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Production of Scotch Whisky



The raw materials required for the production of Malt Whisky are barley, water and yeast. The production process can be broken down into five stages.


MALTING Back to Top

First the barley is MALTED, that is the barley is germinated to convert the starches in each grain into a simple sugar. Distillers look for plump, ripe barley with plenty of starch and not too much nitrogen.

Barley is a food cereal similar to wheat and oats. It has always been the primary raw material for conversion to malt. The preference for barley over other cereals is undoubtedly the fact that the corn or seed is covered with a straw-like husk that is not removed by threshing and protects the grain during the process stages in malting. The husk subsequently serves as a filter in the mashing operations.

The origin of the barley is not important. Although Scottish barley is considered to be the most suitable, due to the soil and climatic conditions, there is not enough to satisfy the industry demand. Barley is imported from England and other countries. Originally the barley was grown locally and malted at the distillery, as evidenced by the familiar pagoda-shaped roofs of the malt kilns visible at some whisky distilleries. Today only a handful of distilleries have their own maltings; these include Highland Park, Glenfiddich, Bowmore, Laphroaig and Springbank. Specialist maltsters can provide distillers with more consistent malt made to their detailed specifications.

A grain of barley consists of two main parts, the Embryo and the Endosperm. The embryo is the important part of the corn, all the organs which will develop into a future plant being present there in a modified form. The Endosperm is the chief food storage organ of the seed from which the Embryo draws its food supplies in the early stages of germination. Also present in the corn, both in the Embryo and the Endosperm (to a limited extent) are substances known as proteins. Also secreted in the barley are Enzymes, which develop during germination and, in association with other Enzymes formed in the process, degrade the starch hydrolytically to provide simple fermentable sugars.

The object of malting is, therefore, to develop Enzymes and in particular Diastase of Malt and to modify or make friable the starch contained in the grain. This is carried out in three stages, steeping, germinating and kilning or drying. These processes must be affected in such a manner as to provide maximum fermentable matter (Malt Extract), adequate Diastatic Power and ensure minimum malting loss due to respiration etc.

The steeping cycle in the steep tanks is variable according to the quality of the barley and is, of course, dependent on the time taken for the moisture content of the barley to rise to the desired level. Generally a 60-hour cycle is adequate. During this period the water will have been changed at least three times, air rests, the number and lengths of periods having been first determined, will have taken place and regular periods of aeration of the steep water will also have been carried out.

Until recent years, floor malting was operated in the conversion of barley to malt. The disadvantage of this system is the difficulty of removing or counteracting the influence exerted on the malting process by atmospheric conditions. A large amount of space is necessary and the cost of employing the essential skilled workers is high.

Today floor malting is practically non-existent and the germination process is usually carried out in pneumatic maltings either Box Maltings or Drum Maltings.Box Maltings are generally more common and the essential feature is that temperature controlled air, saturated with moisture to a humidity of 100%, is passed through the bed of germinating grain contained in a concrete box and via perforations in the box floor. This system provides ideal conditions for the germination of the barley to proceed irrespective of the atmospheric conditions. The germination period is reduced in comparison with floor malting, production increased and a considerable economy affected in labor.

Turners are provided in the germinating box to ensure that all the grain contained therein is kept free, leveled and receive similar treatment in the passage of air throughout the bed. Having sprouted, the barley is now termed "green malt" and is ready for drying.

Germination having been completed the grain or "green malt" as it is now termed is transferred by screw and elevator to the Malt Kiln for drying. In Kilning, perfect control as far as is possible, should be established over the temperature of drying and economy in the use of Fuel. The Kiln is a tower shaped structure with a furnace provided at the base. The hot air chamber is located above the furnace.It distributes the heat from the furnace evenly under the wedge wire floor on to which the grain has been spread. The wedge wire floor is so constructed as to allow an easy passage for the hot air to pass through the grain. The upward draught of hot air may be natural but is often assisted by a powered fan.

The furnace is a simple grate in which coke or anthracite and peat is burned. The drying of the grain performs the following functions.

  • It stops germination and modification and fixes the Enzymes.
  • It reduces the Diastatic Power of the grain which was at its maximum in "green malt".
  • It physically changes and forms the malt into a condition suitable for milling or grinding at a subsequent stage.
  • It imparts a flavor to the malt as a result of the use of peat in the furnace.

Peat is formed from decomposed vegetable matter and the peat "reek" or smoke given off from combustion is imparted to the Malt. In the early drying stages whilst the grain is in a soft moist condition the peat "reek" permeates into the corns. In the latter drying stages the outer skin of the seeds will also be flavored.

Finally, on termination of the Kilning the Malt is removed to be stored in Bins for five to six weeks. This period of time is necessary to allow the heat to be dissipated naturally. The use of hot Malt is not conducive to the satisfactory function of one of the later functions, i.e., Fermentation.

