Whisky in Oloroso Sherry casks

1. The Origin

The Oloroso sherry has its origins in the south west of Spain. It is a fortified wine with 17-22% ABV and a sugar content of 0-5 grams per liter. With these stats the Oloroso is defined as a dry wine. But many of the Sherry blenders sweeten the wine to make it more luscious and syrup like. Within the wine connoisseurs the Oloroso is handled as a very nutty sherry with dark flavours.

A warehouse of sherry in southern Spain
A warehouse in Jerez, Southern Spain

2. Production and post treatment

Sherry is matured in oak casks. The ages differ from no age sherries up to 30 years of age. The wood used in the barrels is quercus alba, the American Oak. Oloroso is not a natural product by fermentation. After the alcoholic fermentation the sherry undergoes fortification (adding grape spirit aka Brandy). The ABV has to be raised above 17% for Oloroso. This prevents the rest of the dead yeast to produce the protective layer of flor (A white layer on top of the sherry in the cask).  This results in an oxidative maturation of the Sherry. Many of the Sherry bands are matured in the Solera maturation process in which the content of several casks is mixed together in Solera vats. After a marrying period of several month part of the batch is filled into bottles. The missing Sherry in the Solery vat is replaced by fresh Sherry and the mixing starts anew. 

Maturing sherry cask with flor
Sherry cask with flor (yeast layer)
Maturing sherry cask
Oloroso Sherry cask without flor (yeast layer)

3. Effect on the Taste

Whiskies matured in Oloroso casks are usually taking up the dark flavours and the nuttiness. The dark flavours manifest in taste of figs, raisins, and many more fruits. Most of the whisky connoisseurs also find the Oloroso matured whiskies more oily and smooth than other whiskies. 

A lid of a sherry cask labeled with Glenfarclas
Sherry cask at the Glenfarclas distillery

4. Effect on the Colour

The Oloroso is very dark after the normal fermentation and maturation. This usually results in a darker colour and is very favorable for the whisky. 

However the dark colour of the sherry is not always favourable in the sherry business. The brand Bristol Cream is said to lighten its sherry by putting it through a charcoal filter. This process is also done by the Jack Daniels Distillery. But JD filters its spirit before the maturation to mellow the spirit and not touch the dark colour.

5. Whisky Examples

Most of the whiskies are only finished in Oloroso sherry casks. There are just a handful of whiskies that are fully matured in these casks. Whiskies that are matured in Oloroso sherry casks for more than 10 years are usually very intense and remind more of a liqueur than a whisky. 

Glenfarclas 1993 Oloroso Sherry Cask

A very sherry sided whisky that has been matured in Oloroso sherry casks. It is very dark for an uncoloured whisky. You taste a very sweet whisky that reminds you of christmas.

Dalwhinnie Distillers Edition

This Dalwhinne was finished in Oloroso sherry casks. It is just as dark as the Glenfarclas, but this comes from the colour that was added. However this time the dark fruits are combined with some peat smoke and also the oak tones come through.

 

Aberlour 18 years old

The 18 years is one of the whiskies that has a light distillery character and the addition of the Oloroso character makes the whisky very liqueur like. 

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