Production process for Scotch whisky
Scotch whisky is made from cereals which are allowed to begin germination, a process which releases enzymes that turn grain starch into sugar. The germination is halted by heating, and yeast is added to ferment the sugary mixture. The fermentation result – basically beer – is distilled to produce a clear-coloured distillate which is not suitable for drinking and which contains several hundred complex organic compounds. Water is then added back, and the mixture is stored for maturation in naturally permeable, second-hand, oak casks.
The casks, which will previously have stored Bourbon or Tennessee whiskey, sherry or possibly port, offer a richly complex semi-permeable membrane through which gases can pass. There the many different organic chemicals interact both with the distilled spirit, and with each other, during this maturation process.
In ways which are not fully understood, the chemistry of the distillate changes subtly as it reacts with the second-hand wood, and with the cold, damp, Scottish air which slowly crosses the membrane.
At the end of a minimum of 3 years maturation various finishing and (optional) blending processes finalise the colour and taste, prior to bottling, more than 80% of which is completed in Scotland.
Whisky significantly improves during time spent in the cask. That’s why the official age of a whisky is defined by the time it spends in cask, and will be the shortest cask-maturation period of any of the spirit blended into the bottle. Unlike wine, whisky does not change character in a bottle. Also, unlike wine, it is not materially different from year to year.
But it is materially different from still to still. Local factors involving the source of the water, the procedure employed before distilling, the types of cask used, the period of maturation, even the shape of a copper still (in the case of malt whiskies) can end up having a marked effect on the taste and character of the final product.