The production of the wine of Cos d’Estournel is labor intensive starting the moment the grapes enter the gleaming new facility. The berries travel through a tunnel that instantly lowers the temperature of the fruit to 3-5 degrees Celsius. This sudden chilling stops the loss of juice while also slowing oxidation. Next, the grapes are cold macerated at 7-9 degrees Celsius for about a week. Pump overs are done by gravity recycling. The juice from the top of the vat moves to the bottom of the vat entirely by gravity. The fermentation takes place at low temperatures to avoid over extraction or harsh tannins.
Jean-Guillaume Prats in a discussion on 2009 Cos d’Estournel explained the role of the new cellars in producing the wine, “Gravity cellars allow for a complete non intervention in making the wine. The use of gravity allows for the purest possible expression of the fruit grown in the gravelly rock terroir of Cos d’Estournel. Today, the wine is always moved by gravity. It’s never forced or touched by human hands.”
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With thanks to Jeff Leve from http://www.thewinecellarinsider.com, for the invaluable information