~ Robert Craig
Wine grapes can be grown in a wide variety of soils and climates. In fact, every state in the USA, from Alaska to Arizona, has some production of wine. However, moving up the ladder in terms of potential wine quality, the range of suitable conditions narrows dramatically. At the top of this scale, the combination of soils and micro-climates needed for maximum quality wine is quite specific.
This brings us to a concept known as “terroir”. There is no universal agreement as to what this elegant term encompasses as it relates to wine quality. Some argue that “terroir” involves the full range of natural conditions and the human input of decision-making in grape growing and winemaking.
Personally, I prefer the more restrictive definition of terroir, which is the inherent natural attributes of a location that provide a contextually limiting framework for what can be achieved in grape quality. A good application of this definition is found right here in California.
The Central and Sacramento Valleys are where most of the grapes in the state are grown. Generally deep and fertile soils and very warm temperatures characterize these two locations. These are ideal conditions for producing grapes in great quantity, but not suited for grapes of great quality. Vineyards here can produce 10 to 15 tons per acre of modest quality fruit.
In the Napa Valley and other Coastal areas, the terroir is greatly different, which is reflected in both the quality and quantity of grapes produced. The combination of less fertile soils and more moderate summer temperatures yields grape crops of lower production but significantly better quality.
Fog regularly rolls into Napa Valley during the summer from
nearby San Francisco Bay, contributing to cooler temperatures
and varied micro-climates.
One of the signature attributes of Napa Valley is its Mediterranean climate, with moderately warm, dry and sunny days and cooler evenings during the summer months. This weather pattern allows the grapes to fully mature over a long growing season, without the metabolization (loss) of the acids that occurs in hotter climates. Also, soils in Napa Valley are less fertile and more well-drained than further inland. This results in smaller grapes with more intense flavors. Crop yields in Napa Valley generally range from 2.5 to 5 tons per acre.
The interplay of soils and microclimates is another hallmark of Napa Valley. In this regard, Napa is an extraordinarily diverse location. The Valley is only about 30 miles long and ranges between 10 and 15 miles wide. Within this relatively small land area, there are 46 different soil types (which is more than in all of France). In addition, as the natural topography influences the movement of cooler air from the San Francisco Bay northward up the Valley, numerous pockets of this cooler air, or micro-climates, are formed.
This natural combining of geology, topography, soils and climate also influences the character of the wines. The specific combination of these factors imprints recognizable aromatic and fruit characteristics on grapes grown in specific locations.
This has been acknowledged in the designation of American Viticultural Areas (AVA’s) within the Napa Valley. The AVA system gives recognition to the overall high quality and unique sensory profiles of wines produced from grapes grown within defined boundaries.
That said, the role of man cannot be overlooked in the ultimate realization of maximum wine quality from a specific location. Myriad decisions of vine spacing, rootstock, varietal (clone), trellis design, pruning method, ripeness determination, picking date, fermentation regime, choice of yeast, barrel selection, aging and blending decisions and numerous other factors are key determinants of wine quality.
These decisions will greatly influence how well the winemaker achieves ultimate wine quality and the style that he or she seeks within the constraints of the vineyard's terroir.
In subsequent writings I will explore how the concept of terroir fits into our own wine program at Robert Craig Winery and the wines we produce from various AVA’s in the Napa Valley.
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