Malt Whisky
The Pot Still process by which Malt Whisky is made may be divided into four main stages: Malting, Mashing, Fermentation and Distillation.

(a) Malting
The barley is first screened to remove any foreign matter and then soaked for two or three days in tanks of water known as steeps. After this it is spread out on a concrete floor known as the malting floor and allowed to germinate. Germination may take from 8 to 12 days depending on the season of the year, the quality of the barley used and other factors. During germination the barley secretes the enzyme diastase which makes the starch in the barley soluble, thus preparing it for conversion into sugar. Throughout this period the barley must be turned at regular intervals to control the temperature and rate of germination.

At the appropriate moment germination is stopped by drying the malted barley or green malt in the malt kiln. More usually nowadays malting is carried out in Saladin boxes or in drum maltings, in both of which the process is controlled mechanically. Instead of germinating on the distillery floor, the grain is contained in large rectangular boxes (Saladin) or in large cylindrical drums. Temperature is controlled by blowing air at selected temperatures upwards through the germinating grain, which is turned mechanically. A recent development caused by the rapid expansion of the Scotch Whisky industry is for distilleries to obtain their malt from centralised maltings which supply a number of distilleries, thereby enabling the malting process to be carried out more economically.

(b) Mashing
The dried malt is ground in a mill and the grist, as it is now called, is mixed with hot water in a large circular vessel called a mash tun. The soluble starch is thus converted into a sugary liquid known as wort. This is drawn off from the mash tun and the solids remaining are removed for use as cattle food.

(c) Fermentation
After cooling, the wort is passed into large vessels holding anything from 9,000 to 45,000 litres of liquid where it is fermented by the addition of yeast. The living yeast attacks the sugar in the wort and converts it into crude alcohol. Fermentation takes about 48 hours and produces a liquid known as wash, containing alcohol of low strength, some unfermentable matter and certain by-products of fermentation.

(d)Distillation
Malt Whisky is distilled twice in large copper Pot Stills. The liquid wash is heated to a point at which the alcohol becomes vapour. This rises up the still and is passed into the cooling plant where it is condensed into liquid state. The cooling plant frequently takes the form of a coiled copper tube or worm that is kept in continuously running cold water.

The first distillation separates the alcohol from the fermented liquid and eliminates the residue of the yeast and unfermentable matter. This distillate, known as low wines, is then passed into another still where it is distilled a second time. The first runnings from this second distillation are not considered potable and it is only when the spirit reaches an acceptable standard that it is collected in the Spirit Receiver. Again, towards the end of the distillation, the spirit begins to fall off in strength and quality. It is then no longer collected as spirit but drawn off and kept, together with the first running, for redistillation with the next low wines.

Pot Still distillation is a batch process.

Grain Whisky
The Patent Still process by which Grain Whisky is made is continuous in operation and differs from the Pot Still process in five other ways.

(a) The mash consists of a proportion of malted barley together with unmalted cereals.

(b) Any unmalted cereals used are cooked under steam pressure in Converters for about three and a half hours. During this time the mixture of grain and water is agitated by stirrers inside the cooker.

(c) The starch cells in the grain burst and when this liquid is transferred to the mash tun, with the malted barley, the diastase in the latter converts the starch into sugar.

(d) The wort is collected at a specific gravity lower than in the case of the Pot Still process.

Distillation is carried out in a Patent or Coffey Still and the spirit collected at a much higher strength.

Maturation
Both Malt and Grain Whisky must be matured after distillation has been completed. The new spirit is filled into casks of oak wood which, being permeable, allows air to pass in and evaporation takes place. By this means the harsher constituents in the new spirit are removed and it becomes in due course a mellow whisky. Malt Whisky which contains more of these flavoury constituents takes longer to mature than Grain Whisky and is often left in the cask for 10 years or even longer.

The period of maturation for both Malt and Grain Whisky is also affected by the size of casks used, the strength at which the spirit is stored, and the temperature and humidity of the warehouse.

Blending
After maturation the different whiskies are blended together. The blend is then reduced to the strength required for bottling by the addition of soft water. The different whiskies in the blend will have derived some colour from the casks in which they have been matured, but the degree of colour will vary from one whisky to another. Whisky matured in former fresh oak sherry casks will usually be a darker colour than that which has been matured in refilled whisky casks. The blender aims at uniformity in his product and he may bring his whisky to a definite standard colour by adding, if necessary, a small amount of colouring solution prepared from caramelised sugar, which is infinitesimal in relation to the volume of whisky involved. The whisky is then filtered carefully.

Packaging
The final stage in the production of Scotch Whisky is packaging and despatch. Most Scotch Whiskies are marketed at home and abroad in branded bottles.

In some instances, for commercial reasons, Scotch Whisky may be shipped overseas in bulk. When blended Scotch Whisky is shipped abroad in bulk, either at original strength or suitably reduced, it is exported in glass lined stainless steel tanks or casks of varying size according to the market. The bottling is then carried out by distributors or agents overseas.

(1) Lowland Malt Whiskies, made south of an imaginary line drawn from Dundee in the east to Greenock in the west.

(2) Highland Malt Whiskies, made north of that line.

(3) Speyside Malt Whiskies, from the valley of the River Spey. Although these whiskies come from within the area designated as Highland Malt Whiskies, the concentration of distilleries and the specific climatic conditions produce a whisky of an identifiable character and require a separate classification.

(4) Islay Malt Whiskies, from the island of Islay.

Each group has its own clearly defined characteristics, ranging from the lighter Lowland Malt Whiskies to those distilled on Islay which are generally regarded as the heaviest Malt Whiskies.

Malt Whiskies, which differ considerably in flavour according to the distillery from which they come, have a more pronounced bouquet and flavour than the Grain Whiskies. The production of Grain Whisky is not so influenced by geographical factors and it may be distilled anywhere in Scotland.

The distilling process itself is one factor. Scotch Whisky, after it has been distilled, contains not only ethyl alcohol and water but certain secondary constituents. The exact nature of these is not fully understood, but it is believed they include some of the essential oils from the malted barley and other cereals and substances that derive from the peat. The amount of these secondary constituents retained in the spirit depends upon the shape of the still and the way it is operated and also on the strength at which the spirit is drawn off. Grain Whisky, because of the process by which it is made, contains fewer secondary constituents than Malt Whisky and is accordingly milder in flavour and aroma.

The natural elements of water, peat and the Scottish climate all certainly have a profound effect on the flavour of Scotch Whisky. Water is probably the most important single factor and a source of good, soft water is essential to a distillery. Peat, which is used in the kiln or oven in which the malt is dried, also has an influence that can be detected in the ‘peaty’ or smoky flavour of many Scotch Whiskies. The Scottish climate is extremely important, particularly when the whisky is maturing. At this stage the soft air permeates the casks and works on the whisky, eliminating harsher constituents to produce a mellow whisky.