How Aging Whisky In Sherry Casks Changed In The Modern Era

Sherry casks today: tailor-made seasoned casks

Virtually all of the current-day ‘sherry casks’ that go into the whisky industry are specially seasoned for this purpose. Maturing sherry wines inside them is not an objective whatsoever and the general idea of sherry casks being ‘re-used’ casks or leftover products of the sherry industry is a false one.

This is how it works. Often a whisky distillery has an agreement with a Spanish tonelería, a cooperage which prepares new oak casks for them. They use American white oak (Quercus Alba) or European oak (Quercus Petraea or Quercus Robur). Note that Quercus Robur would originally come from Spain (mainly up North in Galicia) but harvesting is now highly restricted and therefore this type of wood is not generally available, except for Macallan. Highland Park and other Edrington distilleries who have a specific supply chain for Spanish European oak through the Tevasa cooperage. Nowadays most European oak comes from Romania and France.

Distillers are often vague about the provenance of the wood, especially when it comes to European oak. The term Spanish oak cask also seems to be used incorrectly sometimes, even for American oak casks as long as they were processed and seasoned in a Spanish cooperage.

When a new oak cask is prepared it will be sent to a sherry bodega to be filled with wine, a process called envinado in Spanish. Distilleries can choose from a range of parameters for the wood, the toasting levels, the age and type of wine that goes in, even the way of storage (upright or lying down). The wine stays in for a period roughly between six months and two and a half years. Eighteen months seems to be an industry standard.

When the seasoning is finished, the wine is taken out and often re-used. After a few seasoning runs it will be discarded. The wine can’t legally be sold as sherry and it’s not suited for consumption anyway. Usually it will be distilled into sherry brandy or used to produce sherry vinegar. Unsurprisingly perhaps, one of the largest producers of sherry casks (Páez Lobato) is also the largest producer of sherry vinegar (Páez Morilla).

The role of the wine inside the cask is mostly to round off the edges. It modifies the flavour compounds of the oak, removing the elements that are considered detrimental for whisky maturation: harsh tannins, bitter notes and sulphury off-notes from the freshly toasted wood. At the same time the wood is impregnated with about a dozen litres of the wine. On top of the wine in the pores, producers will leave about 5-10 litres of sherry in the cask to prevent it from drying out during transport to Scotland. Most distilleries will tell you this is poured out before the whisky goes in, as anything not taken up by the wood is considered an additive.

Sherry seasoning is now a fairly big business. Most of the larger sherry bodegas in the area are active in preparing casks for the whisky industry: Lustau, Williams & Humbert, Fernando de Castilla, Hidalgo La Gitana… often in partnerships with cooperages like Tevasa, Paez Lobato, Vasyma, Huberto Domecq or Tonelería del Sur. However, we should keep in mind that the production of sherry and the production of sherry casks for the whisky industry are two separate businesses with fewer common grounds than most whisky lovers think. You often hear people say drink more sherry, it will help to get more sherry matured whisky. Well, maybe not entirely.