A shorter version of this article first appeared in Wine and Spirit in 2007, since merged into Harpers Wine and Spirit.
Co-fermentation seems to be a recent buzz word from the new world, but truth be known, the French have been using this technique almost forever.
It is the simultaneous fermentation of two or more grape varieties in the same vat. The ‘field blends’ of California fame spring to mind, as do the accidental co-fermentation of Chilean merlot-merlot with carmenere, before they sorted out that they were dealing with two different grape varieties.
Viognier gives floral aromas. Syrah gives raspberries and strawberries.
Most commonly though, syrah/shiraz and viognier are the players/protagonists and the scene is Côte Rôtie, in France’s Rhône valley, where up to 20% of viognier is permitted in the blend, where viognier is mixed with syrah in the vineyard, and shiraz-rich bits of the new world.
Pierre Gaillard, of the eponymous French domaine said, for his Côte Rôtie: “we pick the grapes together, we macerate and ferment both grapes together. Viognier has more sugar than syrah, so helps to raise alcohol in the wine. This means more fatness, more structure, a softer structure, more flavours in the wine. Because viognier is a very aromatic variety, the skins give the wine floral aromas, such as violets. The syrah gives more cassis, raspberries and strawberries.” He said the floral aromas help with freshness in the wine, which is one of the typical traits of Côte Rôtie – “it can be a full bodied wine, but it always stays quite fresh, and the viognier helps for more complexity and elegance.”
Gaillard uses viognier berries, which are all destemmed, with the syrah before going to the vat. But there are other techniques, such as using just the skins of viogner. Erlank Erasmus, winemaker of the South Africa’s Goats do Roam range, said of the Goat Roti, a co-fermented syrah/4% viognier, “viognier skins are put into shiraz ferment. They help stabilise colour, making the wine darker, and elevate the fruit of the wine, giving freshness and a floral character, and softening the palate structure.”
Viognier flowers and textural modification are key attractions of the technique. Warren Gibson, winemaker at New Zealand’s Trinity Hill said: “the tannin molecules in viognier stabilise red pigment, but we do it for the lovely aromatics – floral, blossom, dried apricots, ginger. It also gives a creamy mid palate, a textural feel not seen with varietal syrah.”
So simply blending a bit of viognier into a syrah/shiraz would not have these floral, structural and visual effects, and would probably dilute and simplify the wine instead. The scientific understanding of the processes involved is still at an early stage. Whether it suits other grape varieties, with synchronous ripening times, is open to experimentation.