CASK TYPES
CHARGON
When browsing the Society’s latest Outturn, it’s easy to get lost in the jargon used to describe our wide variety of casks. Join Ed Furmston-Evans as he uncovers the meaning behind the Society’s lesser-known cask types
PHOTOS: PETER SANDGROUND
HEAVY TOAST MEDIUM CHAR
Having been pioneered by the Society’s own head of whisky creation, Euan Campbell, heavy toast medium char casks (HTMC) have featured regularly in Outturns over the past ten years. But to really understand what HTMC actually is, it first helps to have a little background on the process of cask construction. When casks are crafted in the cooperage, after first shaping the wood and ‘raising’ it into the traditional shape, the cooper must then heat treat the inside of the cask. Beyond adding heat to help bend the staves, this is important for two reasons. Firstly, heat treatment opens the pores of the wood, allowing the spirit to flow in and out and pulling out flavour compounds. Secondly, it breaks down the large molecules that make up the structure of the wood into flavour active compounds that will introduce character and depth to the whisky.
There are two main types of heat treatment: toasting and charring. Toasting is a longer process where casks are heated by a small fire at a relatively low temperature for a long time. Here the cooper can carefully control the fire to achieve the desired temperature and flavour profile.
This can include things like adding more wood, splashing it with water and controlling the airflow. Toasting breaks down the tannins, lignin and hemicellulose structures in the wood to create flavour active compounds and is the process traditionally used for sherry, wine and brandy casks.
Charring is a much faster and hotter heat-treatment process where the wood is allowed to catch on fire. The cooper watches the temperature and after a set period, usually around 60 seconds for a heavy char, quenches the fire with water. This process creates a layer of charcoal which filters out feinty character from spirit, while toasting the wood behind the charred layer creates extractable compounds for additional flavour. It’s a legal requirement that bourbon is matured in new charred oak casks.
Charring and toasting both have their own benefits, and each has a unique impact on the whisky. By first slowly toasting the barrel for 30 minutes before charring it for 60 seconds, the HTMC process combines both these influences within the same cask. The result is a cask that develops flavours of rich vanilla custard, buttery pastry and red fruits, wrapped up in unctuous creamy mouthfeel.
SHAVED, TOASTED AND RE-CHARRED
This is a rejuvenation technique, used to give new life to older casks. Shaved, toasted and re-charred casks (STR) are ex-red wine casks where the top three millimetres of wood from the inside of the cask is removed, exposing fresh wood unpenetrated by the wine.
The casks are then toasted before a fresh layer of char is added, giving them a new lease of life. This process was introduced to the whisky industry by legendary whisky scientist, blender and master distiller Jim Swan. His impact on the industry was clear, with many of the distilleries he helped establish still using this treatment today.
The flavour impact of STR casks will depend on the level of toasting applied, but we would likely expect notes of vanilla, caramel and fresh brioche to come through. Depending on the level of tannins in each oak species, notes of baking spices might accompany the red fruit infusion left by the wine.
RE-CHARRED
Another common form of rejuvenated casks is re-charred or de-char re-char casks, which are ex-bourbon casks close to exhaustion. By scraping off the original layer of char in the cask, the cooper can then treat these casks with additional grilling, adding a new layer of char.
Because these casks have generally been used for spirit multiple times, there is less opportunity to refresh the extractives from the wood. Instead, the main goal is to clean up immature spirit character and give more of a subtle cask influence.
This can be very helpful in cases where we really want the character of the distillate to shine through in the eventual bottling. We can also help increase the impact of these casks by adding virgin oak heads. This makes up 30 per cent of the cask’s surface area and can have a significant influence on the whisky.
ABOVE: Exposing the staves to high temperatures helps develop new flavours