Samiksha Jaiswal (Editor)

Wine chemistry

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Wine chemistry

Wine is a complex mixture of chemical compounds in a hydro-alcoholic solution with a pH around 4.

Contents

Types of natural molecules present in wine

  • Acids in wine
  • Phenolic compounds in wine
  • Proteins in wine
  • Sugars in wine
  • Yeast assimilable nitrogen
  • Minerals
  • Dissolved gas (CO2)
  • Monoterpenes and sesquiterpenes such as linalool and α-terpineol
  • Glutathione (reduced and oxidized)

    • Volatiles

  • Methoxypyrazines
  • Esters : Ethyl acetate is the most common ester in wine, being the product of the most common volatile organic acid — acetic acid, and the ethyl alcohol generated during the fermentation.
  • Norisoprenoids, such as C13-norisoprenoids found in grape (Vitis vinifera) or wine, can be produced by fungal peroxidases or glycosidases.

    • Conservatives

  • Ascorbic acid is used during wine making
  • Sulfur dioxide (SO2), a preservative often added to wine

    • Fining agents

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

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

    Others

  • Melatonin
  • Wine lactone
  • Anthocyanone A, a degradation product of malvidin under acidic conditions

    • Wine faults

    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.

    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. 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 and, thus, is a very unpleasant contaminant of wine if bacteria are allowed to grow in wine.

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

    References

    Wine chemistry Wikipedia
    (Text) CC BY-SA