Michaël Jourdes

Senior Lecturer at the University of Bordeaux and researcher at the ISVV within the oenology research unit

Published in "Terre de vins" No. 81 – January 2023

What gives wine its colour?

The colour of grapes and wines is linked to anthocyanins, molecules responsible in the plant kingdom for numerous colour variations in flowers, leaves and berries. Found predominantly in the skins of the world’s main grape varieties, and more rarely in the pulp of others, anthocyanins are extracted during winemaking. The evolution of a wine’s colour as it ages is then influenced by two key factors: acidity and oxygen. As wine is an acidic and oxygenated environment, the highly reactive anthocyanins interact with other phenolic compounds, including tannins, to stabilise the colour.

The colour of wine comes mainly from anthocyanins, the development of which depends on acidity and oxygen. It provides information about the wine’s age and grape variety, whilst research is being carried out into how it changes in response to global warming and new winemaking practices.

What does the colour of wine tell us?

It can provide clues as to the wine’s age. When young, it will tend to be red with violet highlights; then, as it ages in the bottle, the pigments resulting from the interaction between anthocyanins and tannins oxidise, and it will take on orange, brick-red or terracotta hues. The colour can also provide clues as to the grape variety; a Syrah, for example, will be much richer in anthocyanins than a Pinot Noir, and may even influence certain aromatic descriptors. A study showed that when a white wine was tasted, and then the same wine was artificially coloured, the tasters’ descriptions of it changed. This is because our brains are more accustomed to believing what they see than what they can smell. Consequently, for rosés, colour is one of the primary criteria influencing the decision to buy, with demand for increasingly lighter-coloured wines having grown over the past twenty years or so.

What areas does your research explore in relation to this topic?

We are working on two areas relating to colour development. The first concerns changes in pH levels due to global warming, as the acidity at the time of harvest affects the colour of the wine. The second aims to understand the mechanisms behind colour development in relation to acidity and oxygen levels. We are studying new compounds and their formation, and are examining
the role of oxygen in relation to different ageing methods – whether in barrels or not – and different types of closures. We are also investigating the impact of sulphur-free winemaking on colour. Among emerging topics, the arrival of new, so-called ‘resistant’ grape varieties has prompted studies into their anthocyanin composition – which differs from that of traditional varieties – and their capacity to evolve during ageing.