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Do the mash

At its most basic, the process of mashing involves mixing ground malt – known as grist – with hot water to convert the starch within the grain into fermentable sugars The end-product of mashing is called wort. Gavin D Smith explains what’s going on during the mashing process, and how different approaches can influence a distillery’s spirit character


Mashing is part of the ‘brewing’ process of whisky production, and many of the terms used, such as ‘liquor’ for water and ‘sparging’ (see below) are common to beer-making as well as whisky distillation.

The mash tun in which the process takes place is now usually made of stainless steel, although some distilleries such as Glenglassaugh and GlenDronach retain cast-iron mash tuns. Most are closed, but Springbank operates an open mash tun, as do Bruichladdich and Deanston.

Within a traditional mash tun a geared arm projects from a central poll, with projecting rakes on the arm stirring the mash as the arm rotates. Since the 1970s, however, ‘lauter’ and ‘semi-lauter’ tuns have been installed in many distilleries, with the name deriving from the German word ‘lautern’, meaning to filter or purify.

In a lauter tun, the rotating arm remains above the level of the mash and a series of rods project from it to the tun floor, each equipped with a number of blades. A semi-lauter tun continues to use a series of infusions, while a full lauter tun is capable of carrying out mashing in one phase. The advantages of lauter or semi-lauter tuns is they extract more fermentable material from any given quantity of grist.

In the mash tun, the grist is mixed with a charge of water heated to 64°C, a temperature high enough to dissolve sugars but sufficiently low to allow enzymes to continue the processes that started during germination.

After a period of up to an hour, the ‘wort’ is drained from the tun into an underback, and water heated to around 80°C is added to the vessel in order to dissolve more of the sugar. The liquid is drained to the underback where it is combined with the first run-off of wort. This is ready for transfer to washbacks in the distillery tun room.

A final charge of water, known as sparge and with a temperature of approximately 85°C, is then pumped into the mash tun to dissolve any remaining sugar, and this becomes the first charge of water for the next batch of grist. The remaining residue in the mash tun – known as draff – is cleaned out, and traditionally had a useful and ecologically sound role as cattle food, though today it is also used in anaerobic digestion and the creation of bio-energy.

The way in which mashing is conducted has a major bearing on the character of spirit ultimately produced. If clear wort is created then this is likely to lead to fruity, ester-forward spirit, while cloudy wort, containing in suspension barley husks and flour particles, gives a nuttier, more malty and spicy spirit with an oily texture. Clear wort is more likely to be created in a semi-lauter or lauter tun, where the filtration process is more efficient, while cloudy wort can be generated by slower rake revolutions in the tun.

ABOVE: Holyrood distillery has focussed on its mashing process in its annual Cask Programme, with varying wort recipes

Last year, Edinburgh’s Holyrood distillery chose to focus on the mashing process in its annual Cask Programme, offering purchasers spirit made with either clear wort or cloudy wort. According to distillery manager Calum Rae: “We have produced numerous clear wort recipes and have really enjoyed their light and bright character. In contrast to producing a cloudy wort, clear wort requires longer rest times and increased rates of wort recirculation to maximise its clarity.”

When it comes to cloudy wort, Calum says: “The key in producing texture is ensuring our mash tun rakes continue to spin during mashing, to increase the extraction of cereal particles. This is coupled with a very short vorlauf, which is part of the mashing process, used to separate residual particles from the mash. By shortening the vorlauf process we retain more cereal particles, key in producing a sticky, velvety mouthfeel, and nutty flavours.”

As distillers seek to achieve environmental goals, the mashing process inevitably comes under the spotlight, and Diageo has been trialling ‘high gravity’ mashes at Lagavulin and Talisker, while a number of other Scotch whisky distilleries also use the technique. At Lagavulin, the mash size was increased from 4.4 tonnes to 5.4 tonnes, and at Talisker from 8 to 8.75 tonnes and even in excess of 9 tonnes. This means using more malt compared to heated water, requiring less energy to heat a smaller volume of water, while the yield is also increased. High gravity mashes are of particular benefit to distilleries such as Pulteney in Wick, which may find themselves short of process water at times.

Finally, it is worth noting that not all mashing in whisky distilleries is carried out using a mash tun. Teaninich and InchDairnie are two Scottish distilleries equipped with mash filters, more common in the brewing industry.

ABOVE: Inchdarnie’s Ian Palmer explains the workings of its mash filter to Unfiltered editor, Richard Goslan

According to InchDairnie’s website: “At InchDairnie distillery, a mash filter is part of our DNA. Inside it, membranes can squeeze the sugary liquid through filters resulting in a higher yield (more efficient) and crucially more flavour extraction for greater complexity. As such, InchDairnie distillery has high gravity wort, meaning the sugar water is more concentrated than normal – which translates into, when time comes to fermentation, more flavour compounds, esters, are created.

“In addition, the mash filter can handle many types of grain, which would clog a standard mash tun, thus allowing for innovation. Rye being one of them.”

The next stage of malt whisky production involves fermenting the wort, and it is at this point that alcohol is created for the first time. As we shall see next month, just as with mashing, the prevailing fermentation regime can have a significant effect on ultimate spirit character.

ABOVE: Raasay distillery’s draff feeds the local livestock

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