In preparation for the next stage, Mashing, the malted barley must first be ground and this is carried out on a four-roller mill. Magnets are installed in the Mill to prevent pieces of metal passing through and making contact with the revolving rolls. Such an occurrence could cause a spark within the mill and create a fire and/or explosion.

The quality and consistency of the ground malt or Grist is all important if maximum extraction of fermentable matter is to be obtained in the Mashing operation. An ideal Grist should have as many of the husks as is possible, unbroken in appearance, although they should have been split open to release the starch. Unbroken husks provide a more buoyant Mash and give better filtration in the Mash-Tun by allowing the liquor to percolate through. Husks that have been crushed into numerous small pieces are liable, due to liquid pressure, to pack and thus impair drainage in and from the Mash-Tun.

In so far as the starch is concerned it is the aim of the Millman to break it down into minute gritty particles without creating flour. Some flour is unavoidable but this should be kept to a minimum. Fine grits allow the water to mix readily but flour resists mixing. If too much flour has been produced it creates bad filtration and often "soggy" or "sticking" mashes giving bad drainage. A visual examination of the grist provides an experienced operator with a good idea of the quality.

To obtain maximum efficiency, however, it is essential to know the exact quality of the grind. For this purpose a hand screening box which, when shaken, can separate a sample into three portions is used. Ideal Grist should have the following components.

  1. Coarse Materials and Husks 14% by weight
  2. Fine Grits 78% by weight
  3. Flour 8% by weight

Barley seeds and consequently Malt corns vary in size and it is therefore necessary to close or open the Mill Rolls to ensure that a Grist of the quality described is obtained. This entails regular sampling and checking by the Millman in order to obtain a Grist, which will provide the maximum Mash Tun Extract of fermentable matter.

MASHING Back to Top

The object of Mashing is to render soluble and to dissolve as much of the valuable contents of the Malt as is possible. This produces a sweet liquid or sugar solution termed Wort containing in addition to the sugars intermediate products.

The materials used in the Mashing process are Water and ground Malted Barley. The quality of the water plays an important part throughout this process and finally in the quality of the spirit produced. All waters tend to differ to some extent in the quantity and type of minerals and organisms contained therein. Generally speaking, hard waters are considered unsuitable and soft waters are preferred. An ideal process water would be one rising from a whinstone or granite strata, acid in nature and flowing through peaty soil with a minimum of metal content.

Springs and burns should be protected, wherever possible, to prevent contamination and water tanks and pipes should be scoured and sterilized frequently. It is undesirable to use water that has lain in tanks and pipes for some time. Such water may well contain bacterial and dissolved metals. In short, poor quality water should never be used in the process and regular analyses can assist in this respect.

The only cereal in the production of Malt Spirit is malted barley. Malt, as stated, contains a high percentage of starch together with enzymes that possess the power to convert starch to sugar when mixed or mashed with water. Enzymic action is influenced to a large extent by temperature, Ph and concentration of the mash.

The ground malt or Grist is conveyed to a hopper or bin situated above the Mash-Tun and mashing can commence. The Mash-Tun is a circular metal vessel provided with mechanical stirrers that revolve and rotate to thoroughly mix the Mash of Grist and Water as necessary. A perforated false bottom, to allow the liquor to drain through and discharge to a holding tank termed a Worts Receiver, covers the whole surface of the bottom of the Mash-Tun. Whilst the liquor drains off through the perforations the grains are retained in the Mash-Tun. The process involves the application of three waters.

First Water
Hot water at a temperature of 156F and the Grist are brought together simultaneously in a Mashing Machine, situated above and discharging into the Mash-Tun. The mixing of the Grist and the Water combines to give a striking temperature of 148F - 149F. When the Mash-Tun has been filled to the required capacity the temperature of the mass should be 147F - 148F. At this temperature the desired conversion proceeds rapidly. Great care must be exercised in regulating mashing temperatures, as variations will seriously affect the fermentability of the liquor. The Mash is allowed to sit for 1 hour to ensure maximum conversion at this temperature.

The Wort is, thereafter, drained into the Wort's receiver, cooled through a Heat Exchanger and pumped to the fermenting vessels called Wash Backs. It is necessary to cool the Wort as Yeast, which is added to the sugar solution, will not live or propagate in high temperatures. The Wort is therefore cooled to 72F at which temperature fermentation is rapidly incited by the action of the Yeast. In cooling the Wort in the Heat Exchanger the cooling agent is, of course, water and the heat from the Wort is transferred to same resulting in warm water at a temperature of 125F being returned to the Brewing Tanks for further use. This practice effects a saving in steam and consequently an economy in the use of coal.

