Scotch malt whisky is made from only three basic ingredients – malted barley, yeast, and water. Grain whisky uses wheat, maize, or other cereals rather than barley. Malt whisky is made by the pot still, while grain whisky is made by the patent (or coffey) still. There are some other slight differences between the production of malt and grain whisky, but overall the process is generally similar. There are five main stages in the production of malt whisky. While the first four stages can be completed in just a matter of days, the last stage can take anywhere from three to over twenty years.
The barley is first screened to remove any unwanted matter and soaked for 2-3 days in large tanks of water known as barley steeps. After this period, the barley is then spread out on a concrete malting floor where it begins to germinate. The germination process takes about 10 days on average where the barley is turned over regularly either by hand or machine. During the germination period, the barley secretes an enzyme diastase, which acts as a catalyst in the breakdown of starch into maltose. Germination is halted by drying the malted barley in a kiln fired with peat, which is a natural fuel cut from the Scottish moors. The kilns are distinguished by their pagoda-shaped chimneys and have become a characteristic mark of every distillery. Smoke from the fire drifts is allowed to filter through the drying barley. Once dried, the malt becomes crisp.
The dried malted barley is ground in a mill, and the resulting grist is mixed with hot water in a large circular vessel known as a mash tun. This process accelerates the conversion of starch in the barley to a sugary liquid called wort. The wort is then transferred from the mash tun into a fermenting vat while the leftover grist (also known as draff) is removed and recycled for use as cattle food.
The wort removed from the mast tun is cooled to a temperature ranging from around 68F to 72F. During this time, yeast is added to the wort in large wooden or metal vessels called washbacks. The yeast interacts with the sugary wort and converts it into a crude alcohol called wash. The fermentation process takes about 2 days to complete. At the outset, the wash is composed of a relatively low alcohol content, similar in strength to a strong beer. However at the end of the fermentation process, the alcohol strength gradually rises and becomes even stronger during the next stage in the production of scotch whisky.
Scotch whisky is normally distilled twice in large copper pot stills. The distillation process separates the alcohol from the wash. First, the liquid wash is heated in a wash still to a temperature where the alcohol vaporizes. The evaporated liquid rises up the still and is passed through condensing coils, or worm, where it reverts to a liquid state. The resultant liquid is known as low wine and then passed through another still where it is distilled a second time. The clear spirit is run through a spirit safe where the stillman is required to exercise their expertise to assess and measure the resulting spirit. The stillman only collects the spirit containing the highest quality alcohol needed for maturation, or middle cut. The first runnings from the still known as foreshots and feints that contain lower grade alcohols are returned for distillation with the next batch of low wines. The middle cut is collected by the stillman only when it has reached an acceptable standard.
After distillation, the new whisky is stored in casks of oak wood for several years where it is allowed to mature and develop its desired color and flavors. Air is permitted to pass through the cask where the harsher constituents in the new spirit are removed through evaporation. Malt whisky generally takes longer to mature than grain whisky, which can last over 10 years. Ultimately, the maturation period is determined by the size of the casks, strength of the spirit stored, and the temperature and humidity of the warehouse.
The spirit in the casks must mature at least three years before it can be legally called whisky. This, along with the distillation process, must take place in Scotland in order for the whisky to be called scotch. While in the cask, the whisky can be well over 60% ABV (alcohol by volume). It is diluted prior to bottling to reduce the ABV to approximately 40% by adding water. After maturation the different whiskies are blended together aiming at uniformity in the final product. A small amount of additional coloring is often added as well to bring a standard color to the whisky. The whisky is then filtered carefully and prepared for packaging.
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