View source for Browning in red wine

{{Short description|Chemical process affecting red wines}}
{{Use dmy dates|date=September 2018}}
[[File:Assessing the age of a red wine.jpg|thumb|191x191px|A wine tasting assessing the age of a red wine by tilting the glass forward and observing the rim variation and change of color against a white surface.]]
[[Redox|Oxidation]] and [[Chemical reduction|reduction]] in [[red wine]]s can lead to a particularly undesirable [[brick red]] color in red wines (or an "orangey" color in [[white wines]]). This process is sometimes referred to as '''browning'''.<ref name="Bakker Clarke 2011 p. 23">{{cite book
| last1        = Bakker
| first1       = J.
| last2       = Clarke
| first2      = R.J.
| title       = Wine: Flavour Chemistry
| publisher   = Wiley
| year        = 2011
| isbn        = 978-1-4443-4600-8
| url         = https://books.google.com/books?id=4E8t6EGZwpMC&pg=PT23
| access-date = 18 September 2018
| page        = 23
}}</ref> In chemical terms, this is called a [[redox]] reaction because first the color of the wine deepens after fermentation through oxidation, and then the color begins to brown after bottling through reduction. Browning is not strictly considered a bad thing in every wine that is produced, as sometimes the oxidation process can contribute to the style of the wine in a positive and desirable way.
Generally speaking, however, browning is a sign of the wine going stale from too much exposure to oxygen.<ref>{{Cite news
| url   = http://winefolly.com/tutorial/how-to-tell-if-wine-has-gone-bad
| title = How to Tell if Wine Has Gone Bad {{!
}} Wine Folly|date=9 September 2015|work=Wine Folly|access-date=20 November 2017|archive-url=https://web.archive.org/web/20171201081918/http://winefolly.com/tutorial/how-to-tell-if-wine-has-gone-bad/|archive-date=1 December 2017|url-status=live}}</ref> Although [[Wine fault|wine that has gone bad]] is typically associated with the smell and taste of vinegar or unwanted [[effervescence]], oxidation itself can actually lead to "nutty", "applesauce", and "burnt marshmallow" aromas. The sharp vinegar component comes from [[Acetic acid bacteria|acetic acid]] formed through [[Acetic acid bacteria|bacterial processes]]. A lower [[pH]] level is typically preferred in wines because it decreases the overall risk of spoilage. The lower pH reduces the effect of browning and yields better colors, particularly in red wines.
== Significance of color ==
[[File:Bengt Frithiofsson evaluating wine.jpg|thumb|Swedish wine expert Bengt Frithiofsson tasting Chinese red wine]]
The color of a red wine will have many variables that influence it besides its exposure to oxygen that pertain to other [[Viticulture|viticultural]] aspects such as different growing climates, [[cultivar]]s, and production methods.<ref>{{Cite web
| url          = http://www.cornell.edu/video/genes-wine-color
| title        = Wine Color: It's All About the Genes – CornellCast
| website      = CornellCast
| access-date  = 20 November 2017
| archive-url  = https://web.archive.org/web/20171201043546/http://www.cornell.edu/video/genes-wine-color
| archive-date = 1 December 2017
| url-status     = live
}}</ref> For example, wines made from hybrid grapes can range anywhere from light pink to purple due to their chemical composition. Dr. Leo McCloskey, best known for his contributions in developing the [[Enologix]] software, points out that "Chemical ecology says that a wine's flavor, color and fragrance are expressions of its ecosystem."<ref>{{Cite news
| url          = https://www.nytimes.com/2005/08/07/magazine/the-chemistry-of-a-90-wine.html
| title        = The Chemistry of a 90+ Wine
| last         = Darlington
| first        = David
| date         = 7 August 2005
| work         = The New York Times
| access-date  = 20 November 2017
| issn         = 0362-4331
| archive-url  = https://web.archive.org/web/20171201134417/http://www.nytimes.com/2005/08/07/magazine/the-chemistry-of-a-90-wine.html
| archive-date = 1 December 2017
| url-status     = live
}}</ref>
However, when people perceive wines, the visual cues received from the color of the wine have a strong impact on their opinion of the wine. In a primitive sense, visual cues will generally have a stronger impact on humans than aromatic components since humans have evolved to identify things with eyesight, rather than through scent relative to other evolved species that rely on different sensory capacities more than they do on eyesight. This idea of a particular significance of color in the perception of wine is especially true in red wines.<ref>{{Cite web
| url          = http://www.cornell.edu/video/genes-wine-color
| title        = Wine Color: It's All About the Genes – CornellCast
| website      = CornellCast
| access-date  = 20 November 2017
| archive-url  = https://web.archive.org/web/20171201043546/http://www.cornell.edu/video/genes-wine-color
| archive-date = 1 December 2017
| url-status     = live
}}</ref>
Browning is therefore an important issue both for winemakers and for wine consumers, and is generally avoided. A well-known exception to this is [[sherry]], which is often purposely developed with oxidation as part of the production process; however, it can be considered a white wine since it is traditionally made from [[Palomino (grape)|Palomino]] grapes.
== Odor effects ==
[[File:Roasted-Marshmallow.jpg|thumb|189x189px|A scent often referenced in aged wines is that of a burnt marshmallow.]]
Through the aging of wine, its aroma compounds are affected as well. The [[ester]]s in the wine that were initially created during fermentation become reduced as they break back down into [[ethanol|alcohol]] and [[Carboxylic acid|carboxyl groups]] so the floral, fruity smells that are associated with freshness in a wine decrease. Meanwhile, the nutty, cooked smells increase through [[carbohydrate]] degradation.
== See also ==
* [[Wine fault]]
* [[Maderisation]]
== References ==
{{reflist}}
{{portalbar|Chemistry|Wine}}
[[Category:Wine]]
[[Category:Chemical reactions]]