Re-using casks is pragmatic but also a creative opportunity. Each ‘fill’ (ie. each time a cask is used) has a different influence on the maturing whisky, and provides another expression of the house style. In theory, each cask has the same potential, but how it is utilised during a typical life-cycle of 20-30 years isn’t predetermined. Whether this is, for example, three fills of 10 years each, or one longer fill, is decided during the ageing process.
“Every cask could end up in any number of expressions. An on-going program of assessing samples drawn from casks provides us with knowledge of the cask’s influence, and we usually sample whiskies at three years, and at six to eight years, to help us decide how these whiskies will be used. When casks are emptied to bottle the contents, we assess each cask’s potential for another fill,” says Brian Kinsman, master blender, William Grant.
An on-going program of assessing samples drawn from casks provides us with knowledge of the cask’s influence, and we usually sample whiskies at three years, and at six to eight years, to help us decide how these whiskies will be used
Samples are usually sent from the warehouse to the lab, where first impres-sions are purely visual. “The colour of the whisky gives a good indication of how well a cask is performing. For example, a 10-years-old whisky from a first fill Bourbon should have a pale gold to light brown colour. A 10-years-old whisky from a first fill sherry cask is deep red to amber. A lack of colour shows something is wrong,” says Allan Logan, Bruichladdich’s production director.
The next step is nosing, which is the principal method rather than tasting.
“When nosing I’m looking for the ideal profile for the age of the whisky and the type of cask. This means knowing how individual malts from our distilleries should show in a first fill, second fill, third fill, American oak and Spanish oak. You can only learn all these parameters by nosing a lot of casks and knowing what to look for. It’s totally about experience. After assessing the first 100,000 casks I gave up counting,” says Stuart Harvey, master blender, Inver House Distillers.
So, what does this mean for individual cask types?
“After 10 years in a first fill Spanish oak cask I’m looking for a specific level of spice, raisins, chocolate and Christmas cake aromas and flavours. After 10 years in a first fill American oak Bourbon barrel I’m looking for vanilla, oak and toffee,” adds Harvey.
Clearly, a key aspect of this process is the performance level of casks.
“When casks start getting tired the aromas become more spirity, rather than fresh oak, and any off notes, such as sulphur, sound alarm bells"
“Typically 90 per cent of the casks show a uniform level of oak influence, with about five per cent being more intense and five per cent less intense. However, ‘more intense’ and ‘less intense’ are relative terms, as we’re looking at the level of cask influence effectively under a microscope,” says Brendan McCarron, head of maturing whisky stocks, Glenmorangie.
The rate of first fill Bourbon and Sherry casks providing a second fill is essentially (though not entirely) 100 per cent.
“Second fill to third fill has similarly high rates of success as first to second fill, and third fill has its value as a less active oak influence results in more distillery character from the new make spirit showing through. This means, for example, that a third fill cask preserves more of the smoke in Ardbeg,” says Brendan McCarron.
Meanwhile, the assessment process also includes checking aromas that emanate from within the cask. “When casks start getting tired the aromas become more spirity, rather than fresh oak, and any off notes, such as sulphur, sound alarm bells." says Logan.
So, why do casks have varying life-cycles and performance levels? One answer lies in the ageing warehouses.
“Different warehouses have a different impact on the rate of maturation, as do various locations in the same warehouse. In our tallest warehouse the casks at the top are at a height of 14 metres, with the lowest casks on the ground floor. On one day last May there was a difference in temperature of 19 degrees centigrade between the floor and the casks at the top of the ware-house,” says Logan.
The importance of record keeping
Knowing the provenance of each cask is of course vital, and all the data is only a ‘click’ away.
“On the head of each cask we staple a small plastic label with a barcode that can be scanned using a hand-held device. This uploads information onto a screen or laptop that enables you to check the cask provenance, such as the species of oak, the bodega it originated from, and when the cask was filled at the distillery,” says Stuart MacPherson, Macallan’s master of wood.
This high-tech approach is a more recent innovation, with the traditional system being to stencil a code onto the head of each cask (conveying some key cask facts), which in turn corresponds to a hand-written entry in a leather-bound ledger. However, a number of distilleries use both methods. Stenciling makes it easier to identify casks from a distance, while bar codes facilitate a more detailed follow up.