A review of the current knowledge of red wine colour.

Nuno Mateus,Joana Oliveira,Ana Fernandes,Natércia Teixeira,Victor Armando Pereira De Freitas

doi:10.20870/oeno-one.2017.51.1.1604

Abstract

Anthocyanins are the main compounds present in young red wines, being responsible for their intense red colour. These pigments are mainly located in grape skins and their extractability during winemaking depends on many factors, such as their concentration in vacuoles and interaction with the cell-wall polysaccharides, affecting their stability and concentration in the must. The red colour of anthocyanins at wine pH is explained by the stabilization of the flavylium cation form that displays a red colour; otherwise at this pH the hemiketal colourless is the dominant form, bleaching the wine. Besides the contribution of free anthocyanins, a phenomenon called copigmentation influences the colour of young red wines. Copigmentation can be defined as a series of stabilization mechanisms involving van der Walls interactions that occur naturally in red wines and that can explain this unanticipated colour behaviour. Copigmentation is also pointed as the first interaction between anthocyanins and other wine components leading after that to the formation of new coloured compounds during red wine ageing. Some of these pigments have already been identified and characterized but many are still undiscovered. The detection and structural characterization of new pigments, and the knowledge of their chemical formation pathways are crucial to better understand the evolution of the colour of red wine during ageing.

Highlights

Colour is an important feature of red wine, being the first attribute to be perceived by wine consumers, and is directly associated with its quality
Red wines have a very complex matrix due to the wide variety of compounds extracted from grapes and to the metabolites released by yeast during the fermentation process
Acylated anthocyanins extracted from flowers, which present much more complex anthocyanin structures than grapes. display deep stable colours at neutral pH in the absence of any copigment, Goto and Kondo, 1991, Saito et al, 1972; Tatsuzawa et al, 2012). This can be explained by intramolecular copigmentation where the chromophoric part of the anthocyanin and the acyl residue exist in a folded conformation

Summary

Introduction

Colour is an important feature of red wine, being the first attribute to be perceived by wine consumers, and is directly associated with its quality. Among these molecules, aldehydes should have a higher impact on wines due to their increased reactivity towards flavonoids like flavan-3-ols and anthocyanins, Pissarra et al, 2003; Sousa et al, 2012). When the pH is raised to 3-4, the flavylium cation is involved in two parallel reactions in equilibrium: deprotonation to form the violet quinonoidal base and hydration at the C-2 position yielding the non-coloured hemiketal form. These forms are in equilibrium with the cis- and trans-chalcone forms which present a yellow colour, Pina, 1998). Malvidin-3-O-glucoside and its derivatives are usually the most abundant anthocyanins in young red wines, Mateus et al, 2001)

Interaction with cell-wall components

Intermolecular and intramolecular copigmentation

Self-association of anthocyanins

Findings

Conclusions