Double Maturation

What is ‘double maturation’? Is it the same as ‘wood finishing’?

Before it can be named ‘whisky’ new-make spirit must be matured for at least three years in oak casks. These play a crucial role in developing colour and flavour in the finished product – some distillers claim that up to 80% of the flavour of a mature whisky derives from the cask, backed up by an old saying: “the wood makes the whisky”. But such a high level of impact depends on how ‘active’ the casks are: virgin casks (rarely used for Scotch whisky, but part of the definition of ‘straight bourbon’ and ‘straight rye’ whiskeys in the U.S.A.) are highly active, refill casks less so, and their activity diminishes the more times they are filled, until they become ‘exhausted’ (after three or four fills). They are then ‘rejuvenated’ by being de-charred and re-charred, or re-purposed as garden furniture.

The majority of the casks maturing Scotch whisky are refills, for the simple reason that distillers – and, more important, blenders - do not want the whisky’s inherent ‘distillery character’ to be swamped by flavours coming from the wood. If the mature whisky is to be bottled as a single malt, some distillers will transfer the liquid into a more active cask for the final months or years of its maturation. This is termed re-racking, and the process as ‘double maturation’ or ‘wood /cask finishing’ – the terms are synonymous, although some would say that the last implies a briefer period in the second cask – months rather than years.

Typically the second cask will have been seasoned with wine – sherry, port, madeira, marsala, sauternes, Bordeaux – or sometimes with rum or Cognac, even tequila is now permissable. The idea is to develop depth and complexity without overwhelming the distillery character, adding complementary layers of flavour without compromising the flavours developed during primary maturation.

Early practitioners were David Stewart for Balvenie Founder’s Reserve introduced mid-1980s, which evolved into the very popular Balvenie Doublewood and Rum Cask Finish, and Jim Milne, master blender at J&B, when the company released The Singleton (of Auchroisk) in 1986. None of these brands declared wood finishing on their labels, until Doublewood in 1981.

Another pioneer was Dr. Bill Lumsden at Glenmorangie who explored the potential of finishing extensively in the 1990s, but beginning in the mid-1980s with Oloroso sherry then port-finished expressions. These allowed the company to expand their product range beyond the usual 10YO, 18YO and 25YO expressions, and allowed Dr. Bill to have fun. A raft of interesting finishes followed, some more successful than others and now narrowed down to sherry, port and Sauternes.