Wine chemistry
is a complex mixture of chemical compounds in a hydro-alcoholic solution with a pH around 4.
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
- Monoterpenes and sesquiterpenes such as linalool and α-terpineol
- Glutathione
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 or wine, can be produced by fungal peroxidases or glycosidases.
Other molecules found in wine
Preservatives
- Ascorbic acid is used during wine making
- Sulfur dioxide, a preservative often added to wine
Fining agents
List of additives permitted for use in the production of wine under EU 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 milk/lactalbumin proteins of plant origin ovalbumin alumino silicates ferrous sulfate |
| Decolourants | polyvinyl-polypyrrolidone 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 carbon dioxide potassium metabisulphite/disulfite allyl isothiocyanate lysozyme potassium sorbate ascorbic acid |
Others
- Melatonin
- Wine lactone
- Anthocyanone A, a degradation product of malvidin under acidic conditions
Wine faults
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.
Fusel alcohols are a mixture of several alcohols produced as a by-product of alcoholic fermentation.