WINETECH Technical Yearbook 2021

OENOLOGY RESEARCH | NOVEMBER 2021

REMI SCHNEIDER 1 , MICHEL MOUTOUNET 2 & ELDA BINNEMAN 3 : 1 Oenobrands; 2 Private consultant; 3 Anchor Oenology KEYWORDS: Grape phenolic compounds, wine colour, taste. A story of taste, colour and phenolics

PHENOLIC COMPOUNDS are abundant in the plant kingdom. They are derived from phenol, which is the basic structure of all phenolic constituents and when containing one or more phenolic rings, they are generally referred to as polyphenols. These phenolic compounds play an essential role in the grapevine’s defence mechanisms against biotic and abiotic stressors. They are also strongly linked to wine quality, colour and flavour. The main grape polyphenols of oenological importance are the non-flavonoids, including the group of phenolic acids, and within the flavonoids group, the anthocyanins and tannins are the major role-players. It is important to understand the reactivity of phenolic compounds and GRAPE PHENOLIC COMPOUNDS

the interaction phenomena that explain the mechanisms for change during the fermentation and post-fermentation stages. These mechanisms include condensation reactions, co-pigmentation and various tannin interactions. Below we look at the main phenolic reactions taking place during fermentation. THE FATE OF PHENOLIC COMPOUNDS DURING THE FERMENTATION PHASE A. Production of phenolic acids The tartaric esters of hydroxycinnamic acids (caftaric, coutaric and fertaric acid) in grapes, which have not taken part in must oxidation phenomena, see a 30% drop in concentration during fermentation. They undergo changes due to the metabolic activity of microorganisms (yeast and bacteria).

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