Editing Tequila (section)

== Chemistry ==

=== Alcohol content ===
[[File:S cerevisiae under DIC microscopy.jpg|thumb|''[[Saccharomyces cerevisiae]]'', under a microscope]]
Tequila must have between 35% and 55% alcohol content (70 and 110 U.S. proof).<ref name="tequila.net">{{cite web | url = http://www.tequila.net/faqs/tequila/what-are-the-regulations-governing-tequila.html#chapter6 | title = Official Mexican Standard for Tequila | access-date = 2010-07-13 | archive-date = 2013-10-30 | archive-url = https://web.archive.org/web/20131030034521/http://www.tequila.net/faqs/tequila/what-are-the-regulations-governing-tequila.html#chapter6 | url-status = live }}</ref> Tequila is a distilled beverage that is made from the fermentation of the sugars in the blue agave plant once it has been cooked, the main sugar being fructose.<ref name="Pinal">{{Cite journal|last1=Pinal|first1=Leticia|last2=Cedeño|first2=Miguel|last3=Gutiérrez|first3=Humberto|last4=Alvarez-Jacobs|first4=Jaime|date=1997-01-01|title=Fermentation parameters influencing higher alcohol production in the tequila process|journal=Biotechnology Letters|language=en|volume=19|issue=1|pages=45–47|doi=10.1023/A:1018362919846|s2cid=40739267|issn=0141-5492}}</ref> Through the fermentation process, many factors influence the higher-order alcohols present in tequila, which include molecules such as [[Isobutanol|isobutyl alcohol]] and [[isoamyl alcohol]], along with the [[ethanol]].<ref name="Pinal" /> Factors include the strain of yeast, the age of the agave plant itself, temperature, and the ratio of carbon to nitrogen.

The yeast strain used and the carbon-to-nitrogen ratio have the biggest influence on the production of higher-order alcohols; this is not surprising, as production of ethanol and higher-order alcohols is an intrinsic property of the metabolism of each strain.<ref name="Pinal" /> The type of yeast most commonly found in tequila is ''[[Saccharomyces cerevisiae]]'', which can include many different strains. For example, ''CF1 agaves'', a type of yeast, produces much more ethanol than a CF2 strain, as the two yeasts' metabolic mechanisms differ.<ref name="Pinal" /> Prevalence of certain strains of yeast may be influenced by agricultural practices. It was found that higher ratios of carbon to nitrogen resulted in greater production of higher-order alcohols such as isobutyl alcohol and isoamyl alcohol. The lower level of nitrogen in the fermentation process results in deamination reactions of [[amino acid]]s, which in turn leads to the synthesis of higher alcohols.<ref name="Pinal" /> The [[Ehrlich pathway]] refers to this process in which alpha-keto acids are decarboxylated and transformed to aldehydes and to higher alcohols.

The temperature of the fermentation process also greatly affects the alcohol content of the resulting product. For example, a study conducted by Pinal ''et al.'' found that cultivating two strains at a temperature of 35&nbsp;°C as compared to a temperature of 30&nbsp;°C produced more isoamyl alcohol. The higher temperature appears to be favorable for the action of the yeast.<ref name="Pinal" />

The age of the agave plant is also a factor: the older the plant, the greater the production of higher-order alcohols. It was shown in a study that the concentration of amyl alcohol increased by 30% as the plant aged. Conversely, a higher concentration of methanol is found when using younger plants. This change may be due to differences in agricultural practices with plants of different ages.

=== Color ===
[[File:Tequila Silver, Reposado, and Anejo.jpg|thumb|right|White (left), reposado (centre) and añejo (right) tequila, showing the difference in color]]
Tequila's color ranges from clear to a brownish amber, depending on the aging process and the type of wood used for storage.<ref name=":2">{{Cite web|url=http://www.scocia.com/newsite/Tequila.pdf.pdf|title=Tequila|access-date=2016-03-23|archive-date=2016-04-08|archive-url=https://web.archive.org/web/20160408003535/http://www.scocia.com/newsite/Tequila.pdf.pdf|url-status=live}}</ref> The white (blanco) version of tequila, also nicknamed "silver", is the product with no aging, or may be aged less than two months. It is the purest form, as little has been done to change it. What is known as gold, joven or oro tequila is usually white tequila with the addition of grain alcohols and caramel color;<ref name=":2" /> some higher-end gold tequilas may be a blend of white and reposado. Rested (reposado) tequila is aged for a relatively short time (two months or more), and aged (añejo) tequila for a longer time (a year or more). All aging of tequila is done in wooden containers.<ref name=":2" /> The aging process can last three years or more, and can create or enhance flavors and aromas. It generally imparts a golden color.<ref name=":2" />

