The wash is distilled twice - first in the wash still, to separate the alcohol from the water, yeast and residue called pot ale - the solids of which are also saved for use in animal feeds.
The distillate from the wash still, known as low wines, and containing about 20% alcohol by volume, then goes to the spirit still for the second distillation. The more volatile compounds which distil off first - the foreshots, and the final runnings called feints where more oily compounds are vaporized, are both channelled off to be redistilled when mixed with the low wines in the next batch.
Only the pure centre cut, or heart of the run, which is about 68% alcohol by volume is collected in the spirit receiver.
6. Spirit Safe
All the distillates pass through the spirit safe - whose locks were traditionally controlled by the Customs & Excise. The stillman uses all his years of experience to test and judge the various distillates without being able to come into physical contact with the spirit.
The newly distilled, colourless, fiery spirit reduced to maturing strength, 63% alcohol by volume, is filled into oak casks which may have previously contained Scotch whisky, bourbon or sherry, and the maturation process begins.
THE MAKING OF GRAIN WHISKY
1. Scotch grain whisky is usually made from 10-20% malted barley and then other unmalted cereals such as maize or wheat. The starch in the non-malted cereals is released by pre-cooking and converted into fermentable sugars. The mashing and fermentation processes are similar to those used for malt whisky.
2. The wash is distilled in a continuous or Coffey still, named after its inventor Aeneas Coffey. It has two tall columns - a rectifier and an analyser. Cold wash is pumped in at the top of the rectifier and meets steam. The columns in fact act like a heat exchanger. The alcohol is cooled, condenses and flows away as Scotch grain spirit at about 94% alcohol by volume.
3. The distilled grain spirit is lighter in character and aroma than most malt whiskies and therefore requires rather less time to mature. The bulk of matured grain whisky is used for blending.
THE MATURATION PROCESS
While maturing, the whisky becomes smoother, gains flavour, and draws its golden colour from the cask. A proportion of the higher alcohols turn into esters and other complex compounds which subtly enhance each whisky's distinctive characteristics.
By law all Scotch whisky must be matured for at least 3 years, but most single malts lie in the wood for 8, 10, 12, 15 years or longer. Customs & Excise allow for a maximum of 2% of the whisky to evaporate from the cask each year - the Angels' Share. Unlike wine, whisky does not mature further once it is in the bottle.