Accelerating whisky maturation

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The whisky shimmers a deep golden hue in the glass, its scent promises complex and delicate aromas but upon taking the first sip you’re left with only disappointment. The single malt tastes narrow, has no depth and somehow seems young. While it is always possible for a whisky to simply have a nose which surpasses the palate it is also possible that your whisky is the result of tricks and techniques to accelerate the perceived maturation and prettify their young distillates.

A whisky gets a large part of its aromas (some credit as much as 80%) from the oak barrels in which it is stored and matured. These were previously often pre-filled bourbon casks, wine, Oloroso or other sherry casks. Many producers only use one style of cask, while others age their whisky in two or three styles.

Multiple casks maturation

Resourceful whisky makers use significantly more different casks with the most diverse pre-filled casks. In this way, more aromas quickly come into young single malt and these flavour dominant casks can be blended to create the impression of complexity. Or as an alternative the liquid can be moved through a series of casks, each subsequent cask being used to mask poor quality or unpleasant notes from previous casks

The problem with this is simple enough, the short maturation in many different casks gives the whisky mainly superficial aromas, but no real maturity or depth. Beginners in particular are quickly impressed by the large selection of casks on paper and the potpourri of flavors in their mouths. Unfortunately when taking a closer look, you will quickly notice that the aromas appear relatively flat and “ironed over”. After the first level there is often not much. At the same time, many multiple-casks whiskies appear simply over rounded, or overloaded in their composition - as in almost all things, less can be more, and quality is needed over quantity when selecting casks for maturation.

Virgin oak maturation

New (never used) oak casks are also known as virgin oak casks. They have traditionally been used sparingly in the Scottish whisky industry. This is because these casks bring very intense oak notes to the whisky as well as dominant notes of vanilla & toffee. However if a single malt is stored in these casks for even a few years sharp, woody notes tend to develop.

If you fill a freshly distilled whisky in virgin oak casks, maturity can be simulated quickly. After just three years, the distillate has a clearly recognizable oak note. Even boring older whiskies from the warehouse can be “spiced up” in the new casks and provided with additional wood aromas.

The fleeting connoisseur tastes the intensive oak wood notes and combines them with a long barrel aging. Unfortunately if you taste it attentively, you will quickly notice that there are only a few other aromas waiting behind the concise note of wood. The fresh oak wood dominates the taste and leaves little room for other notes. In fact, of course, there are also good Virgin Oak whiskies. With young whiskies, however, the wood aromas often deliberately mask the immature age of the single malt. If an old whisky suddenly gets a finish in virgin oak casks after many years in the cask, then caution is often required.

Sherry cask maturation

Sherry casks have a reputation for bringing particularly complex aromas to Scotch whisky. We immediately have the image of ancient bodega casks in our minds, just waiting in the dim light of old vaults in Spain for a Scottish whisky maker to pick them up and fill them with the finest single malt.

In reality these casks are rather sherry-esque seasoned casks, which are manufactured according to specifications from the whisky distilleries. These casks filled with fresh sherry like product and are stored in huge high-bay warehouses. After the alloted time usually a few months - they have been flavored with the sherry notes recognizable to whisky fans. What many connoisseurs don’t know: up to 10 liters of sherry are still in the barrel when delivered to Scotland, and another 20 liters are in the barrel walls. With a 250 liter sherry hogshead, that’s quite a proportion, which will quickly characterize the aroma of the whisky.

With a finish in sherry casks, strong fruit aromas can be brought into a whisky in a short time. With the storage in the Spanish barrels, even boring malts can be beautified quickly. Single malts that are fully matured in sherry casks over many years often outperform these finished whiskies. While oloroso or PX casks also impart strong dark colour to th whisky further enhancing the percieved age it’s worth noting that sherry seasoned casks do not bring the same aromatic depth and variety to a whisky as full maturation in these casks.

The colour trick

A whisky with a strong colour automatically appears more mature. The distilleries can legally help out here and colour their whiskies with the food colouring caramel (E150). Officially, it is often said that consistency of colour across many bottles is important and that one does not want to confuse the buyer.

Especially with younger whiskies, the colour is helped with significantly more caramel (E150) than necessary. And so the no-age statements in the portfolio of many well-known distilleries are sometimes the whiskies with the darkest tint.

The assessment of the whisky colour is led ad absurdum by the addition of caramel. Since the re-dyeing is only for cosmetic and sales-related reasons, it could actually be omitted with the natural product whisky. Unfortunately, as long as natural whiskies do not sell much better than their coloured counterparts, this will probably not change any time soon.

Tips & considerations

While only the last of the techniques used above can truly be called manipulative it’s worth considering a few factors when buying whisky:

  • Age
  • ABV & Colour
  • Numer of casks used
  • Type of cask maturation

The age of a whisky

A high age statement is not a reliable guarantee for a great whisky - but in combination with a serious cask selection it is an important and useful indicator. The chance of trying any whisky with an age statement and going bust is generally lower than trying the same thing with a whisky without an age statement.

ABV & Colour

While colour is a dangerous measure given the use of spirit caramel these two factors in combination can be useful. A whisky bottled without caramel colouring but with a deep and dark hue has likely aquired a lot of wood influence. Likewise one with an ABV above 43%-46% has almost certainly not undergone chill filtration. While you can get very bad bottles released without either process, and great ones released which have undergone both the ratio stacks clearly one way. Chill filtration strips mouthfeel, and spirit caramel is often used to trick the senses.

The number of casks used for maturation

The choice of casks must match the whisky. If a young whisky matures in many different casks, caution is often required. Here one should question what influence four or more casks can have on the whisky in such a short time. Less is often more here. That is not to say that a double, or even triple wood whisky is of low quality - this may well be done with a vast number of casks to create a signature style. However if this has been done to a so called single cask whisky, or a whisky being sold as part of a limited run of bottles then caution should be paid.

Type & quality of casks

The newer a cask, the more intense the flavors it brings to the whisky. This is not to say the older casks are always inferior, if anything its the opinion of this author that casks tend to peak towards the middle of their lives*. However the better your understanding of the casks use the better you can predict the taste of the final product. Beyond previous content casks are often recorded as:

  • First-fill casks are filled with single malt whisky for the first time after they have been pre-filled (e.g. with bourbon or sherry) and bring a particularly large number of aromas to the whisky
  • Second-fill casks are filled with a single malt for the second time, the intensity is already lower here
  • Refill-Casks are used three times, four times or more. Even after recharring of casks in a process similar to STR casks, these barrels bring significantly fewer aromas into the whisky and maturation can take far longer.

*Virgin casks impart little more than vanilla and toffee when first used and quickly overpower many spirits. Newly seasoned sherry casks can likewise be overly dominant, and rejuvenated casks tend to be inferior to virgin oak but still toffee and vanilla dominant.

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