Cask Maturation at Kilchoman

Each part of the production process at Kilchoman has an influence in creating the final liquid we fill into our bottles. One of the last processes before bottling – and the process which takes the longest time – is the maturation. At Kilchoman we’re proud to say that we warehouse 100% of our spirit on Islay, right here at the distillery.

To produce Single Malt Whisky, the legal requirement is a minimum maturation period of 3 years and 1 day, matured within oak barrels. These oak barrels come in a variety of styles, shapes and sizes and we’re going to go through some of the main varieties we use here at Kilchoman.

Once our spirit stills produce the heart of the distillation at approximately 70%ABV, this is reduced to 63.5%ABV with water from Glen Osamail burn before filling into our hand-picked casks.

Kilchoman spirit is predominately matured in Bourbon casks – a decision made by founder and Managing Director, Anthony Wills.  Bourbon casks are the most widely used casks within the Single Malt industry. They are shipped to Scotland directly after being used only once due to the long-standing legislation in America.  Flavour profiles that can be found from Bourbon matured Kilchoman releases can range from butterscotch and honey to vanilla. Bourbon casks are 200L in capacity, constructed using American white oak (Quercus Alba). Kilchoman Machir Bay – our award-winning core whisky – is created using close to 90% Bourbon matured spirit which allows the unique style of Kilchoman to come through with ease.

Sherry casks are our second most used for maturation at Kilchoman. We directly source each variety of sherry cask from Bodega Miguel Martin in Spain; Oloroso, Pedro Ximénez (PX) and Fino. These casks can be in the form of Hogsheads (approx. 225-250 litres) or Butts (approx. 475-500 litres). Each variety of sherry will impart its own unique flavour and aroma onto the Kilchoman spirit throughout maturation. Using Oloroso, Anthony would expect to find flavours such as dried fruits and spice alongside nutty aromas. Alternatively, using PX provides us with a sweeter sherried profile and will give added influence in dark chocolate, dates, figs, and honey. Fino offers a drier, more saline type of sherry which allows for a profile dominated by green fruits.

Cask experimentation will always play a vital role at Kilchoman and since the first cask filled in 2005, we have experimented with many varieties, some of which are Madeira, Port, and Red Wine. Our progression in cask experimentation grows as the Scotch Whisky Association (SWA) continues to ease restrictions on the variety of casks available to use for maturation. In 2019, the SWA opened the category further, allowing distilleries access to additional varieties of casks – if cask maturation is part of the traditional production process of these spirits – for example, Tequila, Mezcal and Calvados. Anthony used this is an opportunity to fill 25 Tequila and 25 Mezcal casks with some intended for finishing and some for a full maturation.

Once Anthony has chosen the cask for maturation, the casks are filled and taken to our on-site warehouses.  Two styles of maturation are used at Kilchoman, dunnage and racking. Our traditional dunnage warehouses are stowed 3 high on top of earth floors. Our newly built racked warehouses are designed to stow 10 high on steel frames. Over the maturation period, we expect to see anywhere between 1.5-2% volume loss per year, otherwise known as the ‘angel’s share’.

The colour of Single Malt is often discussed during tastings. When producing Single Malt Whisky, the addition of caramel colouring (E150a) is legally authorised. If E150a is added, it can turn a lightly coloured whisky, dark. The additive acts as a modifier correcting any natural variations that may be present.  It’s worth noting, E150a doesn’t affect the flavour profile but allows for uniformity, ensuring that each release is visually identical. At Kilchoman it’s important that we release natural whisky, free from additives. This means that all the colour comes exclusively from the cask. We would expect our Bourbon casks to give a golden or caramel colour to the Kilchoman spirit. Sherry casks will provide a darker, deeper finish. This means that each release may vary in colour slightly, which is the beauty of creating a natural Single Malt and something that we celebrate here at Kilchoman.

Each cask will be used for maturing Kilchoman spirit only twice. After the second use, our casks will be sold and will continue their life in the wider whisky industry. This is to ensure we have the maximum amount of flavour from the oak imparted into our whisky. It’s a common misconception that Single Malt Whisky must have significant age to be considered a great whisky, but Kilchoman demonstrates otherwise. The distillery was designed to release a ‘younger’ style of Islay Single Malt; a fine balance between producing an elegant Islay spirit, coupled with selecting the correct cask for maturation has shown quality and depth of flavour.

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