Mash course

Mash course

Ian Wisniewski takes us step by step through the mashing process

Production | 17 Nov 2003 | Issue 35 | By Ian Wisniewski

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With distillation and maturation seen as the key partnership influencing the flavour of malt whisky, it’s easy to dismiss mashing as an ‘industrial equation.’ Starch equals sugar, which in turn equals the yield of alcohol. However, as every stage of the production process plays a vital role in maintaining consistency, any discrepancies during mashing can also have a significant effect on fermentation, and therefore the end result.A prerequisite for successful mashing is milling the barley, with each distillery having an established ‘tech spec.’ Milling is undertaken using two sets of rollers, the first squeezes the grains to ‘pop’ the husk, with the second set grinding the kernels further.This yields three separate grades of malt: husk, grits (also known as middles) which are medium-ground, and the finer-ground fines (or flour). Collectively termed grist, a typical specification is around 20 per cent husk, 70 per cent grits and 10 per cent flour.This ratio provides an ideal total surface area, promoting a maximum rate of conversion from starch to sugar during mashing (when grist is combined with 3-4 batches of progressively hotter water in a mash tun).The proportions of each grade also reflect practical considerations, that balance maximum extraction with good drainage. Husks help water drain through the grist, though too much husk would prevent the grist from mashing properly. Similarly, too high a level of fines could result in an enormous helping of porridge.Needless to say, some distillers describe the water used for mashing as ‘significant,’ particularly if it has permeated through peat. However, it’s the temperature rather than the source of the water that matters during mashing, with the first water and grist combined in a mashing
machine or mixer, and conducted through a spout into the mash tun.The optimum ‘strike temperature,’ literally the temperature at which the first batch of water strikes the grist, is typically 64.5ºC (the water is usually a few degrees higher than the strike temperature, allowing for the inevitable ‘cooling effect’ when it hits the cold grist). The effect of the hot water is to activate diastase (a combination of enzymes created within the barley during malting), which initiates the conversion of starch into fermentable sugars.Achieving an accurate strike temperature is crucial, as a temperature in excess of 65.5ºC can potentially damage or destroy enzymes within the barley. This entails a subsequent risk of not converting all the starches.An option when applying the first water, variously referred to as ‘recycling’ or ‘vorloffing,’ sees the initial liquid that drains through the bottom of the mash tun, being piped back up to the top, and repeating the journey.It’s entirely practical, as this initial liquid contains a relatively low sugar level. Adding a simple accessory like a plate ensures that this recycled water spreads out when it emerges from the pipe, and doesn’t create a ‘hole’ in the grist.Needless to say, mashing schedules vary, with some allowing the first water to drain straightaway, while others let it sit before draining it through perforated plates at the bottom of the mash tun.Some distilleries drain the first water before adding the second. Others begin adding the next batch while there is still a residual amount of the first water, as a lack of residual water could see sticky sugars in the malt compact and cause problems.While the temperature of the first water must be absolutely right, there is a more generous margin for subsequent additions, with the second water around 65-74ºC.This helps flush out stickier sugars and instigate additional enzymatic reactions. Another practical consideration is that the second water can help ‘push through’ any residual first water.The first and second waters yield ‘wort,’ with around 90 per cent of the starches converted in the mash tun. Consequently, unconverted starches draining through within the wort undergo ‘secondary conversion,’ as enzymes in the wort continue working en route to the underback (an intermediary holding vessel), and even within the washback once fermentation has begun.Once sufficient wort has been collected to fill the washbacks, a third water is added at a temperature of around 85-90ºC, or higher, but below boiling point which would damage any remaining enzymes. This third water helps wash out any residual sugars, and is stored in a separate tank from the wort. Known as ‘sparge,’ this is recycled as the first water of the subsequent mashing cycle. Some distilleries also add a fourth water, at around 90-95ºC, which is recycled as the second water.Mash tuns are generally fashioned from stainless steel, though Springbank, Bruichladdich, Caol Ila and Edradour are among the traditionalists using cast iron. Whether this offers any advantages is open to debate, though it’s undoubtedly harder to clean than stainless steel.Some stainless steel mash tuns sport a copper lid, as at Bunnahabhain, Glenfiddich and Auchentoshan. Two practical reasons for adding a copper lid are heat insulation and malleability when shaping the lid. But then again, it can also be a case of sheer aesthetics.Another option is no lid at all, with Bruichladdich and Springbank among the rarities going topless. The consensus is that this doesn’t significantly affect the temperature in the mash tun, and may only require a little more energy to be expended on heating the water.The interior design of a mash tun features a matching accessory either in the form of a rake, which is more historic, or a lauter, which has been used in the industry for the past 20 years.Lauter tuns feature slowly rotating arms that are effectively a series of vertical blades, from which smaller blades protrude horizontally in a staggered format. The effect of a lauter is to gently maximise drainage through the bed (ie. grist and water).A lauter gives the option of raising and lowering the arms, which enables the distiller to choose the height of the bed that is agitated, whereas the arms of a semi-lauter remain fixed.Mash tuns pre-dating ‘lauter-isation’ are still in active service, at distilleries such as Springbank and Bruichladdich, equipped with a rake. This means rotating arms possessing comb-like teeth, that resemble the movement of a swimmer doing front crawl.When using a rake each batch of water is typically ‘stirred in’ a few times. Meanwhile, a lauter gives the option of continual gentle agitation, depending on the speed.At Glenmorangie, for example, one complete rotation on the slowest speed setting takes 14 minutes. Any acceleration would pose a risk of agitating the bed too intensely and creating cloudy wort.While mashing is not generally regarded as significant in influencing the character of new make spirit, wort clarity is an important issue.Clouding can be caused by fines draining through, and being held in suspension within the wort.As fines can affect fermentation and distillation, the resulting character of the malt whisky may also be affected. However distilleries which have traditionally used cloudy wort continue doing this, in order to maintain consistency.Another ‘influence’ on the flavour of the resulting malt whisky is that peating levels decrease during mashing, with a certain level of phenolics lost to the residue grist, referred to as ‘spent grain’ or ‘draff.’This is sold and used as cattle feed, which provides a prime example of recycling.
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