What is an Oloroso Sherry Cask?

Oloroso Sherry Cask are whisky casks which have been previously held Oloroso Sherry. Oloroso Sherry is a type of fortified wine produced near the city of Jerez de la Frontera in Andalusia, Spain. The Sherry Triangle produces wines which have been ‘fortified’ with a higher alcohol strength in order to prevent yeast growth and bottled under the official name of Jerez-Xérès-Sherry. There is something of a manufactured misconception, that the casks used at these bodegas are the same used for whisky maturation however this is not the case. Oloroso sherry casks are more commonly known as sherry butts within the whisky industry.

The Truth about 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 for our purposes we will continue to refer to these as Oloroso sherry casks.

What is Oloroso Sherry?

Sherry is generally fortified white wines. Oloroso is an oxidatively ripened sherry made from palomino grapes. This type of sherry is typically full-bodied, strong and dry, but is sometimes sweetened by adding other types of sherry. The properties of Oloroso sherry are transferred to the barrel and later on to the whisky.

Where do Oloroso sherry barrels come from?

Oloroso sherry barrels always come from Spain. More precisely from the area around the town of Jerez de la Frontera in the south of the Iberian Peninsula. The different sherry wines may only be produced in the so-called “sherry triangle”.

Why is whisky aged in Oloroso barrels?

Because of their harmonious character, Oloroso casks are very popular for maturing whisky. The taste of the Oloroso sherry fits in elegantly with the aromas of the whisky in most of the bottlings, but is not too dominant. In this way, Oloroso sherry barrels can add more aromas to a bottling. Oak barrels of other types of sherry, such as Pedro Ximénez (PX), are also used to mature whisky. However, Oloroso barrels are less sweet and luscious compared to PX casks.

There are several variants for storage:

  • A sherry cask whisky is stored in sherry barrels for its entire duration
  • A single malt with a sherry finish often matures initially in ex-bourbon barrels and then completely in a sherry cask (e.g. Oloroso cask) for a few months / years
  • During parallel maturation , part of the whisky is stored in ex-bourbon barrels, another in, for example, Oloroso sherry casks. Then there is a marriage of both types.

What flavours does the Oloroso sherry bring to the whisky?

Oloroso sherries are dry, strong and full-bodied in their character. Whiskies that were matured in former Oloroso sherry casks are mostly characterized by woody and ripe, fruity aromas. The respective aroma profile also depends on the duration of maturation, the intensity (first fill, second fill) and the quality of the barrels used.

Typical for whisky matured in Oloroso casks is a dry, but also soft, full mouthfeel. Concise notes that can be discovered in whisky matured in Oloroso casks are dried fruits such as figs, plums and raisins. The fruit notes are often complemented by distinctively spicy oak notes.

How big are Oloroso sherry casks?

With a volume of 500 litres, Oloroso sherry barrels are significantly larger than conventional American Standard Barrels (ASB) ex-bourbon barrels, which have a capacity of only 200 litres, and of the rebuilt hogshead, which hold between 225 to 250 litres. A whisky tends to mature more slowly in larger barrels, as relatively less new make comes into contact with the barrel surface. A complete storage of the whisky in the barrels for many years becomes an option.

However, not all sherry cask whiskies are actually stored in butts. On request, the bodegas also produce sherry hogshead in the desired specification, which can then be placed in Scottish warehouses next to bourbon casks of the same size. For the production of the sherry barrels, European as well as American oak wood can be used. The term ‘matured in spanish oak casks’, which can be found on some whisky bottles, refers to the manufacture of the casks in Spain, but not to the origin of the wood or the type of oak.

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