Metals involved in the colour of wine

A University of Navarre research team, made up of Irene Esparza, José María Fernández, Carolina Santamaría, María Isabel Calvo and José Mª García-Mina, have studied the influence of a number of metals in giving wine its colour. The work concluded that a slight change in these elements substantially modifies certain aspects of the quality of the ferments.

Scientists know that colour is one of the main parameters that enable the excellence of the product to be measured, providing as it does information about structure, body and taste. In fact, it is known that the hues, varying from bluish red to an earthy orange, are influenced by -amongst other factors – the stability and reactivity of metals present, such as iron, zinc, copper and manganese.

To carry out the study, they took samples of the Tempranillo variety of grape from a plot supervised by Evena (the Navarre Viniculture and Enological Station), located in Erriberri (Olite) in Navarre. The sample musts and wines were taken from three successive harvests starting in 2002 and which were subject to identical fermentation treatments, the only differentiating factor being meteorological conditions.

Using this method, the preferred location for the metal components in the grape seeds was identified and also how their proportion is modified during the fermentation process. The results show that most iron concentrates in the skin of the seed and that the amount of this metal, together with that of copper, drops considerably in the first days of fermentation.

Shades of colour a la carte

Moreover, the researchers derived a mathematical expression that enables the quantification of these colour changes in a precise way, thanks to which “the wine-producer can measure the shade of colour with great precision and thereby have objective indexes of quality”. This will be published shortly in the specialised magazine, Analytica Chimica Acta.

They also concluded that a small quantity of iron in wines produces an increase of between 8% and 30% of its blue component, with a consequent similar decrease in its percentage of red. Finally, in subsequent studies results will be presented as a function of varying the quantity of other metals, such as aluminium or copper, in order to determine the effect on changes in colour.