Editing Whisky (section)

==Chemistry==

===Overview===
Whiskies and other [[distilled beverage]]s, such as [[cognac (drink)|cognac]] and [[rum]], are complex beverages that contain a vast range of [[flavouring]] compounds, of which some 200 to 300 are easily detected by chemical analysis. The flavouring chemicals include "[[carbonyl]] compounds, alcohols, [[carboxylic acid]]s and their [[ester]]s, nitrogen- and sulfur-containing compounds, [[tannin]]s, and other [[natural phenol|polyphenolic]] compounds, [[terpene]]s, and oxygen-containing, [[heterocyclic compound]]s" and esters of [[fatty acids]].<ref>{{Cite book |last=Maarse |first=H. |url=https://books.google.com/books?id=_OvXjhLUz-oC |title=Volatile Compounds in Foods and Beverages |publisher=CRC Press |year=1991 |isbn=978-0-8247-8390-7 |page=548}}</ref> The nitrogen compounds include [[pyridine]]s, [[picoline]]s and [[pyrazine]]s.<ref>{{Cite book |last1=Belitz |first1=Hans-Dieter |url=https://books.google.com/books?id=_QWbLTSL6HoC |title=Food Chemistry |last2=Schieberle |first2=Peter |last3=Grosch |first3=Werner |publisher=[[Springer Science+Business Media|Springer]] |year=2004 |isbn=978-3-540-40818-5 |page=936}}</ref> The sulfur compounds include thiophenes and polysulfides which seem to contribute to whiskey's roasted character.<ref name="Cole 361–385">{{Cite book |last1=Cole |first1=V. C. |title=Fermented Beverage Production |last2=Noble |first2=A. C. |date=1 January 1995 |publisher=Springer US |isbn=9781475752168 |editor-last=Lea |editor-first=A. G. H. |pages=361–385 |language=en |doi=10.1007/978-1-4757-5214-4_14 |editor-last2=Piggott |editor-first2=J. R.}}</ref>

===Flavours from treating the malt===
The distinctive smoky flavour found in various types of whisky, especially Scotch<!--single Islay malts particularly -->, is due to the use of [[peat]] smoke to treat the [[malt]].

===Flavours from distillation===
The flavouring of whisky is partially determined by the presence of [[Congener (alcohol)|congeners]] and [[fusel oil]]s. Fusel oils are higher alcohols than [[ethanol]], are mildly [[toxic]], and have a strong, disagreeable smell and taste. An excess of fusel oils in whisky is considered a defect. A variety of methods are employed in the distillation process to remove unwanted fusel oils.  Traditionally, American distillers focused on secondary filtration using [[charcoal]], [[gravel]], [[sand]], or [[linen]] to remove undesired distillates.

[[Acetal]]s are rapidly formed in distillates and a great many are found in distilled beverages, the most prominent being [[acetaldehyde]] diethyl acetal ([[1,1-diethoxyethane]]). Among whiskies the highest levels are associated with malt whisky.<ref>{{Cite book |last=Maarse |first=H. |url=https://books.google.com/books?id=_OvXjhLUz-oC |title=Volatile Compounds in Foods and Beverages |publisher=CRC Press |year=1991 |isbn=978-0-8247-8390-7 |page=553}}</ref> This acetal is a principal flavour compound in [[sherry]], and contributes fruitiness to the aroma.<ref>{{Cite web |title=June 2007 |url=http://www.beerbrewer.co.uk/2007/06/ |url-status=dead |archive-url=https://web.archive.org/web/20071219120702/https://www.beerbrewer.co.uk/2007/06/ |archive-date=19 December 2007 |access-date=8 December 2007 |publisher=The Beer Brewer}}</ref>

The diketone [[diacetyl]] (2,3-butanedione) has a buttery aroma and is present in almost all distilled beverages. Whiskies and cognacs typically contain more of this than [[vodka]]s, but significantly less than rums or [[brandy|brandies]].<ref>{{Cite book |last=Maarse |first=H. |url=https://books.google.com/books?id=_OvXjhLUz-oC |title=Volatile Compounds in Foods and Beverages |publisher=CRC Press |year=1991 |isbn=978-0-8247-8390-7 |page=554}}</ref>

