280 nm 45 min LC chromatogram of a red wine, showing mainly phenolic compounds.

Wine is a complex mixture of chemical compounds in a hydro-alcoholic solution with a pH around 4. The chemistry of wine and its resultant quality depend on achieving a balance between three aspects of the berries used to make the wine: their sugar content, acidity and the presence of secondary compounds. Vines store sugar in grapes through photosynthesis, and acids break down as grapes ripen. Secondary compounds are also stored in the course of the season. Anthocyanins give grapes a red color and protection against ultraviolet light. Tannins add bitterness and astringency which acts to defend vines against pests and grazing animals.[1]

Environmental factors such as soil, rainfall and fog affect flavor in ways that can be described collectively as "character" or the French term “terroir”.[1] As climate change disrupts long-established patterns of temperature and precipitation in wine-growing regions and causes more extreme weather events, the rate at which sugars, acids and secondary compounds develop during the growing season can be disrupted. Hotter temperatures and an earlier growing season can push chemistry of berries towards higher sugar content, less acids and differences in aromas.[1] Other factors such as smoke taint from fires[1] can negatively impact chemistry and flavor, resulting in flaws and wine faults that can make the wines undrinkable.

Types of natural molecules present in wine

Volatiles

Main article: Aroma of wine

Other molecules found in wine

Preservatives

Fining agents

Gum arabic has been used in the past as fining agent.[12]

List of additives permitted for use in the production of wine under European Union law:

Type or purpose of addition Permitted additives
Acidification tartaric acid
Clarification calcium alginate

potassium alginate
potassium caseinate
casein
isinglass
silicon dioxide
edible gelatine
acacia (gum arabic)
milk/lactalbumin
proteins of plant origin
ovalbumin (egg white)
alumino silicates
ferrous sulfate

Decolourants polyvinyl-polypyrrolidone (PVPP)

activated charcoal

Deacidification lactic bacteria

neutral potassium tartrate
potassium bicarbonate
calcium carbonate

Deodorant copper sulfate
Elaboration oak chips

metatartaric acid
water

Enrichment concentrated grape must

rectified concentrated grape must
saccharose
tannin
oxygen

Enzymes betaglucanase

pectolytics
urease

Fermentation fresh lees

ammonium bisulphite
thiamine hydrochloride
yeast cell walls
yeasts for wine production
diammonium phosphate
ammonium sulphate
ammonium sulphite

Sequestrants fresh lees

potassium ferrocyanide
calcium phytate
citric acid

Stabilisation calcium tartrate

potassium bitartrate
yeast mannoproteins
Preservatives sorbic acid
sulphur dioxide
argon
nitrogen
potassium bisulphite
dimethyl dicarbonate (DMDC)
carbon dioxide
potassium metabisulphite/disulfite
allyl isothiocyanate
lysozyme
potassium sorbate
ascorbic acid

Others

Wine faults

Main article: Wine fault

2,4,6-trichloroanisole, the chemical primarily responsible for cork taint in wines.

A wine fault or defect is an unpleasant characteristic of a wine often resulting from poor winemaking practices or storage conditions, and leading to wine spoilage. Many of the compounds that cause wine faults are already naturally present in wine but at insufficient concentrations to adversely affect it. However, when the concentration of these compounds greatly exceeds the sensory threshold, they replace or obscure the flavors and aromas that the wine should be expressing (or that the winemaker wants the wine to express). Ultimately the quality of the wine is reduced, making it less appealing and sometimes undrinkable.[14]

The yeast Brettanomyces produces an array of metabolites when growing in wine, some of which are volatile phenolic compounds. Brettanomyces converts p-coumaric acid to 4-vinylphenol via the enzyme cinnamate decarboxylase.[15] 4-Vinylphenol is further reduced to 4-ethylphenol by the enzyme vinyl phenol reductase. 4-Ethylphenol causes a wine fault at a concentration of greater than 140 µg/L. Other compounds produced by Brettanomyces that cause wine faults include 4-ethylguaiacol and isovaleric acid.

Coumaric acid is sometimes added to microbiological media, enabling the positive identification of Brettanomyces by smell.

Geraniol is a by-product of the metabolism of sorbate.

Fusel alcohols are a mixture of several alcohols (chiefly amyl alcohol) produced as a by-product of alcoholic fermentation.