Second Water
All the First Water liquor having been drained from the Mash-Tun a second Water is added to the bulk of the grains left in the Mash-Tun. No more Grist is added and the Second Water is applied at 172F giving a temperature of the mixture in the Mash-Tun of 157/159F. Quantitively the Second Water is usually about half that used for the First Water. The temperature is raised to further assist extraction and render soluble ant starch particles which had not been dissolved at the lower temperature of the First Water. The Mash, when the Second Water has been added, is again left "sitting" for a period of thirty minutes for conversion to take place. The liquor is thereafter drained, cooled and passed to the Wash Back.

Third Water
The grains left in the Mash-Tun still contain a small percentage of sugars. This is too valuable to lose and accordingly a Third Water raised to a temperature of 190F - 195F is applied. The stirrers, in this instance, are used vigorously to ensure thorough mixing and complete the final extraction. The liquor from the Third Water, which is a very weak sugar solution, is termed Sparge. It is returned to the Brewing Tanks to be used as the mashing liquor of the First Water of the next Mash. These operations should, therefore, obtain maximum extraction and minimum loss. The grains left in the Mash-Tun are, after the Third Water liquor has been drained off, removed mechanically and sold to Dairy Farmers. A high milk yield is forthcoming from the use of these grains known as Draff.


Yeast is a unicellular microorganism, that is to say, it is a living organism whose individual units are visible only under the microscope. It belongs to the planet kingdom and is classified as one of the fungi. There are many different species of yeast but the one normally encountered in the distilling and brewing industries is called Saccharomyces Cerevisiae. To give some ideas of the minute size of this micro-organism, three fully grown yeast cells placed end to end will measure only one thousandth part of an inch and in a 1 lb packet of yeast, there are approximately seven billion cells. (7,000,000,000,000).

VEGETATIVE: - The usual way in which yeast reproduces itself is by "budding" i.e. asexual means of propagation. A small protuberance first appears on the cell wall and gradually grows until a new cell is formed. This new cell can have a daughter cell of its own and so on. With ideal growth conditions one yeast cell can produce thirty yeast cells in three days.
SPORULATION: - this is also an asexual means of propagation which is very much more rare. When a yeast cell finds itself in a position where growth conditions are adverse, for example, when there is little or no food available, it forms spores. Within each cell four spores are formed and these eventually rupture the cell wall and escape into the surrounding liquid. Some of these spores are male and some female and when conditions are once again favorable and food is available pairs of spores unite to form new yeast cells.

When yeast is introduced into a sugar solution such as Wort there are three ways in which it utilizes the sugar.

  1. For multiplication i.e. it uses sugar to form new cell material.
  2. Fermentation: - This is an anaerobic reaction in that it occurs in the absence of air.
  3. Respiration:- This is an aerobic reaction and occurs if a constant source of oxygen is available.

The action of the yeast when added to the Wort can be divided into three phases.
(1) The lag phase where there is little fermentation. The yeast is busy adapting itself to its new surroundings and this is the period when contaminating bacteria can cause a great deal of damage.
(2) The log phase being the period of rapid fermentation when there is a rapid rise in temperature and fermentation is so vigorous that "switchers", rotating metal blades, must be employed to keep down the frothy head.
(3) Phase of restricted growth where the fermentation slows down and eventually terminates.

Yeast (1% by volume) is added as soon as possible to the cooled Wort being pumped into the Wash Back. This is done in the very early stages in order to quickly establish fermentation. It is more readily accomplished by providing the yeast with the ideal nutrient, the strong high gravity Wort of the initial liquor from the First Water. A strict control is kept on the Wort temperature and maintained until all the Wort from both the first and second waters has been collected in the Wash Backs. When all the Wort has been collected in the Wash Back the final temperature should be around 72F. however, if the sugar concentration of the Wort is likely to be high and a very quick acting yeast has been used, the collection or setting temperature should be dropped two or three degrees.

A rise in temperature takes place during fermentation from 72F - 94F. If the temperature exceeds the last figure and the temperature rise has been excessively rapid, this can destroy the yeast resulting in a poor fermentation and loss of spirit. Great care must therefore be exercised in the setting temperature and due allowance made for any abnormalities such as high concentration of sugars in the Wort.

The rate of fermentation is variable and is dependent on many factors such as the type of yeast, quantity, its condition, the setting temperature, the temperature in the Fermenter Room, the type of malt, the available Diastase, suspended solids in the Wort, mashing temperatures, purity of water and so on. Sometimes fermentation will appear to be continuing after fifty hours. Generally fermentation after forty-eight hours is negligible.

The cause of poor fermentation can be attributed to a number of factors, some of which are given below.

(1) The use of Malt low in Diastasic Power.
(2) Bacterial infected yeast.
(3) Excessively high percentage of dead cells in yeast.
(4) Incorrect mashing temperatures.
(5) Bacterial infection in vessels, pipes, pumps, valves etc.

