TLDR

What are sherry casks?

Sherry casks also known as botas or barrels are a crucial part of the Solera Sherry ageing process. These are not to be confused with the Sherry casks used by the whisky industry. Sherry casks used for whisky maturation made prior to 1981 were transport casks which held Sherry for its journey to Britain. Since this time the industry has relied upon specially seasoned casks created specifically for the whisky industry.

The Long Read

What is the Solera method?

The Solera method is a process of aging liquids such as wine, rum and brandy, by fractional blending so that the finished product is a mixture of ages. In this system, the casks are stacked on top of another, to allow the transfer cascade. That is, the change of liquids from one barrel to another by gravity.

One of the characteristics of this system is that the percentage of the content of the barrels that is removed to fill others is limited. Legally in Spain the barrels can only be emptied by one third at a time. The cask is never completely emptied and so every subsequent bottling will contain a percentage of the oldest spirit. When the liquid assigned to the oldest barrels has been removed, it is refilled with wine from the next oldest barrel and this continues along the solera line.

What is a Solera cask?

Solera casks are the casks used within the solera system of fractional blending for Sherry, run and other spirits. Solera barrels are of inestimable valuable, and are only removed from the system if they are damaged.

How are whisky sherry casks different from solera casks?

Sherry casks used by the whisky industry were historically casks used transport sherry to the docks of Scotland and other parts of Britain, today they are specially seasoned casks. The two types could never be compared, because the barrels used within the Solera system have likely contained sherry for anything up to and over 100 years, whisky casks are unlikely to have held liquid for more than 2 years.

Even if the whisky industry was willing to pay the price for casks containing VORS (“Very Old Rare Sherry”) there simply isn’t enough casks in the world to provide the needs of the whisky industry.

The Truth about whisky sherry casks

While manufacturers like to present it differently essentially no sherry casks in Scottish warehouses are real bodega casks that have been used for sherry maturation. Sherry Bodegas use their casks until virtual exhaustion, and even were this not the cast are not numerous enough to supply sufficient volumes for whisky maturation. This is not a new development, and it was almost never the case that Bodega casks were used.

Historically, before the introduction of bottling in bond, sherries were exported from Spain to Great Britain by sea in oak casks. Rather than transporting these now empty casks back to Spain for reuse these casks were sold on once emptied, and thus these barrels ended up in Scotland and were used for the maturation of whisky. These transport casks were still extremely flavourable having held the sherry for prolonged periods of time, firstly while waiting in warehouses, then during long shipping times, then in warehouses at the other end until they were finally emptied. Today significantly less sherry is consumed within the UK, and the end of shipping in casks has meant that these ‘transport’ casks are no longer readily available.

In the absence of these transport casks the whisky industry predominantly shifted production to the use of ex-bourbon casks which are plentiful due to legal restrictions allowing them to be used only once for bourbon maturation. The remaining sherry matured whiskies are actually ‘seasoned casks’, produced specially for Scottish distilleries at the Spanish bodegas. Whiskies maturing in ‘Oloroso sherry casks’ are in reality whiskies matured in a cask that previously held a sherry like wine. Despite this the industry will continue to refer to these as sherry casks, for now.

Seasoned ‘Sherry’ casks

In order to satisfy the whiskey industry’s great need for sherry casks, “artificial” sherry casks are now being produced. For this purpose, barrels are filled with sherry for at least twelve months, but potentially as long as thirty, which only serves the sole purpose of turning a barrel into a sherry barrel. The sherry is then no longer sold as a drink, but after it has been used several times to condition barrels into sherry barrels, it is used to make vinegar. This process is called “Seasoning” and was described in an article by TheDrinksReport in 2015

After the desired time has elapsed, the wine is usually removed and reused in another barrel. While this may not be as romantic as some would have you believe, but it does mean that distilleries can use custom seasoned casks to obtain the specific characteristics they desire.

It’s also true that as the transport casks were not the Solera casks used to mature the sherry. As a result, the barrels only came into contact with sherry for a relatively short period of time and were therefore probably not dissimilar in their texture (with the exception of the type of wood) to the barrels, which are made into sherry barrels by seasoning.

Why is whisky matured in sherry casks?

Whisky has been matured in Sherry casks for two reasons:

• Scotland lacks sufficient national forests to produce casks
• Sherry casks are prized for their flavour enhancing properties

Ship and barrel creation

The timber used for shipbuilding is identical to that of cask production. It is estimated that in the 18th Century, a 110-gun ship required the felling of 4,000 oak trees, the equivalent of 30–40 hectares of woodland. By 1790, the Royal Navy had about 300 ships in its ranks. To build this navy, at least 1,200,000 good oaks must have been cut. While other European powers such as Spain practiced careful wood management much of Britain was largely deforested. Even after demand for shipbuilding declined forest management has been continued for cask management.

The growth of the trees is a very slow process, as well as the drying of the staves, once cut, either in the open air or by means of an oven. John Niehoff, who is in charge of the cask management at Brown-Forman, estimates that it takes about 70 years for the oaks to be ready to be cut, and that the drying and building process of the barrel takes another 9 months. European oaks take a little longer to grow and as drying in the open air is more common this stage generally takes longer.

Sherry transport casks were initially used because making new oak barrels in Scotland was simply not an option. Fortunately casks that had already been used to transport sherry, wine, and rum were readily available on docks across the country.

Flavour creation

When Sherry, or a sherry like wine, is in an oak cask, it interacts with the wood and changes its compounds. Once emptied and refilled with whisky these compounds interact with the whisky, imparting the taste characteristics of the barrel, and creating new flavour compounds.

Characteristics of the Jerez wine barrel

Many whisky fans prize sherry cask whiskiess because the sherry cask strips bitter, harsher tannins creating the the rich spice notes and the characteristic “Christmas cake” of fruit and spice. However, different types of sherry produce different characteristics in whisky including:

• Fino: Nuts, fresh, citrus
• Manzanilla : Very similar to Fino oak barrels but with a certain salty and marine flavor due to the region where Manzanilla is produced.
• Oloroso : These barrels give the whisky the most powerful and rich characteristics associated with a sherry cask whisky such as Christmas cake, hot spices and dried fruit.
• Pedro Ximénez : A barrel of PX sherry will give a whisky intense sweetness because sherry grapes are dried in the sun, which releases a large amount of sugar. You’ll also get the dark and rich flavors of chocolate and espresso from these whiskies.

Influence of wood type on flavour

While previous filling is the major contributing factor to taste the wood used for barrel creation is also important. American oak has a broad grain that gives rise to a large number of sweet flavors (vanilla, fresh fruit). European oak is tight-grained, giving it a darker, spicier flavor, like that of dried fruit.

Cask reuse and flavour

With the exception of bourbon, which legally requires the use of new barrels, whisky makers around the world often choose to reuse their barrels for second or even third fills. In this way, the intensity of the contributions decreases progressively, but they save on expenses. The consumer is often informed via the whisky labels which treat these uses as first fill, second fill etc. Historically Paxarette was used to reseason casks, however this practice has since been banned.