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Chapter 4: Technical Background to the Malting Process; “Port Ellen: Distillery and Maltings”


The barley normally in use at Port Ellen is of the variety Optic, with a nitrogen content of approximately 1.59% by weight.

This is a high quality malting barley, ideal for producing malt destined for pot still whisky production. The low nitrogen content indicates that the grains contain a relatively large amount of starch and it is this starch that will eventually be turned into whisky by the distiller. Barley with a high nitrogen content contains more protein and hence less starch than low nitrogen barley. High nitrogen barley is used in the production of grain whisky or as animal feed.


As noted above, barley contains the starch that will be turned into whisky by the distiller. Why does the distiller require that the barley be turned into malt when the barley contains the starch that he needs? There are several reasons for this including:

  • The starch in barley is enclosed within cells and these cells have walls that impede access to the starch. (The mashing water used by the distiller to convert the starch to sugar and extract it must be able to get to the starch).
  • Within the barley cells the starch is enclosed in protein and this protein also impedes access to the starch.
• Barley grains are hard, making it difficult to mill them into the small particles required by the distiller.
  • Substances in the barley will turn the malt extract within the distiller's mash tun into a thick, viscous, porridge-like substance that will prevent the sugar solution being run out of the mash tun and into the washback for fermentation.
  • Barley may contain dirt and other substances picked up in the field. Malting washes these residues out of the grain.
• Raw barley contains few of the enzymes that the distiller will require to turn the starch into fermentable sugar. Malting naturally develops these enzymes within the grain.


Luckily for the maltster, the details of the process of turning barley into malt are looked after by the grain itself.

The starch is present in the grain as a food source for the embryo (the barley germ). This food reserve will feed the embryo until it can grow roots and shoots to gather food itself. The main inner part of the grain is called the endosperm and this is where the starch is stored (along with the cell wall material and protein). Split a barley grain in half and you will be able to see the white starch.

When the embryo starts to grow it has to gain access to its food (the starch) and in doing so it removes the cell wall and protein material. The enzymes required by the distiller will also begin to be developed at this time. By allowing growth to proceed the maltster contrives that the undesirable cell wall and protein is removed. If growth is allowed to proceed too far the embryo will begin to use up the starch and hence there will be less starch available for the distiller. There is therefore an optimum point in the growth process where the cell wall and protein has largely been removed (making the malt easy for the distiller to process), but the starch is still largely intact (allowing the distiller to make relatively large amounts of whisky from a given amount of malt).
The malting process basically consists of encouraging the barley to start to grow and then, when the optimum point in the growth process is reached, stopping growth.


MALTING consists of 3 main processes:

STEEPING — where the "sleeping" barley is awakened into growth.
GERMINATION —where that growth is nurtured.

KILNING — where the growth is stopped at the optimum point.



Steeping sets the barley off on the path to being malt. If steeping is carried out badly it will never be possible to redress the balance and make good malt from that batch. If steeping is carried out well, then the rest of the malting process will be relatively straightforward.

At harvest time barley grains have a natural resistance to growth, this is known as "dormancy". Dormancy is the plant's natural control mechanism to ensure that the grain does not start to germinate until the new growing season has arrived. Dormant grains will not grow well (if at all) and so the maltster must ensure that the barley he uses has had dormancy broken by careful storage under the right conditions.

Barley must remain in good condition during storage. This is achieved by storing it at low temperature (less than I5oc) and at low moisture levels - below 15% by weight, usually around 12%.

Growth is initiated by soaking the grain to raise its moisture content. The optimum moisture content for barley growth at Port Ellen is 44% by weight.

Although it may appear that the best way to increase moisture content is to immerse the grain in water until the correct moisture content is achieved, this is not the case. The outer layers of the grain are relatively waterproof and water enters this way only slowly. An improved steeping method is to give the grain a short initial soak to awaken the embryo, then drain off the water so that the embryo can gain access to oxygen and become more active. This more active embryo will encourage the uptake of water resulting in more rapid water absorption when next soaked. When the grain is under water this is termed a "wet" and when the water is drained off this is termed an "air rest". Different barley varieties respond differently to the same pattern of wets and air rests. The optimum steeping pattern will also depend on many other factors including the size of the grain, its sensitivity to water, the length of time since it was harvested, the area where the barley was harvested, weather conditions during barley growth, the weather conditions during steeping, the temperature of the water added to the steep, etc.

Taking all the necessary factors into account a steeping pattern will be determined for each batch of barley. During steeping, conditions will vary from those anticipated when the plan was created and changes to the plan will be made as required to ensure that all the barley in a batch reaches the correct moisture content with the correct rate of growth.

