replaced the old transport casks, which vanished after the Spanish rules of the 1980s requiring sherry to be bottled on the spot. Seasoning mainly uses oloroso and PX, and the type of wine shapes the profile of the whisky. The old paxarette, that is the adding of a sweet concentrate, was banned in 1990. The quality and time of seasoning really decide the flavour. Now you know how sherry casks are really made and why not every sherry whisky is the same.

Note every whisky in GustoNote - including the type of cask and the sherry notes you sense. Over time you will start to recognise deep oloroso and sweet PX, and better understand where the richness of sherry whisky comes from.