Although viticulturists refer to wine grape types as ‘varieties’, they are actually cultivars. For formal references to the cultivar, follow the general rule for cultivars (see Plant cultivars and breeding material), including using an initial capital:
Vitis vinifera ‘Shiraz’
Vitis vinifera ‘Cabernet Sauvignon’
However, a type of grape can be referred to by only the cultivar name:
Both Shiraz and Sauvignon grapes were used ...
Wines named after the predominant grape variety (cultivar) are called ‘varietals’. This applies to most Australian wine, and wine made in other ‘New World’ countries. Such wine names take initial capitals (eg Chardonnay, Merlot, Pinot Noir). Wines made in the ‘Old World’ (eg France, Spain) are named after the region they are from (eg Bordeaux).