It is of vital importance that all the barley in a batch grows evenly at the correct rate. The distiller has spent a considerable amount of time and effort setting up his plant to accommodate a particular quality of malt, if malt quality is changing from moment to moment as each batch is used at the distillery then all this work will have been ruined. This is why it is important to have the barley in a batch grow at the same even rate. If the grains are growing at different rates they will reach the optimum point in the growth cycle at different times and the batch will contain a mixture of malt qualities.

At Port Ellen the steeping plan at the time of writing is: 7 hrs wet, 10 hour air rest, 9 hours wet, 7 hours air rest, 7 hours wet, 2 hours air rest. Water is sourced from the Leorin Lochs in the hills above the maltings and is a rich brown colour from the peat in the surrounding ground.

The peat content of the water has only a minimal effect on the peatiness of the final malt which depends on peat burned during kilning.

Port Ellen has 8 steeps, they are cylindro-conical vessels which hold 25.5 tonnes of barley each. Each steep has 2 aeration systems. The first system, "suction aeration", is used to suck fresh cool air into the steep

when it contains barley during an air rest. The second system, "pressure aeration", is used when the barley is under water. Compressed air is blown from the bottom of the steep up through the water and barley, causing the barley to become well mixed. The barley on the bottom of the steep grows slightly more slowly that the barley on the top, by mixing the barley these small differences in growth are evened out.

At the end of the steeping process the barley is at 44% moisture content and is growing vigorously and evenly. The growing barley absorbs oxygen and emits carbon dioxide and heat. The steeping vessel cannot provide enough fresh, cool air to remove this carbon dioxide and heat so, to maintain optimum growth, the barley is passed to the next stage of the process, germination.


At Port Ellen the type of germination vessel used is the Boby Drum. Each drum holds the contents of 2 steeps which is 5I tonnes original barley weight or 82 tonnes of barley at 44% moisture content. These are the largest making drums in the UK.

The drum is a large metal cylinder with its curved surface parallel to the ground. Inside the drum is a flat floor made of perforated steel plate. The barley from the steeps is placed on top of the drum floor. By blowing air into the bottom of the drum, up through the floor and the grain, the carbon dioxide and heat generated by the grain can be removed and the best possible growth conditions achieved.

Drums are expensive to build and are expensive and labour intensive to run therefore it is unlikely that further drum plants will be built in future. The advantage of drums is that they give good control of germination conditions and are capable of producing high quality malt.

Immediately after loading the drum the wet barley is in 2 large mounds, one at each end of the drum. If air was to be blown up through the floor it would tend to pass through the middle of the drum where there was little grain to impede its flow. This would leave the barley in the centre of the mounds in poor growing conditions. To prevent this happening the drum has 2 sets of fins attached to the inner walls.

The fins are in a corkscrew pattern, along the curved walls of the drum from each end in towards the centre. By turning the whole drum the fins will guide the barley from the mounds in towards the centre. After 2 complete turns of the drum the barley will be spread in an even layer across the floor.

If ordinary air was to be blown through the drum, the barley would tend to dry out and spoil our earlier efforts to obtain the optimum moisture level. In order to prevent this happening the air is humidified with fresh water before it reaches the barley.

The air leaving the drum is moist and warm compared to the air entering the drum. By recycling a portion of the air leaving the drum into the input air, control over input air temperature can be achieved.

By controlling the air flow rate, temperature and humidity, the best possible growth conditions can be maintained within the drum.

While in the drum the grain roots will grow. These roots will tend to curl together, locking the barely into a solid mass if not checked. To prevent this happening the drum is turned periodically (currently every 8 hours). During turning, the fins on the wall of the drum move the grains, pulling the roots gently apart.

After approximately 5 days, the barley in the drum has reached the optimum position in the growth cycle for making high quality malt. This can be checked by 2 simple tests.

The acrospire is the shoot that would eventually become the part of the barley plant that would be visible above ground in the field.The acrospire grows just under the skin (husk) of the grain. It can be seen by careful observation of the individual grains or by removing the husk. Ideally the acrospire length should be more than 2/3 the length of the grain but less than the length of the grain. If the acrospire is too short, the barley needs more time in the drum.

The main (white) inner part of the grain is called the endosperm. By using afingernail to split a grain open, a portion of the endosperm may be rubbed out between thumb and forefinger. If the endosperm rubs without leaving a mark on the fingers this indicates that the starch is still bound up by protein and cell wall and requires further time in the drum. If the endosperm rubs away on the fingers leaving a fine white powder this indicates that the endosperm starch (barley flour) is now accessible and the green malt as it is ntiw known, is ready for kilning.


After germination the green malt should have reached the point where its starch is now accessible to the distiller. The embryo itself should not have degraded any significant quantities of starch, so the vast majority (approximately 90%) of the original starch within the grain is still available to the distiller.