Polysulfides and thiophenes enter whiskey through the distillation process and contribute to its roasted flavour.<ref name="Cole 361–385" />

===Flavours from oak===
[[File:Oak Barrel.png|thumb|A charred oak barrel used to age whiskey]]
Whisky that has been aged in [[Barrel#Whiskey|oak barrels]] absorbs substances from the wood. One of these is [[cis-3-methyl-4-octanolide]], known as the "whisky [[lactone]]" or "quercus lactone", a compound with a strong [[coconut]] aroma.<ref>{{Cite web |title=Aromas and Flavours |url=http://www.wine-pages.com/guests/tom/taste5.htm |url-status=dead |archive-url=https://web.archive.org/web/20071018025957/http://www.wine-pages.com/guests/tom/taste5.htm |archive-date=18 October 2007 |access-date=8 December 2007 |publisher=Wine-Pages.com}}</ref><ref>{{Cite book |last1=Belitz |first1=Hans-Dieter |url=https://books.google.com/books?id=_QWbLTSL6HoC |title=Food Chemistry |last2=Schieberle |first2=Peter |last3=Grosch |first3=Werner |publisher=[[Springer Science+Business Media|Springer]] |year=2004 |isbn=978-3-540-40818-5 |page=383}}</ref>

Commercially charred oaks are rich in [[natural phenol|phenolic compounds]].<ref>{{Cite web |title=What Is The Chemistry Of Whisky? |url=https://topwhiskies.com/blogs/whisky-blog/what-is-the-chemistry-of-whisky |access-date=2022-07-11 |website=TopWhiskies |language=en}}</ref> One study identified 40 different phenolic compounds. The [[coumarin]] [[scopoletin]] is present in whisky, with the highest level reported in [[Bourbon whiskey]].<ref>{{Cite book |last=Maarse |first=H. |url=https://books.google.com/books?id=_OvXjhLUz-oC |title=Volatile Compounds in Foods and Beverages |publisher=CRC Press |year=1991 |isbn=978-0-8247-8390-7 |page=574}}</ref>

In an experiment, whiskey aged 3 years in [[orbit]] on the [[International Space Station]] tasted and [[High-performance liquid chromatography|measured]] significantly different from similar test subjects in [[gravity]] on Earth. Particularly, wood extractives were more present in the space samples.<ref>{{Cite web |last=Grush |first=Loren |date=10 September 2015 |title=Whiskey aged in space tastes like throat lozenges and rubbery smoke |url=https://www.theverge.com/2015/9/10/9300435/whiskey-space-taste-test-ardbeg-distillery-nanoracks |access-date=24 May 2016 |website=The Verge}}</ref>

===Flavours and colouring from additives===
Depending on the local regulations, additional flavourings and colouring compounds may be added to the whisky. [[Canadian whisky]] may contain caramel and flavouring in addition to the distilled mash spirits. Scotch whisky may contain added [[caramel color|(E150A) caramel colouring]], but no other additives. The addition of flavourings is not allowed in [[American whiskey|American]] "straight" whiskey, but is allowed in American blends.

===Chill filtration===
Whisky is often "[[chill filtering|chill filtered]]": chilled to precipitate out fatty acid esters and then filtered to remove them. Most whiskies are bottled this way, unless specified as ''unchillfiltered'' or ''non-chill filtered''. This is done primarily for cosmetic reasons. Unchillfiltered whiskies often turn cloudy when stored at cool temperatures or when cool water is added to them, and this is perfectly normal.<ref>{{Cite web |title=Chill Filtration |url=http://www.whiskyforeveryone.com/whisky_basics/chill_filtration.html |access-date=21 March 2013 |website=Whiskey Basics |publisher=Whisky for Everyone}}</ref>