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When wine has a thirst for research. © FOTOLIA, Fotolia

When wine has a thirst for research

Wines of every hue

From white to red, and passing through very pale pink or cherry red, the palette of wine colours is immense.  White grapes only produce white wines which have fruity, fresh and light characteristics.  As for black grapes, they can be used to make red, rosé or even - in some cases - white wines (Pinot noir and Pinot Meunier in Champagne). It is anthocyanins which give them their red colour.

Updated on 11/15/2013
Published on 11/15/2013

La vie en rosé

Rosé wines are not made by mixing white and red wines.  This practice is only authorised in some particular cases, such as pink champagne.  The principal distinction is between rosé made by direct pressing (whole or stripped bunches of grapes are pressed directly) or using the saignée (bleeding) technique (where the grapes are placed in vats in the same way as when producing a red wine, but only macerated for a very short period of time).  To define and appreciate the quality of a rosé wine, the first criterion for consumers is colour.  A major study conducted by INRA, the Centre du Rosé and the French Wine Institute enabled the screening of a collection of 298 rosé wines from 21 countries throughout the world, and it revealed the molecules and mechanisms responsible for their very broad palette of colours.

What about yellow wines?

Produced exclusively in the Jura region of France, vins jaunes (yellow wines)  are raised in a particular way.  During their ageing - for between three and six years - the wine develops its colour and a typical nose reminiscent of walnut, curry or hazelnut.  This is due to the presence of a compound that has been chemically identified and is called sotolon.  In the kitchen, this small molecule can be added (in very small quantities) to a brioche dough to enhance its flavour.

How does a wine change its colour?

Sight is the first sense that is elicited during a tasting.  The robe (colour) of a wine constitutes its external aspect, and several factors can influence this colour.  Such differences, and notably the differentiation between white and red grapes, are above all linked to genetics: work carried out by INRA has revealed the molecular mechanisms (regulatory genes) involved in genetic variations in the content of anthocyanins.  But the synthesis of pigments is also dependent on ripeness, climatic conditions and, first and foremost, on the intensity of solar radiation.  A lack of sunshine produces red grapes that are only lightly coloured, which is why northern regions mainly cultivate white grape varieties.  Two other parameters define whether a red, white or rosé wine will be obtained: the timing of pressing1 and the duration of maceration2.  The later the pressing, the more strongly will the juice be coloured.  For white wines, pressing is generally immediate and there is no maceration, while for red wines, pressing is performed at the end of maceration. In addition, the colour of a wine can provide some clues as to its age.  Indeed, red wines lose their colour as they age, changing from a dark purple to a tile-red.  As for white wines, they can develop from pale to golden yellow, or in some cases may take on a brownish coloration.

1 After destemming and crushing, the winemaker collects the free run wine.  The marc (solid components) remain in the vat and are then pressed to obtain the press wine, which has a stronger colour and contains more tannin (pressurage).  The free run wine and press wine can then be assembled immediately or after ageing, or be aged separately.
2 Maceration: phase during winemaking when the solid parts of the berries - the skins - macerate in the juice.

Ice wines

These wines are produced using grapes that have frozen on the vine.  Harvesting only starts once the temperature has reached at least -7°C.

Gamay Fréaux

Gamay Fréaux. © INRA, Zhanwu Dai & Wenling Xia
Gamay Fréaux © INRA, Zhanwu Dai & Wenling Xia