The world of white Bordeaux is largely defined by the area's varied sub-regions. The soils and climate, not to mention the economics and history of each appellation, provide a window on the differences between, for example, white wines from Pessac-Léognan and Entre-Deux-Mers. But as much as these factors affect the flavors of the white Bordeaux in your glass, the grape varieties that are grown and blended to make these prized wines are of equal importance.
 
Many wine enthusiasts are aware that Sémillon and Sauvignon Blanc form the foundation of the white wines of Bordeaux. But other grapes, some well-known and others more obscure, often find themselves in the final blends of many estates. And it is the ability of the region’s winemakers to blend these different grape varieties that distinguish Bordeaux from other regions like the Loire Valley or Marlborough in New Zealand whose wines are made solely from Sauvignon Blanc.
 
Here’s a brief overview of the grapes and their contribution to Bordeaux Blancs.
 
Sauvignon Blanc: The region's most well-known grape variety despite making up less than 40% of the white grapes planted in Bordeaux. Most wines from the white only Entre-Deux-Mers appellation are made entirely with Sauvignon Blanc though there is a smattering of Sémillon in some blends. They are also made with very little oak influence. In the more famous Pessac-Léognan, this fresh and lively varietal usually plays a lesser role to the richer textured Sémillon grape.
 
Sémillon: This is the most popular white wine grape planted in Bordeaux accounting for over half of the vineyards devoted to white wines. Sémillon contributes body and texture to a white Bordeaux blend and it is most frequently used in Graves and Pessac-Léognan. There is no formal regulation or rule of thumb as to how much Sémillon is part of the final blend of a grand vin with some Pessac wines as high as 84% in 2012 and others as low as 5% the same year.
 
Muscadelle: Despite its similar nomenclature, this grape is not related to the popular Muscat grape. About 7% of Bordeaux's white grapes are dedicated to this grape variety which is prized among many producers for its delicate aromatic contributions. Difficult to grow because of its susceptibility to disease, it has fallen from favor over the years and is seen less frequently. Nevertheless, a little Muscadelle can add a dimension of complexity so do not expect this unique variety to disappear soon.
 
Sauvignon Gris: This grape variety is beginning to make a more assertive appearance among some of the white wines made by Saint-Emilion wineries (though note that white wines made here will not carry the Saint-Emilion AOC). Sauvignon Gris is a clonal mutation of Sauvignon Blanc and comprises 2% of all the white grapes grown in Bordeaux. It is appreciated for its ability to ripen early with full-bodied textures. About one-third of the white wines from Jean-Luc Thunevin’s Château Valandraud and Gérard Perse’s Château Monbousquet are composed of Sauvignon Gris, a very high proportion from some of the most forward thinking winemakers of the Right Bank.
 
Colombard: A grape that is widely used in the production of Cognac, it also has an historic home on the Right Bank of the Gironde River in the communes of Blaye and Bourgeais. It is appreciated for its aromatic contribution to the final blend. It can play the leading role in many white wines from the Côtes-de-Blaye with smaller proportions of the other Bordeaux white varieties acting in support.
 
Ugni Blanc: Like Colombard, Ugni Blanc is also confined to the areas of Blaye and Bourgeais located across the Gironde River from Pauillac. Also known as Trebbiano, this grape is found primarily in nearby Gascony and is more commonly a component of brandy production where locals interestingly refer to it as “Saint-Emilion”. The grape is very resistant to disease and appreciated for its acidity which may account for its continued presence near the river.