=== Flavor and aroma ===
[[File:Venta_de_tequila_en_Tequila_Jalisco_México..JPG|thumb|right|Tequila store in Jalisco]]
There are more than 300 known compounds in tequila, many of which are produced during the fermentation process, the raw material used, and to a lesser degree during the maturation.<ref name=":3">{{Cite book|url=https://books.google.com/books?id=O-t9BAAAQBAJ&q=vanillin%2520in%2520agave%2520plant&pg=RA4-PA286|title=Encyclopedia of Food and Health|date=2015-08-26|publisher=Academic Press|isbn=9780123849533|language=en}}</ref> The components that make up tequila do not act individually to give tequila its distinctive flavor and aroma, but rather, depend on the interaction and quantity of each volatile compound.{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}}  The volatile compounds responsible for the flavor and aroma profiles of the tequila are put into a category called [[organoleptic]] compounds and are known to increase in concentration with a slower fermentation process.<ref name=":5">{{Cite web|url=https://www.researchgate.net/publication/286621161|title=Production of tequila from agave: historical influences and contemporary processes|website=ResearchGate|access-date=2016-03-19}}</ref> The organoleptic compounds produced during fermentation include higher order alcohols, [[methanol]], [[ester]]s, [[carbonyl]]s, [[terpene]]s, and [[furan]]s.{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}}

Higher-order alcohols have a strong aroma, and the quantity present in each tequila depends on the carbon:nitrogen ratio and temperature during the cooking and fermentation processes.<ref name=":5" /> Some of the most common alcohols present other than [[ethanol]] are: [[isoamyl alcohol]], [[isobutanol]], and [[1-Propanol|1-propanol]].{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}}  Methanol is thought to be mainly generated through hydrolysis of methylated [[pectin]], which is naturally present in the agave plant, but there has been speculation that it is also partly produced from the enzymatic reactions of yeast strains containing pectin methyl esterase enzyme, which break up the methoxyl group from the pectin.{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}}  Nearly 50 different esters are identified in tequila, which together give rise to the fruit-like flavors and smell.{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}}  One of the most abundant esters is [[ethyl acetate]], which is synthesized during fermentation by the yeast ''[[Saccharomyces cerevisiae]],'' using alcohol transferase enzyme that links acetic acid to ethanol.{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}}

In general, the longer the controlled fermentation period, the higher yield of esters produced.<ref name=":5" /> During the fermentation process, ethanol is oxidized and one of the main compounds produced are [[acetaldehyde]]s, which adds the flavor necessary for the final product of tequila.{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}}  For example, isovaleraldehyde seems to produce a sweet, cocoa, and chocolate-like flavor. 2 and 3-methylbutanal produce a malty flavor.<ref name="Benn 557–566">{{Cite journal|last1=Benn|first1=Scot M.|last2=Peppard|first2=Terry L.|date=1996-01-01|title=Characterization of Tequila Flavor by Instrumental and Sensory Analysis|journal=Journal of Agricultural and Food Chemistry|volume=44|issue=2|pages=557–566|doi=10.1021/jf9504172|issn=0021-8561}}</ref> The agave plant contains many phenolics such as [[vanillin]] and [[syringaldehyde]]s, which present a strong and fruity or herbal aroma. It also contains [[eugenol]], which can deliver a hint of spicy flavor to the tequila.<ref name=":3" /> Because the production of tequila involves heating, [[Maillard reaction|Maillard browning]] reactions occur, and [[furan]]s are produced during the thermal degradation of sugar.<ref name=":6">{{Cite journal|last1=Rodríguez|first1=David Muñoz|last2=Wrobel|first2=Katarzyna|last3=Wrobel|first3=Kazimierz|date=2005-08-16|title=Determination of aldehydes in tequila by high-performance liquid chromatography with 2,4-dinitrophenylhydrazine derivatization|journal=European Food Research and Technology|language=en|volume=221|issue=6|pages=798–802|doi=10.1007/s00217-005-0038-6|s2cid=95032451|issn=1438-2377}}</ref> The most prominent furanic compounds include [[2-furaldehyde]] and 5-methylfuraldehyde,<ref name=":6" /> which can contribute to the smoky flavor of tequila.<ref name=":5" /> Guaiacol also seems to contribute to Tequila's smoky flavor. Beta-demascenone contributes to the woody, floral taste of tequila.<ref name="Benn 557–566"/>

Volatile compounds that contribute to the overall taste and aroma of tequila can be quantitatively assessed and evaluated by [[gas chromatography]].<ref>{{cite web|url=https://www.researchgate.net/publication/227329176|title=Authentication of Tequila by Gas Chromatography and Stable Isotope Ratio Analyses|first1=Norbert|last1=Christoph|date=August 27, 2003}}</ref> [[Discrimination testing|Discrimination tests]] such as [[Discrimination testing#Duo-trio|duo-trio]] and [[triangle test]]s are also used to evaluate the quality of the tequila.<ref name=":3" />