The key variable (French protestations of terroir notwithstanding) is climate. Consider Cabernet Sauvignon. I do not believe the soils of the Médoc are all that different from the soils of the central Napa Valley. Although they may differ in their chemical components, both are well-drained. (It is difficult to craft generalizations about Napa Valley soil since there are at least 33 different types that have been identified so far, courtesy of the jumbling effects of plate tectonics). The best vineyard sites all show this incapacity to hold water, which makes them sparse in nutrients.
The fundamental difference between central Napa Valley and the Médoc, therefore, is climate. The Médoc lies at roughly 44 degrees north latitude, while Napa Valley is 38 degrees north latitude. This places Napa Valley on approximately the same latitude as Spain, making it closer to the equator. Bordeaux lies in a Continental climate zone, whereas Napa Valley’s climate is Mediterranean.
The mean high temperature in Bordeaux in July-August is about 80 degrees F (27 degrees C); in Napa Valley (St. Helena) by contrast it is close to 90 degrees F (32 degrees C). And, of course, Napa’s late summer heat waves are notorious. This difference has a vast effect on grape ripeness. The 2009 Chateau Margaux, for example, is 13.3% alcohol. There are few Napa Valley Cabernets with alcohol levels that modest. Many these days approach 15%, if in fact they do not exceed it. The Paul Hobbs 2007 Stagecoach Vineyard Cabernet Sauvignon–a spectacular wine–has 15.1% alcohol,. True, Napa Valley grows Cabernet Sauvignons with lower alcohols, such as the lovely Corison 2007, which has 13.8%; but these are in the minority. What happens to a Cabernet when the alcohol is high (the result of grapes picked at higher sugar levels)? They are richer and more full-bodied. Softer, too, since acidity drops with ripeness. These wines will be marked by an abundance of fruit–in the case of Napa Valley Cabernet, generally blackberries and cassis, perhaps even chocolate, although a cooler vintage may yield cherries. This is a very different profile from a Bordeaux classified growth, which will exhibit earthier notes, higher acids and harder tannins. Why Napa Valley should be California’s (and probably the New World’s) greatest home for Cabernet Sauvignon is explicable in two ways. The valley lies one mountain range (the Mayacamas) further inland than Napa’s nearest quality competitor, Sonoma County, and is therefore that much warmer; and the Cabernet needs warmth to ripen.
Then, too, Napa has a long history of growing Cabernet, at least 150 years; it is a place where wealthy men always could lavish their money on the quality of their wines. (This is certainly truer today than ever.) Visionaries such as Georges de Latour, at Beaulieu, and Charles Krug set the pace; intermediaries, including the great André Tchelistcheff, pushed the boundaries; and, with the explosion of the “boutique” winery movement, in the 1960s and 1970s, Napa Valley pursued Cabernet Sauvignon with the ardor of a knight-errant seeking the Holy Grail. Today, we see a Napa Valley in which vineyards have crept up into the two mountain ranges that define it (Mayacamas on the west, Vaca Mountains on the east). Entire new areas of highland viticulture are being excitingly discovered and developed. It is entirely likely that, from Atlas Peak (an official appellation) and Pritchard Hill (not yet declared, but probable in the future), the greater Napa Valley region will produce Cabernet Sauvignons and Bordeaux blends the likes of which we have not seen before (and Syrah, interestingly and increasingly, is being added to the blend, for depth and greater complexity).
Written by Steve Heimoff