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Napa Valley AVA

by David on June 25, 2009

Napa Valley is a strange and wonderful place, perhaps in equal parts. In an area about 1/8 of the size of Bordeaux, we are able to grow a great number of different grape varieties with remarkable success. For the wonderful array of Napa Valley wines we enjoy today, we owe our thanks to Mother Nature and some rather impressive mood swings on her part.
It appears we have a history of violence, geologically speaking. Over the last 10 million years, massive collisions of the earth’s crust created our mountains and valleys. Repeated volcanic eruptions spewed forth rock, lava and ash, and created some of the small knolls you see as you drive through the valley. Changing sea levels sent flood waters washing in and out of the valley like the waves of the sea, depositing layers and layers of sedimentary clay and sand of vastly different ages. These major events, in conjunction with many minor ones, worked together to create an area of unsurpassed beauty and diversity.

What it all adds up to, is that 33 different soil profiles, representing half of the soil orders that exist on the planet can be readily found in the Napa Valley1. It’s important to note that all of this exists in an area that produces about 4% of California’s wine2. Extensive soil diversity can also be found within individual sub-appellations, such as the Spring Mountain District, an area that encompasses only 8,600 acres and contains 22 different soils series. What this means, is that viticulturists shouldn’t assume that a vineyard site, even a small one, will be uniform in soil type. Our own 9.5 acre vineyard at Goosecross is divided into 10 different sections according to variety, clone3 of the variety, rootstock hybrid4 and vine spacing – the last two factors mainly due to variations in the soil.

Today, the most striking geographic features are the two mountain ranges, the Mayacamas to the west, and the Vaca range on the east side, which form our valley. It’s about 30 miles long and a few miles wide, narrowing as it goes north, and bi-sected by the Napa River. First time visitors to the valley are surprised to notice a marked difference in appearance between the Mayacamas and the Vaca ranges. The Mayacamas is heavily forested and perpetually green. The Vaca range is dry in the summer, a home for sagebrush and scrub oaks, due to lighter rainfall, generally shallower soils and from baking in the afternoon sun.

The San Pablo Bay at the southern end of the valley, together with the mountain ranges, holds the key to our agreeable climate. Wine grapes are at their best when they ripen relatively slowly, and the bay serves as our natural air conditioner. In the summertime, as the daytime temperatures increase, the warm air rises and pulls in cooling evening fog from the bay. The mountains help to funnel in the fog and wind and moderate our temperatures. Here in Yountville, we often see a daytime high of 85° F and a drop to 55° at night during the growing season.

Since the bay is located at the southern end of the valley, marine influences are greatest in the south and diminish as the valley meanders north. Vive la difference! It allows us to grow a number of different grape varieties very, very well. Burgundian and Champagne varieties, such as Chardonnay and Pinot Noir, ripen slowly in the foggy, breezy southern end of the valley. Varieties that need more heat to ripen are planted in the upper regions. Of course, Cabernet is King in the Napa Valley, and it’s because of the marvelous results we’ve enjoyed decade after decade. It can be found all over the valley, but it’s concentrated in the mid-valley area. Because of our geographic variability, you can find warm and cool pockets virtually anywhere, so we’re speaking in general terms. We can never make assumptions about what to grow before planting a new vineyard. We must measure the meso-climate5 and collect soil samples in order to make a good decision.

With such diversity of soil and climate, we know that different vineyard locations can produce wines that vary in character and style, but also have a track record of making wines that are reliably high in quality.

It comes as no surprise that Napa Valley was the first American Viticultural Area (What is an AVA?) in California, approved in 1981. The first vineyard in the Napa Valley was planted in 1836, by George Yount, in what is now known as the Yountville District. In 1861, Charles Krug established the first commercial winery in the Napa Valley. In the late 1800s, H.W. Crabb catalyzed a spirit of innovation that still thrives today, by planting more than 400 grape varieties as a research project on his Oakville estate. By 1889, the Napa Valley was home to more than 140 wineries.

In the early days of winemaking in the Napa Valley, the most popular varieties were planted all over the valley without much attention paid to environmental circumstances. We just didn’t know any better at the time. As we’ve gained a greater understanding of the valley’s climates and soils (an on-going process!), we’ve realized the wisdom of matching the right variety with the right place. Consequently, we have divided it into sub-appellations according to those differences. This was a natural evolution, as we came to know the valley better. So, we have the entire Napa Valley as an AVA, and smaller districts within it too.

Since it’s grown all over the valley, Cabernet Sauvignon is a great model of our diversity. It can be a great discovery and delight to taste and compare Cabs from different parts of the valley. Are you in the mood for a muscular Howell Mountain Cab or an elegant Yountville District Cab? You can savor and enjoy each in its own way, and realize as you do, that it’s all thanks to Mother Nature and her ever-changing moods!

Footnotes:
1. Napa Valley Vintner’s 2004 Soil Report press release
2. California Wine institute website
3. Clone: A clone is a sub-variety within a grape variety (a natural mutation), such as Chardonnay, that has been replicated because of specific attributes such as flavor, productivity and adaptability to growing conditions.
4. Rootstock: Wine grapes cannot be grown on their own roots in most parts of the world, due to lack of resistance to certain soil pests. They are grafted onto various rootstock hybrids that are resistant to the pests. Additionally, the hybrids are chosen for other beneficial traits, such as low or high vigor, drought resistance, etc.
5. Mesoclimate: The climate of a vineyard site, hillside or valley. The term “microclimate” is used in its place extremely often. Microclimate correctly refers to the climate immediately surrounding the individual vine canopy (or green growth) and clusters. Vineyard and canopy management will strongly influence the microclimate, but not the mesoclimate.

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