Grains are shipped directly from farms to the whiskey manufacturer to be stored in silos until needed. The grain is inspected and cleaned to remove all dust and other foreign particles.
All grains except barley are first ground into meal in a gristmill. The meal is then mixed with water and cooked to break down the cellulose walls that contain starch granules. This can be done in a closed pressure cooker at temperatures of up to 311°F (155°C) or more slowly in an open cooker at 212°F (100°C).
Instead of being cooked, barley is malted. The first step in malting barley consists of soaking it in water until it is thoroughly saturated. It is then spread out and sprinkled with water for about three weeks, at which time it begins to sprout. During this germination the enzyme amylase is produced, which converts the starch in the barley into sugars. The sprouting is halted by drying the barley and heating it with hot air from a kiln. For Scotch whiskey, the fuel used in the kiln includes peat, a soft, carbon-rich substance formed when plant matter decomposes in water. The peat gives Scotch whiskey a characteristic smoky taste. The malted barley is then ground like other grains.
Mashing consists of mixing cooked grain with malted barley and warm water. The amylase in the malted barley converts the starch in the other grains into sugars. After several hours the mixture is converted into a turbid, sugar-rich liquid known as mash. (In making Scotch malt whiskey the mixture consists only of malted barley and water. After mashing the mixture is filtered to produce a sugar-rich liquid known as wort.)
The mash or wort is transferred to a fermentation vessel, usually closed in Scotland and open in the United States. These vessels may be made of wood or stainless steel. Yeast is added to begin fermentation, in which the single-celled yeast organisms convert the sugars in the mash or wort to alcohol. The yeast may be added in the form of new, never-used yeast cells (the sweet mash process) or in the form of a portion of a previous batch of fermentation (the sour mash process.) The sour mash method is more often used because it is effective at room temperature and its low pH (high acidity) promotes yeast growth and inhibits the growth of bacteria. The sweet mash method is more difficult to control, and it must be used at temperatures above 80°F (27°C) to speed up the fermentation and to avoid bacterial contamination. After three or four days, the end product of fermentation is a liquid containing about 10% alcohol known as distiller’s beer in the United States or wash in Scotland.
Scottish whiskey makers often distill their wash in traditional copper pot stills. The wash is heated so that most of the alcohol (which boils at 172°F [78°C]) is transformed into vapor but most of the water (which boils at 212°F [100°C]) is not. This vapor is transferred back into liquid alcohol in a water-cooled condenser and collected. Most modern distilleries use a continuous still. This consists of a tall cylindrical column filled with a series of perforated plates. Steam enters the still from the bottom, and distiller’s beer enters from the top. The beer is distilled as it slowly drips through the plates, and the alcohol is condensed back into a liquid. With either method, the product of the initial distillation—known as low wine—is distilled a second time to produce a product known as high wine or new whiskey, which contains about 70% alcohol.
Water is added to the high wine to reduce its alcohol content to about 50% or 60% for American whiskeys and about 65% or higher for Scotch whiskeys. Scotch whiskeys are aged in cool, wet conditions, so they absorb water and become less alcoholic. American whiskeys are aged in warmer, drier conditions so they lose water and become more alcoholic. Whiskey is aged in wooden barrels, usually made from charred white oak. White oak is used because it is one of the few woods that can hold a liquid without leaking but which also allows the water in the whiskey to move back and forth within the pores of the wood, which helps to add flavor. In the United States these barrels are usually new and are only used once. In most other countries it is common to reuse old barrels. New barrels add more flavor than used barrels, resulting in differences in the taste of American and foreign whiskeys. The aging process is a complex one, still not fully understood, but at least three factors are involved. First, the original mixture of water, alcohol, and congeners react with each other over time. Second, these ingredients react with oxygen in the outside air in oxidation reactions. Third, the water absorbs substances from the wood as it moves within it. (Charring the wood makes these substances more soluble in water.) All these factors change the flavor of the whiskey. Whiskey generally takes at least three or four years to mature, and many whiskeys are aged for ten or fifteen years.
Straight whiskeys and single malt Scotch whiskeys are not blended; that is, they are produced from single batches and are ready to be bottled straight from the barrel. All other whiskeys are blended. Different batches of whiskey are mixed together to produce a better flavor. Often neutral grain spirit is added to lighten the flavor, caramel is added to standardize the color, and a small amount of sherry or port wine is added to help the flavors blend. Blended Scotch whiskey usually consists of several batches of strongly flavored malt whiskeys mixed with less strongly flavored grain whiskeys. A few blends contain only malt whiskeys. Blending is often considered the most difficult and critical process in producing premium Scotch whiskeys. A premium blended Scotch whiskey may contain more than 60 individual malt whiskeys which must be blended in the proper proportions.
Glass is always used to store mature whiskey because it does not react with it to change the flavor. Modern distilleries use automated machinery to produce as many as 400 bottles of whiskey per minute. The glass bottles move down a conveyor belt as they are cleaned, filled, capped, sealed, labeled, and placed in cardboard boxes. The whiskey is ready to be shipped to liquor stores, bars, and restaurants.