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Malt Scotch Whisky

The process of producing malt whisky has, in essence, changed little through the centuries, although in recent years, greater automation and computerisation in many distilleries has reduced the level of individual skill and experience required by the operators.

Despite any amount of automation, however, the fact remains that the 'make' of no two distilleries is ever the same. While it is possible to copy production methods and equipment, use the same water source, barley and yeast, and mature spirit for the same duration in the same type of casks within apparently identical micro-climates, the result will always be distinctly different spirits. Vast sums of money have been invested in the search for a definitive scientific evaluation of the variables in malt whisky making, but despite the best efforts of the scientists, an element of mystery remains.

By law, Scotch malt whisky must be distilled entirely from a mash of malted barley, and the business of making malt whisky begins by malting barley in order to induce germination. In traditional distillery-based floor maltings, the barley is steeped in water for two or three days, then spread on a malting floor, where rootlets develop as germination begins. So that the malt retains the sugars essential for fermentation, the partially germinated 'green malt', as it is known, is transferred to a kiln for around seven days and dried over a fire or by jets of hot air, usually with some peat used in the furnace to impart flavour. The amount of peat introduced during kilning has a major influence on the character of the finished whisky.
  

Today, only a handful of distilleries still malt their own barley, with the vast majority buying in malt prepared to their specification by commercial maltsters in large, automated plants.

Once dried, the malt is ground in a mill to produce 'grist,' after which the process of mashing begins. The grist is mixed with hot water in a large vessel known as a mash tun to extract fermentable sugars, and the sweet liquid that results from mashing is known as 'wort.' The 'draff,' which is left behind is high in protein, and makes excellent cattle feed.

The wort is pumped from the mash tun into a number of washbacks, traditionally made from Oregon pine or larch wood, but now frequently constructed of stainless steel. There yeast is added to promote fermentation and create alcohol. The end product of fermentation is a liquor known as 'wash,' which is transferred to copper pot wash stills, where it is brought to the boil. Alcohol boils at a lower temperature than water, so the alcohol vapours rise from the still first and are condensed into liquid when they pass through coiled copper pipes or 'worms', immersed in vast wooden vats, or more modern 'shell and tube' condensers.


   The alcohol produced must be re-distilled in order to obtain the most pure 'cut' of spirit that will mature into whisky, and this takes place in vessels known as spirit stills. Pot stills vary greatly in size, shape and technical design, and this diversity is one of the variables that contribute to the style of spirit made.

The product of the spirit stills is referred to as 'new make' or 'clearic.' It is a clear liquid which is reduced with water from its natural strength to around 63 or 64 per cent alcohol by volume, as this is usually considered the optimum maturation strength. Most whisky is further reduced to 40 or 43 per cent prior to bottling. 40 per cent is the minimum legal strength at which Scotch whisky can be sold. There is also a legal minimum maturation period of three years, and that maturation has to take place in oak. However, most whisky marketed as single malt will have spent at least eight years in European or American oak casks which have previously contained either sherry or Bourbon.

Some distillers believe that up to 75 per cent of the character of the spirit is derived from maturation, and the size of cask, as well as its previous contents, is yet another major variable of malt whisky production.

By law, a single malt whisky must be the product of just one distillery, though many different casks of varying ages may be vatted together for any particular bottling.
  

Grain or Column Still Whisk(e)y

Virtually all Bourbon, rye, Tennessee and Canadian whiskey, along with grain spirit for Scotch whisky blending, is distilled in column stills. Irish distillers use both pot and column stills, producing grain spirit, usually from corn, in the column stills, while what is termed Irish 'pure pot still whiskey' is made in pot stills from a mixture of both malted and raw barley.

Compared to malt whisky distillation in pot stills, the production of whisky in a column, continuous or patent still, as it is variously known, is significantly closer to an 'industrial' process. Grain whisky is made from a variety of cereals, including corn, wheat, and rye, which are less expensive to buy than the malted barley used to make malt whisky.

The stills making grain spirit are versatile and highly efficient, as they can work continuously, whereas malt whisky distillation in pot stills is a 'batch' process, requiring time-consuming cleaning between each period of production. A much greater quantity of grain whisky can therefore be distilled in any given period. However,
  
depending on the cereal in the 'mash bill,' the resultant spirit may be lacking in strong flavour compared to the product of the pot still. Certainly this is the case in Scotland, where virtually all grain whisky is distilled using wheat.

The processes of mashing and fermenting for grain whisky production are broadly comparable to those for making malt whisky, but distillation then takes place in a still which consists of two large, connected parallel stainless steel columns, called the analyser and the rectifier. The wash enters at the top of the rectifier column, where it is warmed by hot steam and is able to descend over a series of perforated copper plates. These plates serve the purpose of holding back heavier compounds, which flow from the bottom of the still, while the desirable volatile compounds are vaporised and pass over into the second, or analyser column. Here the vapours are cooled as they rise up the column, eventually evaporating and being collected in liquid form. It is possible to distil to a strength of just below 95 per cent when producing grain whisky in a column still.

In the USA, the first column of the still is usually known as the 'beer still' while the second distillation takes place in either a 'doubler' or 'thumper' still, which is not dissimilar in style to a pot still.

  

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