The only classical Old World wine region where co-fermentation is still widely practiced is now the
Côte-Rôtie appellation of northern
Rhône, while the use of white varieties in red Rioja and Tuscany wine has more or less disappeared. In Côte-Rôtie, the red variety
Syrah and the aromatic white variety
Viognier (up to 20% is allowed, but 5–10% is more common The reason why Viognier has been kept in Côte-Rôtie (while for example the white grapes
Marsanne and
Roussanne are hardly found any more in red
Hermitage or other red Rhône wines where they are allowed) is that it adds signature floral aromas to the wines. The popularity of Côte-Rôtie has led to
New World interpretations of this blend, most notably
Australian Shiraz-Viognier blends, which are also produced by co-fermentation. The reason why co-fermentation is not more widely practiced is that it "locks in" a certain blend already at the start of the fermentation, which gives the winemaker less possibility to adjust the blend after fermentation. Co-fermentation is also performed in situations where
field blend varietals are indistinguishable from each other, thus necessitating co-fermentation. ==References==