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Cask Maturations and Cask Finishes

The process of maturation of whisky on oak casks has the single greatest influence on the character, flavour and aroma of the spirit. Watch a video from Glengoyne

The whisky is influenced in two ways:

  1. The type of oak from which the cask is made and its treatment
  2. The previous occupant of the cask, (if any)

cask maturation

The influence of the oak

European Oak (Also known as English, French or Scottish oak) - Quercus Robur (Red Oak)

  • Takes around 100 years to reach full height
  • The structure of the stave is generally more knotty with a coarser grain which allows a slightly faster maturation.
  • The higher tannin levels of Quercus Robur contribute flavours of nuttiness, stone fruit, apple and spice, notably nutmeg.
  • Traditional original occupants include sherry and port etc.

Note: England boasts the oldest oaks in Europe and the average lifespan is 700 - 1200 years

American Oak - Quercus Alba (White Oak)

  • Matures in around 20 years 
  • The wood has a finer grain resulting in a slower maturation
  • Produces creamy flavours, notably vanilla, coconut, banana and spice
  • Traditional previous occupant is Bourbon

Note: Oldest documented Quercus Alba is 450 years

The treatment of oak

Oak casks used for maturing whisky have typically been toasted over fire.The charcoal produced helps filter impurities from the whisky and adds both colour and flavour to the whisky

Toasting American oak produces woody, vanilla and coconut flavours

Toasting European oak produces flavours of vanilla and coffee.

The influence of the previous occupant

The following notes are generalised. Perceived flavours vary from whisky to whisky and from palate to palate.

Sherry.

Different types of sherry will produce different flavours. Here are some examples:

Dry Olorosso (Favoured by macallan and Glenfarclas)

Produces dark flavours of figs and raisins and a certain nuttiness and a dark colour

Pedro Ximenez (PX) is a dark sweet sherry (Vintage lagavulin), 

Flavours of syrupy dried fruits and raisins with a dark brownish colour

Amontillado Sherry. Has been used by Laphroaig and Glenkinchie in special editions. Amontillado adds an amber hue to the colour of whisky.

Fresh acidity, nutty, dry and sweet

Manzanilla sherry (A type of Fino) (Not regularly used by any distillery)

This is a dry almost clear sherry that adds negligible colour and a certain acidic dryness to whisky. It is sometimes associated with saltiness.

Other Fino sherries may add a floral note.

Bourbon

Most Glenmorangie and Ardbeg is matured on ex-bourbon casks.

Many Scotch whiskies are now being matured on ex-Bourbon casks as the supply of sherry casks dries up. Bourbon has to be matured on a virgin cask, which then becomes redundant after the process is completed.

Flavour: Whisky matured on ex Bourbon typically has vanilla from the American Oak used, sweetness from the high corn content of Bourbon and spiciness from the rye.

Colour: Golden

Port

Adds a reddish hue to the whisky. Common flavours are spicy with dried fruits and sweetness reflected by the sweetness of the original port. 

Wine

Sauternes - Very successfully used as a finish by Arran and Glenmorangie in their Nectar D'or

Contributes a bright amber glow and sweet, zesty acidity with light fruitness

Burgundy and other red wine 

Can add dryness or sweetness and an intense fruity flavour, with a dark red colour. 

Has been used with varying degrees of success but worked particularly well for the New Zealand whisky company when used in their double wood blend.