It is of paramount importance that all vessels in the mashing and fermentation processes be kept 100% clean and free from bacteria. To this end a very strict cleaning and sterilization of all plant is adhered to and no relaxation of the cleaning operations is permissible. Bacterial infection can have a serious effect on the yield of spirit and also adversely affect the quality of the spirit.


Distilling takes place in pairs of copper pot stills with tall 'swan-necks'. One is usually larger than the other, otherwise their shapes, heights and sizes vary from distillery to distillery. The life of a still is between 15 and 30 years, depending on how hard it is used.

The two main operations in distilling are turning liquid into vapor and then vapor into liquid i.e. vaporization and then condensation. Distillation is simply a means of separation by these operations. A liquid can be separated from solids or one liquid from another and either the distillate or the residue collected.

The wash is pumped into the larger of the two stills, called the 'wash still', where it is brought to the boil. Stills are either heated directly from below (by gas, oil or coal) or from within by steam heated coils, not unlike those found in electric kettles.

The Wash contains solids such as dead yeast etc. from the fermentation process and it is necessary to keep these solids in suspension during the distillation period. This is done by means of a "rummager" inside the still. The "rummager" consists of three rotating arms to which are affixed webs of copper chain and also brass links. The webs scour the bottom and flue plates of the Still. This prevents the adherence of solids and thereby prevents the Still from being burnt.

The temperature has to be carefully controlled to prevent the foaming wash from rising up the swan-neck and into the condenser. A small window in the neck tells the distiller how far the wash has risen.

The alcoholic vapors and steam rise over the neck and into the condenser - essentially a series of pipes in a cold-water jacket. Here the vapors return to liquid at about 21 per cent alcohol and are termed low wines.

The Low Wines, thereafter, flow through the Spirit Safe, which is the control point of distilling operations, to a vessel called the Low Wines & Feints receiver. Inside the Spirit Safe, fabricated of brass or copper and glass and kept securely locked by the Customs & Excise, samples of the running distillate may be drawn and the strength tested by means of a hydrometer located inside the Safe.

They then pass through into the second still, the 'low wines still' or 'spirit still'. The same process is repeated in the second distillation, but this time the distiller watches the spirit carefully as it passes through the spirit safe. The early part of the run (known as 'foreshots') is pungent and impure. He test the spirit by adding water (which turns it cloudy), measuring its specific gravity and watching the clock, and until the foreshots run clear, he directs it back to the low wines and feints charger to be redistilled. This takes between 15 and 45 minutes depending on the size of the still.

When he is sure that the run is clear, the stillman redirects the spout and begins to collect the spirit for maturing. This is 'new make', and will run between two and fours hours, depending on the size of the still, commencing at about 70 to 75 percent alcohol and decreasing steadily down to between 60 to 65 percent.

The precise strengths, the speed at which he operates his still and the length of time he saves spirit (known as the 'cut') is part of his art and influences the flavor and quality of the product. It varies from distillery to distillery but the 'new make' may be about one third of the spirit distilled. Only part of the run is collected, because about halfway through the second distillation, various oily compounds called 'feints' begin to vaporize. They are mild and pleasant at first, lending character and flavor to the whisky, but in time their intensity increases to such a degree that to continue to collect the spirit will spoil the whole batch.

The stillman will again direct the distillate to the low wines and feints charger for re-distillation. Distilling continues until all that is left is 'spent lees' (more or less water). The distillation of 1,500 gallons (6,800 liters) of low wines and feints normally takes about six hours.


In this discourse up to this point no mention has been made of whisky. This is simply because the spirit produced cannot legally be termed Scotch Whisky until it has been matured in oak casks for at least three years.

If it is intended to sell the Malt Spirit as a single Malt Whisky then at least eight years maturation or preferably ten to twelve years will be necessitated.

No reputable distiller would market Malt Whisky or even Blended Whisky at such an immature age as three years. The maturation of whisky i.e. the change from a raw harsh spirit to the smooth, mellow aromatic whisky, so acceptable to most, is to a great extent a closed book. It is known, of course, that the spirit vaporizes and permeates through the cask into the atmosphere and that moisture from the atmosphere is drawn into and mixed with the spirit in the cask. It is also known that, proportionally, the congenerics change in relation to their original content in new spirit. This is, of course, due to the variance in vaporization tendencies.

Many millions of gallons of spirit are lost due to the vaporization during maturation. In the past efforts have been made to artificially mature whisky. These efforts, one is glad to state, have proved unsuccessful. Electrolysis, the use of Catalysts and other methods have all been tried but not with any real degree of success. It is to be hoped that no artificial process of quick maturation will be forthcoming and thus ensure that, although more and more chemistry is being applied to the production of Scotch Whisky, it will still remain an art and not a science.

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