Editing Pot still (section)

== Method of operation ==

During first distillation, the pot still (or "wash still") is filled about two-thirds full of a fermented liquid (or [[Wash (distilling)|wash]]) with an alcohol content of about 7–12%.<ref>{{Cite web|url=http://www.pediacognac.com/en/weinbereitungvinificationvinification/merkamale-des-weinscharacteristics-of-the-winecaracteristiques-du-vin/|title=Characteristics of the Wine|website=L'encyclopédie du Cognac|publisher=Bureau National Interprofessionnel du Cognac Entreprise|access-date=22 January 2017}}</ref><ref name=":1">{{Cite book|title=A Glass Apart: Single Pot Still Whiskey|last=O'Connor|first=Fionnán|publisher=Images Publishing|year=2015|isbn=1864705493|location=Victoria, Australia|pages=33}}</ref><ref name=":2">{{Cite book|first1=Graham|last1=Stewart|first2=Inge|last2=Russel|title=Whisky: Technology, Production and Marketing|publisher=Elsevier|year=2014|isbn=0124046037|pages=10-12}}</ref> In the case of whisky distillation, the liquid used is a beer, while in the case of brandy production, it is a [[base wine]]. The pot still is then heated so that the liquid boils. 

The liquid being distilled is a mixture of mainly water and alcohol, along with smaller amounts of other by-products of fermentation (called [[Congener (alcohol)|congeners]]), such as aldehydes and esters.<ref name=":1" /> At [[Standard atmosphere (unit)|sea level]], alcohol ([[ethanol]]) has a normal boiling point of {{convert|78.4|C}} while pure water boils at {{convert|100|C}}.<ref name=":3">{{Cite book|first1=Bill |last1=Owens |first2=Alan |last2=Dikty |first3=Fritz |last3=Maytag |title=The Art of Distilling Whiskey and Other Spirits: An Enthusiast's Guide to the Artisan Distilling of Potent Potables |publisher=Quarry Books|year=2011|isbn=1616735554}}</ref> As alcohol has a lower boiling point, it is more volatile and evaporates at a higher rate than water. Hence the concentration of alcohol in the vapour phase above the liquid is higher than in the liquid itself.

During distillation, this vapour travels up the ''swan neck'' at the top of the pot still and down the ''lyne arm'', after which it travels through ''the condenser'' (also known as the ''worm''), where it is cooled to yield a [[Distillation|distillate]] with a higher concentration of alcohol than the original liquid.<ref name=":1" /> After one such stage of distillation, the resulting liquid, called "low wines", has a concentration of about 25–35% alcohol by volume.

These ''low wines'' can be distilled again in a pot still to yield a distillate with a higher concentration of alcohol.<ref name=":2" /> In the case of many [[Irish whiskey|Irish whiskeys]], the spirit is distilled for a third time. However, cognac and most [[single malt Scotch|single malt Scotch whiskies]] are distilled only twice.

A still used for the redistillation of already-distilled products (especially in the United States) is known as a ''doubler''{{snd}} named after its approximate effect on the level of the distillation purity.<ref name=WAdoubler>{{cite web |url=https://www.whiskyadvocate.com/glossary/doubler/ |title=Doubler |work=[[Whisky Advocate]] |access-date=28 March 2022}}</ref><ref name=Crowgey>{{cite book |first=Henry G. |last=Crowgey |date=2008 |publisher=[[University Press of Kentucky]] |place=Lexington, Kentucky |title=Kentucky Bourbon: The Early Years of Whiskeymaking |isbn=978-0-8131-9183-6 |pages=53, 55, 59}}</ref> Distillers from the early 1800s with sufficient resources to operate both a primary still and a separate doubler would typically use a smaller still for the doubler (typically about half the capacity) than for the first distillation.<ref name=Crowgey/><!-- Crowgey describes doubler practices for several operations circa 1800, focusing primarily on Kentucky frontier operation of the late 1700s and early 1800s, although he includes a quoted 1808 advertisement for a European-made equipment set consisting of two "singling stills" and a doubler. In that particular advertisement, the "singling stills" are 165 gallons each and the doubler has a 75 gallon capacity. That is only one of several described similar couplings of size ratios, mostly showing about half-size capacity for doublers. -->

An alternative way to reach an increased distillation purity without a full second stage of distillation is to put another pot (often a passive pot{{snd}} i.e., without an external heat source) between the pot still and the cooling worm. Such a pot is known as a ''thumper''{{snd}} named after the sound made by the vapour as it bubbles through a pool of liquid in the thumper.<ref name=WAthumper>{{cite web |url=https://www.whiskyadvocate.com/glossary/thumper/ |title=Thumper |work=[[Whisky Advocate]] |access-date=28 March 2022}}</ref> The distinction between a thumper and a doubler is that a thumper receives its input as a vapour prior to cooling, while the intake of a doubler is an already-condensed liquid.<ref name=WAdoubler/><ref name=WAthumper/>

During distillation, the initial and final portions of spirit which condense (with the first portions termed the ''foreshots'' and ''heads'' and the final parts called the ''tails'' and ''feints'') may be captured separately from that in the centre or "heart" of the distillation and may be discarded. This is because these portions of the distillate may contain high concentrations of [[Congener (alcohol)|congeners]] (which it may be desirable to keep out of the final distillate for reasons of style, taste and toxicity). For example, the presence of [[pectin]] in the wash (e.g., due to using a [[Mashing|mash]] made from fruit) may result in the production of [[methanol]] (a.k.a. wood alcohol), which has a lower boiling point than ethanol and thus would be more concentrated in the foreshots. [[Methanol toxicity|Methanol is toxic]] and at sufficient concentrations, it can cause blindness and fatal kidney failure. It is especially important to discard the initial foreshots, while a small amount of the near-centre heads and tails are often included in the final product for their effect on the flavour.<ref>{{cite web |url=https://diydistilling.com/how-to-avoid-methanol-when-distilling/ |title=How to Avoid Methanol When Distilling Alcohol (Must Read!) |website=DIY Distilling |access-date=29 March 2022}}</ref><ref>{{cite web |url=https://www.acsh.org/news/2017/06/06/throw-away-first-cut-popcorn-sutton-chemistry-moonshine-11386 |title=Throw Away The First Cut: Popcorn Sutton & The Chemistry Of Moonshine |work=American Council on Science and Health |first=Josh |last=Bloom |date=6 June 2017 |access-date=29 March 2022}}</ref>