By Philip Fine   A grape with French origins, but long used in California winemaking, has been added to the list of prime grape varieties accepted for use in marketing geographically designated American wines. Tannat, which produces a deeply coloured and tannic wine, has been given official US wine-making status by Washington's Bureau of Alcohol, Tobacco and Firearms after a petition was launched by Tablas Creek Vineyard in Paso Robles, California.