Nonflavanoids and Color in White Wine
Nonflavanoids are the primary contributor to the color white wine. Compared to color in red wine, the chemical nature of color in white wine is not very well understood. The majority of the phenols in white wine are nonflavanoid hydroxycinamates. These include caftaric acid, coumaric acid and ferulic acid.
Some believe that the color characteristic yellow color of young white wine arises from the oxidation of flavanols like quercetin and kaempferol. In addition to this, nonflavanoids from oak cooperage contribute to the color.
The deep yellow color of white wines that have been aged most likely comes from the oxidation of phenols or galacturonic acid. The oxidation of phenols has been shown to shift its absorbtion spectrum to the visible range.
Generally, nonflavanoids are more structurally simplistic than flavanoids. In wines that are not aged in oak, nonflavanoids are primarily derivatives of hydroxybenzoic acids and hydroxycinamic acids.
The most common form of nonflavanoids are hydroxycinamic acid derivatives. They are commonly esterified to organic acids, sugars, alcohols, and most commonly tartaric acid.
Examples of these derivatives are caftaric, fertaric and coutaric acids – these are the combination of tartaric acid with the hydroxycinamic acids; caffeic, ferulic and courmaic acids, repectively.
Caftaric acid plays an important role in phenol oxidation and oxidative browning in must.
The oxidized derivatives of coutaric and caftaric acid provides the yellowish-gold color in white wine.
Wines that are aged in oak contain elevated levels of hydroxylbenzoic acid derivatives. The most notable of these is ellagic acid, which is comprised of two molecules of gallic acid. Esters of ellagic acids enhance the color of red wine by acting as copigments with anthocyanins.
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