The Impact of Terroir in Chiles Valley Wine Country

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The terroir of Chiles Valley Wine Country has a number of unique features that make it suitable for fine wine production.

The AVA is located in the Vaca Hills to the east of the Napa Valley. Although the viticultural area is within the broader Napa Valley AVA, it is an entirely separate valley with its own watershed. The region encompasses 6000 acres and has a little over 1000 acres of planted vineyards. The majority of the arable land has been used.

One of the more conspicuous aspects of the valley’s terroir is its longer than average growing season. Budbreak occurs two or three weeks later than the Napa Valley average. Grapes are left on the vine for a longer time and can therefore develop very strong flavors and aromas.

Chiles Valley is best known for its old-vine Zinfandel. Many of these vines were planted before the Phylloxera Louse devastated much of California Wine Country in the late-nineteenth century. These ancient vines were saved by their isolation. They currently produce limited amount of highly prized grapes.

Recently planted Zinfandel vineyards also thrive in the AVA. Sunny days develop sugars while cool winds keep acidity at an advantageous level. The Zinfandels I have tasted from Chiles Valley Wineries tend to be quite fruity with supporting acidity and rounded tannins.

Soils on the valley floor are not overly fertile, but are also not entirely austere. They are alluvial and loamy. The fact that they are very well-drained is largely due to the existence of many creeks and watersheds in the AVA.

The vast majority of vineyards are planted between 800 and 1000 feet above sea level. The AVA is surrounded by steep hills that rise to about as 2200 feet. Hillside soils are extremely unfertile and made primarily of serpentine, sandstone and shale. Cool air from the tops of these hills is often drawn down into the valley’s vineyards.

Most fog from the San Pablo Bay is blocked by these same hills. The fog that does advance into the region does so later in the day than the majority of the Napa Valley. The fact that fog settles in the AVA later in the day gives it less time to burn off in the daytime sun. This can cause temperatures to drop relatively quickly after the sun goes down. The fog cover rarely advances over 1500 feet above sea level causing the AVA to normally be sunny.

The Impact of Terroir in Chiles Valley Wine Country

Along with Zinfandel, the abundant sunshine is also well-suited to Sauvignon Blanc and Cabernet Sauvignon production. Chardonnay is also grown in the AVA. It is usually made in a buttery, opulent style that is fuller-bodied. It is much closer to an Oakville rather than a Carneros Chardonnay. This is, of course, a generalization and exceptions exist.

Because of its relatively sheltered nature, winters tend to colder and summers hotter than AVAs on the Napa Valley Floor. During winter, it is not unusual for overnight temperatures to drop under 20 degress Fahrenheit, or for snow to fall above 1400 feet. Additionally, vineyards in the AVA can be succeptible to springtime frosts. At the same time, it rarely rains during the summer and days are usually very sunny and warm.

However, Chiles Valley is not entirely protected from external weather patterns and influences. Running northwest to southeast, the AVA is exposed to northwesterly winds. This breeze reaches the valley through its opening in the northwest. Additionally, adjacent canyons that run roughly east-west allow winds into the region to a lesser degree.

These winds are an extremely important feature of the valley’s terroir for several reasons. Depending on the time of year and the hour of the day, the winds can either moderate or exaccerbate temperature patterns. However, an almost constant feature of the breeze is its afternoon/evening duration and cooling effects.

On a hot summer day, the breeze moderates the AVA’s temperature. The afternoon winds also lower the air’s humidity. This feature of Chiles Valley terroir normally causes temperatures to drop more quickly after the sun sets, thus exaccerbating already cold nights. Lower humidity also lessens the risk of rot in vineyards.

While temperatures in Chiles Valley are more extreme than the majority of the Napa Valley Floor, they are more moderate than some nearby regions in the Vaca Hills. For example, Pope Valley (not an official AVA) is located to the north at a lower elevation and has higher mountains surrounding it. Because of these characteristics, wind and fog are almost non-existant in Pope Valley. Average temperatures are colder in the winter and hotter in the summer.