Still very important

Still very important

Ian Wisniewski explains how differing still designs influence the style and flavour of whisky

Production | 16 Nov 2001 | Issue 19 | By Ian Wisniewski

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Knowing that stills of a certain size and shape yield spirit with a particular flavour profile is all very well, but applying this knowledge the other way around is far more challenging. In fact, designing stills in order to produce a spirit with specific
characteristics is merely a starting point, as this is only one factor in a complex (and not always fully understood) equation, which also includes the spirit cut, heating method, rate of distillation and type of condenser.Even the relationship between the wash and spirit stills is difficult to quantify beyond stating that new make spirit is shaped by wash stills and refined by spirit stills. But if the low wines aren’t right, the spirit stills can’t correct them (and if fermentation is mismanaged, distillation can’t fix that either). Although wash and spirit stills can be twinned and constructed to the same ‘tech spec’, numerous distilleries have a medley of variously shaped stills (an historic legacy of course, not a strategic master plan). In fact, Mortlach has such an individual line-up that every wash and spirit still differs from all its neighbours.As the degree of reflux (condensation) is a key factor in establishing the profile of the spirit, the length of the neck is an important consideration. The taller the still, the greater the degree of reflux. This is because heavier, denser, oilier flavour compounds have a higher boiling point than lighter flavour compounds and as they rise up the still the temperature becomes relatively cooler, which means they condense and return to the boil pot (base). An ultimate in the industry are Glenmorangie’s stills (vital statistics being 5.13 metres tall, or 16 feet and 101/4 inches for imperialists), promoting light, floral, fragrant new make spirit with a sweet edge. As a shorter neck means less temperature variation, there is consequently less reflux. This promotes the progress of heavier flavour compounds into the condenser, yielding fuller-bodied spirit, with a creamier, earthier, oilier texture.
But size doesn’t always matter, as reflux can also be enhanced by customising stills with various matching accessories, including a boil bowl, pinched waist or flat top, while cooling the neck of the still is another option. A traditional (cynical) explanation for a flat topped still has been the low ceiling it had to squeeze under. However, the technical influence of a flat top, as at Cragganmore, results in a slightly higher degree of reflux because the progress of vapours is not as gradual or progressive as it is with a swan neck.A pinched waist (as though a corset had been tightened around the still), can be seen in The Glenlivet’s wash and spirit stills. By reducing the surface area available to the vapours (by about two-thirds at The Glenlivet), a pinched waist initially accelerates the progress of vapours into the neck. The subsequent, sudden widening of the neck, and relatively cooler temperature, consequently increases reflux. A boil bowl (bulbous section between the boil pot and neck) can vary from being mildly to acutely convex (the more convex, the more reflux). When vapours carrying heavier flavour compounds expand into this larger, relatively cooler area, they condense and return to the boil pot.Dalmore Distillery effectively doubles up by having a cooling jacket (also known as a water jacket) between the boil bowl and neck of the spirit still through which cold water circulates (using the same water source as for the condenser). This practise dates from 1839, with the oldest jacket still in active service dating from 1874. At Fettercairn a different approach yields a similar result. From a circular pipe located at the top of the spirit still, cold water runs along the neck and collects in a trough fitted around the still (from which it also drains). This has the effect of “giving the vapours inside a little fright” according to Distillery Manager Willie Tait. His more technical explanation is that cooling a fairly short neck gives it the effect of being much taller. While purifiers are rarely seen, this is a feature of Glen Grant’s wash and spirit stills. As vapours leave the still and enter a copper pipe in a tank cooled by water, lighter elements within the vapour continue onto the condenser while heavier elements return to the still via another pipe. Without this proceedure Glen Grant’s new make spirit would be oilier and heavier, says Chivas Brothers’ Brand Ambassador Jim Cryle. Similarly, in the opinion of Site Manager John Reid, a purifier in the spirit still increases the buttery, creamy notes of Edradour’s new make spirit. But just as important as design features that make a still unique, is the manner in which the still is employed. Pungent, fruity esters are more evident in spirit collected between 68 and 72% abv, while a spirit cut extending to around 58% abv includes heavier, oilier, fatty acids. Consequently, altering or separating the spirit cut into batches collected at different strengths would enable varying styles of whisky to be produced from the same still. How to heat the still provides another lively forum. Steam heating, which replaced many gas and coal fires in the 1960s and 70s, is typically considered the most controllable. While some distilleries maintain that changing the heating method had no discernible impact on the spirit, others are totally anti-change. At The Glenfarclas Distillery an experiment conducted in 1981 was considered definitive. John Grant, Chairman of J&G Grant, stated that using steam coils to produce a trial batch of new make spirit “took the body and guts out of it” and that “all the character went”. In addition to the method of heating, how this is utilised also affects the degree of reflux. Heating the still more rapidly increases the rate of distillation, driving off vapours more readily. As this reduces the degree of reflux, it promotes a higher proportion of heavier flavour compounds. Driving vapours more rapidly also entails the risk of carrying over some undistilled liquid, showing as a sour note in new make spirit. Correspondingly, a lower temperature means a slower rate of distillation, more reflux and a lighter (some say finer) spirit. At the leisurely end of the scale this means collecting around nine litres of spirit per minute, compared to around 20 litres per minute in the fast lane. Additional reflux can also be prompted en route to the condenser, using a lye pipe (or lyne arm) extending at an incline, which drives heavier flavour compounds back into the still. By providing a greater surface area than a typical worm, a modern ‘shell and tube’ condenser increases the degree of contact between the spirit and copper, helping to strip out meaty, sulphurous compounds. However, worms (a coiled copper pipe of decreasing diameter, set in a worm tub with cold water) do not neccessarily result in a higher level of sulphurous, meaty flavours and the challenge lies in controlling the level of these characteristics to achieve a complex whisky. Replacing stills with identikit duplicates is another routine factor, though tales of minor dents being hammered on to the same spot of a replacement are essentially a case of whisky folklore. “It’s been shown that small dents don’t have any influence,” says Richard Forsyth of still supremos Forsyths. Similarly, requesting a ‘rivet finish’ instead of welding is down to aesthetics rather than any effect on the spirit. “There’s no difference between a riveted or welded still, but welding is cheaper, quicker and more pliable for beating into shape,” says Richard Forsyth. The neck of a wash still is typically replaced every eight to 10 years, with the pot lasting up to 25 years. The boil pot of a spirit still may last 10 to 12 years, and the neck 25 to 30 years, according to Richard Forsyth. “The copper needs to be replaced when it reaches less than half its original thickness, with the standard thickness around four to five millimetres. A steam heated boil pot is around six millimetres, while a direct fire boil pot requires around 12 to 16 millimetres, while also having a shorter life cycle than a steam heated boil pot,” he adds. Using a new still also entails some introductory distillation runs to season it and an initial yield of spirit shows a higher copper content, as a coating needs to
accumulate on the interior of the stills. So, knowing these principles, is it possible to quantify the importance of the stills within the production cycle? Well not easily, that’s for sure. Beyond the usual 60% of the malt’s eventual flavour being attributed to maturation, I’ll leave dissecting the balance to an expert. “Less than 10% is accounted for by the barrel’s previous incumbent, then maybe 5% is influenced by the barley variety, and 5% by the strain of yeast,” says David Robertson, The Macallan’s Master Distiller. Then the crucial bit. “10% could be the wash still and 10% the spirit still, with the influence of the spirit still being divided into 5% each for the size and shape of the still and 5% for the spirit cut.” Sounds good to me.
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