The growth process needs to be stopped at this point and this is done by the application of heat. The main object of kilning is to halt barley growth but there are other advantages too.

By reducing the moisture content of the green malt, the resultant kilned malt can be stored for long periods of time. At 44% moisture the green malt would not store safely for more than a few days. Distilling malt will be kilned to achieve a moisture of 4 - 6% and at these levels it may be stored for several years if need be, although generally it will be used after between 2-10 weeks storage, when it will perform at its best.

During kilning the green malt will develop sweet biscuit flavours that replace the raw, starchy, wet grain aromas that existed prior to kilning. In addition, if peat is burned during kilning and the peat smoke passed through the drying malt, the malt will take on the pealed, smokey, medicinal and seaweed flavours so characteristic of the Islay malt whiskies.

At Port Ellen there are 3 kilns, each hold the contents of I drum which is 5I tonnes original barley weight. The kilns are large circular buildings with perforated steel floors. Warm air is blown underneath the floor, up through the perforated steel plates and through the grain, heating and drying it.

It is important to control the temperature of the grain accurately during kilning as the natural enzymes within the grain are easily damaged if overheated while moist. If these enzymes are damaged the distiller will find it difficult to make good quality (and quantity of) whisky from the malt. In order to give good temperature control the main heat source for the kilns at Port Ellen is from oil fuelled burners which operate under computer control. These provide excellent temperature control and contribute significantly to the high quality of malt that can be produced. The "hot" air added to the kiln will start at a temperature of around 50oc and increase progressively after the "break" (the point where the water on the outside of the grain has been dried off). At the end of kilning the temperature of the air leaving the kiln will be around 70oc.

Peat is also burned for the kilns at Port Ellen. Each kiln has an associated peat fire which is used to produce the peat "reek" (smoke) that gives the malt its flavour.

The setting and tending of this peat fire is the real secret of the Port Ellen Makings. It is important that the fire produces copious quantities of smoke and the quality of the smoke too is important.

The peat used plays a major part in determining the smoke quality. Islay is fortunate in possessing not only large reserves of peat, but also peat of the finest quality. Peat is formed from dead vegetation that is changed by time and the special chemistry of the land into a fuel. New vegetation is continually adding to the existing peat layers and approximately I mm of peat is laid down each year. Parts of the peat moss on Islay are 10 metres deep, indicating that the bottom layer may be of the order of 10,000 years old.

When the peat is cut it is very soft and wet but is soon forms a crust and, after a few weeks it will have shrunk and dried to a hard easily handled solid. During drying and handling small pieces will break off the peat blocks forming what is known as peat caff.

Peat for Port Ellen is cut from Castlehill moss. Castlehill is overlooked by the hills where the lochs supplying the makings with water are situated. The peat and caff are delivered to the maltings where we store over 2000 tonnes, sufficient for I year's production of malt.

The peat smoke is absorbed easily by the green malt when it is still wet so the peat fire is burned from when kilning starts until the point known as the "break" when all the surface moisture has been dried from the malt. The fire will be set using both peat and caff. The object is to produce only good quality smoke from the fire with no visible flame. Too little caff on the fire or too shallow a depth of peat in the fire and it will burn hot, producing only small quantities of poor quality smoke. Too much caff or too much peat on the fire and the fire may not even burn.
The skill of the maltsters is in setting the fire just right, taking into account all the various influencing factors, the quality of the peat, its moisture level, the air flow to the kiln, etc. Every maltster at Port Ellen sets the fire to his own best judgement and there is a friendly rivalry to produce the "best peated" batches of malt.

After the "break" when the majority of the moisture has been driven off the green malt, the temperature of the grain rises and kilning is completed only a few hours later. A typical 43 tonne batch takes around 30 hours to fully kiln.


The malt is removed from the kiln and passed to a "malt in culm" bin from which it is fed to a "dresser" which removes the rootlets from the grain. The rootlets contribute nothing positive to the distiller, who does not wish them included in the malt he pays for. They are removed and mixed with dust taken from incoming barley to form a mixture known as malt residuals. These malt residuals are dampened with water and molasses (to make them more palatable) then passed through a high pressure die to form pellets that are sold off as cattle feed.

The dressed malt is placed in a storage silo. Analysis carried out on samples from the silo will be used to confirm that the malt fully complies with our customers' specifications.

The malt will be "rested" in the silo for a few weeks before delivery to the distillery. Rested malt processes more easily than freshly kilned malt.


Written by John A Thomson


The text is an excerpt from "Port Ellen: Distillery and Maltings" (pp. 12 - 20), written by John A Thomson, published 2010 by Diageo Plc.