Islay whisky making

Distilling on Islay Mashing

Once the malt has been milled, it is mixed with water to extract starch, sugars and other compounds and continue the conversion of starch into fermentable sugars. This stage is known as mashing.

When mashed, the particles of grist absorb water, allowing the compounds within to dissolve. Much of the remaining starch gelatinises, dissolving in the water and becoming an easier target for the enzymes to convert it into fermentable sugars. Controlling the temperature of the mash to balance the efficiency of the various processes at work is key.

The vessel used to combine the grist and water is a mash tun, and there are two main styles still in use. They are all vats with slots in the bottom that can be opened to allow the liquid within to run off, which filters out some of the solids. Traditional mash tuns use large paddles to mix the grain, while lauter tuns have a series of revolving rakes attached to an arm that rotates above the level of liquid in the tun. While seemingly very similar in operation, lauter tuns allow more agitation of the mash, giving an increase in extraction efficiency, which has made them increasingly widespread since their introduction in the 1970s.

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Most distilleries in Scotland still use a process known as batch infusion mashing, where multiple batches of water – each known as a ‘water’ – of differing temperatures are mixed with the grist before being run off and collected separately. Each water is thoroughly mixed with the grist and left to stand before the filtration slots are opened to allow the liquid to drain off. Three or four waters are used, each at a progressively higher temperature. The first will be around 64.5°C, which will extract large amounts of fermentable sugars without overly interfering with enzyme activity, and the second around 70°C, continuing to extract sugars but with more degradation of enzyme activity. These two waters are passed on to the next stage of production. Third and even fourth waters are much hotter, at potentially 80° or 90°C – temperatures that will extract most of the remaining sugars, but at the cost of enzymatic activity. Rather than pass these directly on to the fermentation stage, they are reserved and used as part of the first water in a subsequent mash, ensuring that minimal extractable sugar is lost.

Once mashing has finished, the spent grain – also known as draff – is removed from the mash tun. It is often used as cattle feed, as it is high in protein and fibre, either in its raw form or after processing into pellets.

The waters reserved for production are cooled to around 20°C and combined. The sugary liquid is now called wort.

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