See also

Notes

  1. ^ a b c d Chrobak, Ula; Zimmer, Katarina (22 June 2022). "Climate change is altering the chemistry of wine". Knowable Magazine. doi:10.1146/knowable-062222-1. Retrieved 11 July 2022.
  2. ^ a b c Villamor, Remedios R.; Ross, Carolyn F. (28 February 2013). "Wine Matrix Compounds Affect Perception of Wine Aromas". Annual Review of Food Science and Technology. 4 (1): 1–20. doi:10.1146/annurev-food-030212-182707. ISSN 1941-1413. PMID 23464569. Retrieved 11 July 2022.
  3. ^ Monoterpenes in grape juice and wines. M. Jiménez, Journal of Chromatography A, Volume 881, Issues 1–2, 9 June 2000, Pages 557–567, doi:10.1016/S0021-9673(99)01342-4
  4. ^ Terpenes in the aroma of grapes and wines: A review. J. Marais, S. Afr. J. Enol. Vitic., 1983, volume 4, number 2, pages 49-58 (article)
  5. ^ Inhibition of the decline of linalool and α-terpineol in muscat wines by glutathione and N-acetyl-cysteine. Papadopoulou D. and Roussis I. G., Italian journal of food science, 2001, vol. 13, no4, pages 413-419, INIST 13441184
  6. ^ Using LC-MSMS To Assess Glutathione Levels in South African White Grape Juices and Wines Made with Different Levels of Oxygen. Wessel Johannes Du Toit, Klemen Lisjak, Maria Stander and Dersiree Prevoo, J. Agric. Food Chem., 2007, Vol. 55, No. 8, doi:10.1021/jf062804p
  7. ^ Straightforward Method To Quantify GSH, GSSG, GRP, and Hydroxycinnamic Acids in Wines by UPLC-MRM-MS. Anna Vallverdú-Queralt, Arnaud Verbaere, Emmanuelle Meudec, Veronique Cheynier and Nicolas Sommerer, J. Agric. Food Chem. 2015, 63, 142−149, doi:10.1021/jf504383g
  8. ^ Günata, Ziya; Wirth, Jérémie L.; Guo, Wenfei; Baumes, Raymond L. (2001). "C13-Norisoprenoid Aglycon Composition of Leaves and Grape Berries from Muscat of Alexandria and Shiraz Cultivars". In Winterhalter, Peter; Rouseff, Russell L. (eds.). Carotenoid-Derived Aroma Compounds. ACS Symposium Series. Vol. 802. p. 255. doi:10.1021/bk-2002-0802.ch018. ISBN 0-8412-3729-8.
  9. ^ P. Winterhalter, M. A. Sefton and P. J. Williams (1990). "Volatile C13-Norisoprenoid Compounds in Riesling Wine Are Generated From Multiple Precursors". Am. J. Enol. Vitic. 41 (4): 277–283. doi:10.5344/ajev.1990.41.4.277. S2CID 101007887.
  10. ^ Zelena, Kateryna; Hardebusch, Björn; Hülsdau, BäRbel; Berger, Ralf G.; Zorn, Holger (2009). "Generation of Norisoprenoid Flavors from Carotenoids by Fungal Peroxidases". Journal of Agricultural and Food Chemistry. 57 (21): 9951–5. doi:10.1021/jf901438m. PMID 19817422.
  11. ^ Cabaroglu, Turgut; Selli, Serkan; Canbas, Ahmet; Lepoutre, Jean-Paul; Günata, Ziya (2003). "Wine flavor enhancement through the use of exogenous fungal glycosidases". Enzyme and Microbial Technology. 33 (5): 581. doi:10.1016/S0141-0229(03)00179-0.
  12. ^ Vivas N, Vivas de Gaulejac N, Nonier M.F and Nedjma M (2001). "Incidence de la gomme arabique sur l'astringence des vins et leurs stabilites colloidales" [Effect of gum arabic on wine astringency and colloidal stability]. Progres Agricole et Viticole (in French). 118 (8): 175–176.((cite journal)): CS1 maint: multiple names: authors list (link)
  13. ^ Lamont, Kim T.; Somers, Sarin; Lacerda, Lydia; Opie, Lionel H.; Lecour, Sandrine (2011). "Is red wine a SAFE sip away from cardioprotection? Mechanisms involved in resveratrol- and melatonin-induced cardioprotection". Journal of Pineal Research. 50 (4): 374–80. doi:10.1111/j.1600-079X.2010.00853.x. PMID 21342247. S2CID 8034935.
  14. ^ M. Baldy "The University Wine Course" Third Edition pgs 37-39, 69-80, 134-140 The Wine Appreciation Guild 2009 ISBN 0-932664-69-5
  15. ^ Brettanomyces Monitoring by Analysis of 4-ethylphenol and 4-ethylguaiacol Archived 2008-02-19 at the Wayback Machine at etslabs.com

References