Islay whisky making
Distilling on Islay Distillation
Distillation is the concentration of the alcohol in the wash by evaporation and selective condensation. In short, the wash is boiled in a still and turns into vapour; the vapour is collected, turned back into liquid and a proportion of it reserved. As alcohol boils at a lower temperature than water, careful control of the temperature and collection of the condensed vapour will give a concentrated spirit containing desirable alcohol and flavour compounds. This spirit is the liquid that will one day become whisky.
Malt whisky, by law, uses a batch distillation process, and all of the distilleries on Islay use double distillation to create their spirit – this means that the wort is distilled to create an intermediate ‘low wine’, which is further distilled to produce the final spirit.
Malt whisky stills are, also by law, copper vessels. They are usually pot shaped with a thin and comparatively tall neck – known as a ‘swan neck’ – ending in an angled turn into a pipe called a lyne arm. This is connected to a condenser that will cool the hot vapour from the still, turning it back into liquid ready for collection.
The liquid produced from the stills is directed into receiving vessels via a spirit safe. This is traditionally a locked box which all low wines and spirit passes through. Locks were put in place to ensure that alcohol wasn’t siphoned off during the distillation process to avoid duty before the amount of spirit could be measured, and the keys were held by the local excise official. The safe allows the still operator to direct the flow of condensed liquid from the still between various receivers as well as test its strength, all without having direct access to it.
FACT: Laphroaig is the only distillery on Islay with an odd number of stills
FACT: All distilleries on Islay use shell and tube condensers
The distillation processes starts with the charging of the first still – usually called the ‘wash still’ – with wash. As the still is heated, various compounds will begin to vaporise and travel up the neck of the still. Both through interaction with the copper of the still and due to the temperature of the upper reaches of the still, the vapours will condense and drop back into body of the still in a process known as reflux. Lighter vapours will make their way to the top of the still, into the lyne arm and from there into the condenser. There the vapour is cooled, returning it to liquid form, and passed through the spirit safe into the low wines receiver where it is reserved for the second distillation. The ABV of the distilled liquid starts at about 45% ABV and drops throughout distillation, with everything above about 1% ABV collected to give a low wine of about 25% ABV.
The liquid left in the still – pot ale – is disposed of. On Islay it is pumped directly into the sea, but on the mainland it is often concentrated into a syrup or mixed with draff to create dark grains, both used as cattle feed.
The second distillation happens in a very similar way to the first, but the resulting liquid is separated into three ‘cuts’: heads/foreshots, heart and tails. The heart cut is reserved, and the heads and tails are mixed with low wines and redistilled. The heart cut varies between distilleries, but is usually lies between 60% ABV and 75% ABV. The heads are full of lighter compounds that vaporise easily, while the tails are heavier, including undesirable fusel oils, so the selection of the heart cut will have a significant effect on the final character of the spirit.
Copper is not only a good conductor of heat, making it an excellent material for building stills and condensors, but it also interacts with the vapour allowing for a ‘conversation’ which strips heavier compounds, including sulphur, leading to a lighter spirit. This happens both in the still, where careful running of the still to give an appropriate amount of reflux will help increase the amount of interaction to an appropriate level, and in the condensers.
There are two main types of condenser used when making single malt whisky: worm tubs, and shell and tube. A worm tub consists of a long coil of tapering copper tube sat in a tub of water – vapour enters at the top and travels down the tube, cooling as it does, coming out as liquid at the end. Shell and tube condensers consist of a large tube – the shell – containing a number of smaller copper tubes. Vapour is directed into the shell and water is run through the tubes; as the vapour hits the tubes it condenses, running down to the bottom of the shell, where it is collected. Management of the temperature of the water in both types of condenser will speed up or slow down the condensation process, varying the amount of interaction the vapour will have with the copper, producing a lighter or weightier spirit as desired.
Once the heart cut has been collected, it is now referred to as new make spirit and is ready to be filled into cask and aged.Next > Casks