Origin
Originating in south-western Spain, Oloroso Sherry is a fortified wine with an alcohol content of 17-22% vol. and a sugar content of 0-5 grams per litre, which classifies it as a dry wine. However, sherry is often sweetened to make it juicier and more syrupy. Among wine connoisseurs, Oloroso is considered a very nutty sherry with dark aromas.
Production and post-treatment
Sherry matures in oak barrels, which today are mostly made of the American white oak Quercus alba. The age range extends from sherries with no age indication to 30 years of maturation. Oloroso is not produced by natural fermentation alone. After alcoholic fermentation, the sherry is fortified by adding brandy. The alcohol content must be raised to over 17%, which prevents the yeast from forming a white pile on the sherry in the barrel. Thus, oloroso sherry matures oxidatively. Many sherries are produced using the solera method. Several rows of barrels are stacked on top of each other, with the bottom row containing the oldest sherry. Some of the old casks are now filled and topped up with sherry from the "next younger" cask, which in turn is topped up with sherry from the row above, while new sherry is poured into the top cask.
Effect on the taste
Whisky matured in oloroso sherry casks usually picks up the nuttiness and dark flavours such as those of figs, sultanas and other fruits. Most whisky connoisseurs also find Oloroso-matured whiskies to be oilier and smoother than other whiskies.
Effect on the colour
Oloroso is very dark after maturation. This also leads to a darker colour in the whisky, which is usually welcomed.
In the sherry industry, however, the dark colour is not always intentional. The Bristol Cream brand, for example, is said to lighten its sherry by carbon filtration. Incidentally, this process is also used at Jack Daniel's, where the raw spirit is filtered before maturation, not to lighten it, but to make it softer.
Whisky examples
Most whiskies only receive an oloroso finish. Only a few mature for the full time in such casks. Whiskies that mature for more than ten years in oloroso casks are usually very intense and more reminiscent of a liqueur than of whisky.
