Trace metals alter wine colour, scientists find

A team of Spanish scientists has discovered how trace metals in grapes and fermenting wine affects the colour of the final product.

Using Tempranillo samples grown by the vinicultural department at the University of Navarra in northern Spain, researchers have discovered that minute changes in the amount of iron, zinc, copper and manganese present dramatically alters the colour of wine.

The research, which was carried out over three successive harvests, shows that small extra amounts of iron in wines can produce an increase of between 8% and 30% of its blue component with a proportionate decrease in its percentage of red.

The scientists concluded that hues – varying from bluish red to an earthy orange – are also affected by the stability and reactivity of the metals the wine contains.

They also found that most iron is concentrated in the skin of the seed, and that the amount of iron and copper present drops considerably in the first days of fermentation.

The team worked out a mathematical formula to allow growers and producers to quantify and predict colour and shading precisely. This could be used as an objective index of quality.

Future studies, including one to precisely measure the impact of aluminium on wine hue colour, are also being planned.

Written by Emmet Cole