To many, the sight of a burnished, shiny collection of copper pot stills is one the sums up Scotch whisky. Yet why copper? It may appeal aesthetically, yet what room the practical reasons for its continued use in distilleries old and new? Let’s listen what the Whisky Professor needs to say top top the subject.
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Precious metal: Copper is an ext than simply a quite face, states the Whisky Professor
Dear mrs von Trapp
How, indeed, carry out you deal with a problem like Maria’s?
First that all, stills weren’t always made native copper. The earliest instances would have used everything durable and also malleable material came to hand, such together ceramics or glass.
But copper was soon fixed upon together the ideal product with which come manufacture pot stills. That is relatively easy to mould and shape into whatever kind you wish; that conducts warm easily and also efficiently; and also it is resistant to corrosion.
Nonetheless, that does stay out and it is expensive, prompting distillers come experiment – together you imply – through newer, cheaper and an ext durable materials, such as stainless steel. This occurred particularly, however by no means exclusively, in the unified States.
However, early adopters the stainless steel quickly noticed a dramatic readjust in spirit high quality – one unwelcome, sulphurous odour that had actually nothing to do with cut points or the speed at i beg your pardon the stills were run.
Distillers had arrived in ~ copper together the appropriate still material by a procedure of trial and also error; currently they uncovered a hidden benefit of the metal by the very same method, a benefit confirmed by more investigation and experimentation.
Think the copper together a ‘silent contributor’ to soul quality; the ease of access of clean copper within the still is an essential to allow facility chemical reactions to take place, removing very volatile sulphur compound – chief among them dimethyl trisulphide or DMTS – and also helping in the development of esters, which have tendency to provide the heart a fruity character.
This process is also absolutely an essential when making grain whiskies in pillar or continuous stills, whereby copper may be offered in the to produce of the sides of the stills or the bowl themselves. Here, copper go its ideal work in the rectification system, wherein the undesirable compounds are mainly concentrated.
But copper’s prominence extends past the stills us to the apparatus provided to condensation the distilled soul vapour. In malt whisky distilleries, this are generally of two species – shell-and-tube or worm tubs – and both usage copper.
Available copper: Shell-and-tube condensers tend to produce lighter spirit
Worm tubs consists copper coils submerged in tubs of cooling water, yet the shell-and-tube construction has much much more ‘available’ copper, meaning more copper call with the condensing spirit and also producing typically lighter, fruitier and grassier flavours in the tires whisky.
By contrast, worm tubs have tendency to yield more sulphury, meaty or vegetal notes, simply due to the fact that the copper has had less opportunity to react and remove those flavours. Deposits will additionally gradually construct up top top the within of the ‘worm’, reduce the copper’s reactivity further.
Although the remove of this volatile sulphur compounds is generally desirable during the distillation process, the extent to i beg your pardon it wake up – administer by a range of components from quiet shape and size through to method of condensation – is additionally a stylistic decision.
You desire a funky, meaty, contempt sulphury new make? climate you require a distillation procedure that entails less copper contact (and worm tubs). Trying to find fruity, grassy spirit? do the many of every inch of copper in her stills and fit shell-and-tube condensers.
Taking this stylistic an option a phase further, part distilleries are currently fitting stainless steel condensers – Ailsa Bay, for example – to provide them an choice that has less copper contact and also a various style of whisky together a result.
There are two further results of the facility reactions that take place when spirit and also copper interact. The an initial is that, as the reactions take it place, the heart ‘picks up’ copper in a dissolve form.
Only very small amounts the this will certainly be present in the final product (you’ll be relieved to hear); many of it is discharged lengthy beforehand, incidentally posing an environmental an obstacle to distilleries. The blue stuff you see in the spirit safe? Copper salt or, more accurately, copper carbonate.
Blue stuff: Copper carbonate deposits in Lagavulin’s soul safe
The other impact is that, in certain parts of the still where more of the helpful catalytic reactions occur – above the boiling line, in the shoulder, swan neck, lyne arm, condenser and at the start of the worm – the copper will slowly erode.
As the copper thins, the is not unknown because that a still to ‘pant’ choose an over-exerted dog, the shoulders rising and also falling under the strain. Repair or replacement needs to take place swiftly to avoid a collapse.
To sum up, although expensive, copper has great properties that malleability, heat conductivity and also resistance come corrosion. Its can be fried weakness – that, specifically in particular places, it wears out – is likewise one of its biggest strengths, since it is by this copper ‘sacrifice’ the the soul that will end up being whisky is refined and also stripped of undesirable odours and also flavours.
No wonder, then, the distillers will sometimes refer come the existence of what they speak to ‘sacrificial’ copper in constant or stainless stole stills: copper mounted not because of aesthetics or distillation efficiency, however for reasons of soul quality.
In various other words, copper is much, much an ext than just a pretty face. Ns hope the answers your question.
So long, farewell, auf wiedersehen, an excellent night.
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