How is it Made?
The chosen grains are sometimes malted, and then milled, fermented to a beer with water, distilled and aged. The process for malt whiskies follows, while grain whisky’s process follows from milling onwards :
STEEPING Literally soaking the grains of barley in water. After approximately 48 hours the moisture penetrates the grain. As a result, enzymes in the embryo move to the endosperm—its starch store—thus modifying it from a tough structure to a fragile one and allowing germination. The germination process changes the chemical structure of the starch and the resultant sugars promote seed growth.
MALTING There are less than 10 distilleries in Scotland who use the old-fashioned floor malting to convert barley to malt. Most is bought from specialist maltsters who will effect the process pneumatically in either box or drum, both of which contain turners that keep the grain separate and ensure the free flow of air throughout the bed. As a result of converting starch to maltose, rootlets and seedling shoots appear and the barley is now termed green malt. To maximise fermentable matter and retain adequate diastatic power this process is halted and the green malt is sent for drying.
KILNING OR DRYING A kiln is a tower-shaped hot air chamber with a furnace, sometimes fan assisted, consisting of a grate in which coke, anthracite and peat can be burned at the base. Inside the kiln the green malt is spread out on a wire floor to dry for milling.
MILLING The extent to which the grains are milled is crucial to the effectiveness of the resultant grist as it determines the amount of starch that is extracted and converted to sugar during the mashing stage. Too little and not enough starch will be exposed and converted into sugar, too much and the floury consistency will stick, go soggy and prevent good filtration. Ideally the grist should contain as many unbroken husks as possible as these provide greater buoyancy in the mash and aid filtration in the mash tun—a cylindrical metal vat with rotating paddles.
MASHING The grist is placed in a mash tun and combined with very hot water giving a slurry of about 64 ˚C; the starch dissolves and the mixture is left for about an hour. This converts the starch into sugar producing a sweet liquor known as wort. Towards the bottom is a perforated shelf through which the liquid drains into a worts receiver. The wort is then cooled to about 22 ˚C and pumped into the fermentation vessels known as wash backs. A second batch of water—smaller but hotter at about 70 ˚C is added to the mash tun and combined with the remaining grains. The higher temperature enables more starch to dissolve. Again, the wort is drained and despatched to the wash back. A third batch of hot water—about 89 ˚C—is added and vigorously stirred to issolve as much of the remaining starch as possible. After resting the resulting solution is very weak in sugar, and known as sparge, this is returned and used as part of the first batch of water for the next mash. This use of the sparge is a great aid to consistency. After the three waterings any grains, or draff, remaining, are discarded.
FERMENTATION Yeast is added to the cooled wort and fermentation— depending on factors including the type of yeast, the temperature and the type of malt—generally lasts about 48 hours.
DISTILLATION Methods have evolved around tradition and convention. In Scotland, malt whiskies are distilled twice or thrice in pot still and all grain whiskies are rectified in column stills. In Ireland, both malted and unmalted grains can be pot distilled, either two or three times, whilst lighter grain whiskies are distilled in multi-column continuous stills.
The Ageing of Whisky
Before the spirit is transferred to casks an initial reduction with de-mineralised water may be made to reduce the leaching of character from the oak. The casks are mostly second-use, traditionally old bourbon or sherry. Whisky can also be transferred to another cask for finishing ; this imparts flavours from the new cask, such as sherry, wine or another spirit.
The location of the ageing warehouse is a major factor. Whiskies matured by the sea will generally pick up coastal undertones and on the west coast of both Scotland and Ireland will be affected by the moderating influence of the Gulf Stream. Their respective east coasts are much cooler and the rate of evaporation, and therefore maturation, is slower. The whiskies can then be blended—malt with malt, grain with grain, malt with grain and so on— producing some of the world’s finest whiskies.