You know you’ve caught the whisky bug good and proper when you happily sit through a two hour talk on casks, or consider the highlight of your distillery trip is the exhibition on wood.But maturation is one of the main components which sets whisky apart from any other spirit.For some time it has been the driver for innovation and evolution, and judging by the significant number of new release Scotch whiskies bottled at cask strength in this issue, and the experiments with cask from America in the last, the maturation process will continue to play a major role in whisky’s future.Up to 70 per cent of the flavour of a whisky may come from the cask and although a bad spirit will not be transformed into a good one in oak, it’s fair to say a good or very good new make can become an outstanding whisky if the wood it is stored in is of top quality.To become a whisky the new spirit must be stored in oak barrels for a minimum period of time, three years in Europe, just two in America. But while the place where the casks are stored is essential, where the cask originally came from is not. So scotch must be matured in Scotland but the casks can and very often do come from Kentucky.Contrary to popular belief and to what is written in most whisky books,bourbon does not have to be matured in only American oak.In Scotland the cask will most probably have contained something else previously. When put in to the cask the new spirit will react in three ways to the wood. Even at the relatively sedate temperatures of Scotland the liquid will move in the cask and expand and contract with temperature change.So the spirit will be forced into the wood when it expands and contract out of it when it contracts.And from this process is will draw colour and flavour from the wood, will have fats and congeners removed from it by the wood, and will react chemically with the wood to form new taste compounds.No two casks will react exactly the same, but some generalisations can be made.Firstly, in Scotland about two per cent of the barrel contents will evaporate, the greater part of which is alcohol. This means the strength of the spirit will decline gradually each year.Secondly, the contribution of the wood to the taste and colour of the spirit will be more pronounced in the early years and will eventually tail off.But after many years in the cask the flavour of the wood itself will become stronger until eventually it will dominate and destroy the flavour of the whisky.So cask management is essential especially to make sure the strength does not fall under the minimum permitted strength of 40% ABV.In Kentucky the process is a different one. American law states that new spirit must be matured in new oak barrels that have never been used before. They are toasted and charred on the inside before spirit is added.Because of Kentucky’s very hot summers, temperatures in the warehouse are far higher than Scotland and as with any chemical reaction the process speeds up by heat. That, coupled with freezing winters, means that the maturation process is far faster.The effect on the spirit is very different, too. Evaporation still takes place, but water evaporates faster than the alcohol, so that the spirit becomes stronger over time – the opposite to Scotland.With thousands of casks to manage it takes the great skill to make sure that each cask is brought out at its very best.So while the layman might see an oak container the whisky enthusiast sees a magical mini production plant.GLOSSARY
MALT:
Any grain that has been ‘tricked’into starting to grow and then dried to stop further germination. The process prepares the grain for fermentation by unlocking the sugars and starches contained in the grain
MALT WHISKY:
Made using only malted barley,yeast and water
MALTING:
The process of tricking a grain into growing and then controlling its germination
MALTINGS:
The building where malting takes place
MARRYING:
The process of mixing different whiskies together in huge containers. May be used for blended whiskies but also for combining different malt casks too
MASH:
Name for the mix of boiling water and grist – ground grain –which is rich in fermentable starches
MASH BILL:
In American whiskey production the mash is made up of three or more grains.The mash bill refers to the proportion of each grain in the mix
MASH TUN: The vessel in which hot water is added to the grist to makethe mash
MASHING:The process of soaking grist in hot water to extract fermentable starch
MILLING: The conversion of dried malt in to a rough flour known as grist before mashing takes place