About an hour northeast of San Francisco is the picturesque town of Sonoma, California. The western border joins the Pacific coast, while the Mayakamas Mountains rise on the eastern borders.

Here, 18 American wine regions (AVAs) offer a variety of microclimates. More than 400 wineries produce everything from spicy Zinfandel to fruity Pinot Noir.

This vast region has many different soil compositions, making it a fascinating study of geography and topography. Grape growing in Sonoma can be very different from the area you are in.

Agoston Harashti, responsible for the early planting of European vines in Sonoma/Alama Agoston Harashti, responsible for the early planting of European vines in Sonoma-Alama

Brief history

The history of Sonoma wine began in the early 1800s when Russian settlers began planting vines along the Pacific coast. Ten years later, quantitative grape growing began at the mission of San Francisco Solano. In a Mexican mission, thousands of vines were planted, which were used for religious purposes. The plantations grew, but it was not until the mid 1850s that the first unsaleable grapes were grown in Sonoma.

The Hungarian Count Agoston Haraszti, attracted to California by the gold rush, then bought the Salvador Vallejo vineyard in the Sonoma Valley. He planted vines from France, Spain and Italy. This winery would later become a winery in Buena Vista, setting a precedent for European-style wines throughout the Sonoma-district.

Spring vineyard in the Rockpill Hills, Sonoma / Alamia, near Hillsburg, California.

Sonoma Head TAA

Many geographical characteristics determine the production of Sonoma wine. One of these is the maritime influence of the region from the neighbouring Pacific Ocean. The height of the Mayakamas is just as important as the fog hanging over the valley floor. Each ABA deals with one or more of these growing conditions, some of which are considered natural resources by the winegrowers.

In the microscopic Funtaingrove area, the East Central AVA, which is also the second youngest AVA in Sonoma, can reach altitudes of up to 2,000 feet. The grapes also benefit from the marine influences of a nearby mountainous area of Santa Rosa. In Fort Ross Sea View, also under the influence of the ocean, vineyards are planted on top of round, often darkened 1000 feet high ridges.

In the green valley of the Russian river, which flows into the wider, central valley of the Russian river AVA, the fog rises at the bottom of the valley. This is good for Chardonnay and Pinot Noir, two species that need the sun to ripen but also prefer cool nights.

Fog is an important part of our microclimate, says Joy Sterling, partner/general manager of Green Valley’s Iron Horse Vineyards, which is dedicated to sparkling wines. A major advantage is that the temperatures required for growing Chardonnay and Pinot Noir are lower for the bubbles and for Pinot Noir in general.

The coastline of Sonoma is a large AVA, into which the Russian river valley flows. Fog plays an essential role in this, because it promotes enormous temperature fluctuations. At night, this can lead to falls of up to 40°F, preventing Chardonnay and Pinot Noir from dominating and having too high an alcohol content.

The climate here is due to the Pacific Ocean, says Craig McAllister, the head winemaker at La Crema Winery, who has vineyards in the Russian river valley, Carneros and the wider Sonoma AVA coast. The change in daytime temperature – the difference between high and low temperatures during the day – plays an important role in the accumulation of sugar, the development of colour, taste and aroma, and the maintenance of a balanced natural acidity.

The same applies to the Southern Carneros (also in the coastal area of AVA Sonoma), known from the chardonnay and pinot noir, and the smaller and more recent Petaluma Gorge, built by AVA Sonoma in 2017.

But all that fog can be a problem.

The downside is that too much fog can cause problems in the vineyard, which we have to soften with our cultivation methods, including intensive manual work such as pulling out leaves to allow more air to circulate around the grapes, Sterling explains.

Bennett Valley Vineyards, Sonoma/Alamas Bennett Valley Vineyards, Sonoma/Alamas

The Bennett Valley, in south-central Sonoma, is somewhat isolated. It is a small ABA with a cool climate, it is mainly known for its Merlot. This distinguishes it from other AVAs with a cool climate, such as in the valley, where Pinot Noir is grown, or in the mountain areas where Cabernet is grown.

Mount Sonoma and Mount Moon are two geographically close names, separated by the narrow valley of Sonoma AVA. Both are located southwest of Sonoma and are known for the Cabernet Sauvignon which is grown in the hills. So is Pine Mount Cloverdale Peak, although it is located in the northwestern part of the county, above Alexander Valley and AVA Knight’s Valley.

These colder microclimates make it possible to create expressive cabernets that differ in their characteristics from those found in the lower parts of the Napa Valley.

Warmer AVAs such as Sonoma Valley, Knights Valley, Alexander Valley and Chalk Hill tend to be more mature expressions. The producers benefit from the abundant sunshine and the well-drained soils of these regions.

AVA North-Sonoma includes Knight’s Valley, Alexander’s Valley, Pine Mountain-Cloverdale Peak, Chalk Hill, Russian River Valley, and parts of Green Valley and Rocks.

Another grape variety that benefits from the warmth of some of these AVAs is Zinfandel, which grows in the Rockpile Valley and Dry Creek and, to a lesser extent, in the Alexander Valley and Sonoma Valley.

River Sonoma / Getty River Sonoma / Getty

Sonoma Terroir

The soil of Sonoma can vary from sandy silt and volcanic ash to rocks, and this diversity can change the character of the grapes from one name to another.

The landslide of the Cretaceous, which borders the Russian river, got its name because of the chalk vein that runs through it. It is in fact volcanic ash that drains Chardonnay and Cabernet Sauvignons.

The green valley of the Russian river has a type of soil known as Golden Ridge which is very hospitable to viticulture.

According to Sterling, the soil in Golden Ridge is a sandy loam. Five million years ago, the Green Valley was an inland sea that slowly sank into the ocean, leaving behind a sandy subsoil. Okay, great chest tube.

Diversity practically defines Sonoma. That’s how the winegrowers talk about their land.

In La Crema we are looking for soils that can drain freely and give the vines relatively little energy, says McAllister. Most are sandy or silty loam, but some are also seen with a higher proportion of clay or gravel. The combination of climate and soil influences gives us complex, layered and balanced wines.

Because the terroir is very different from one AVA to another, there are about 50 different grape varieties in Sonoma. The most commonly grown varieties are Pinot Noir, Chardonnay, Cabernet and Zinfandel. Varieties such as Sauvignon Blanc, Vignier, Pinot Blanc and Syrah began to strengthen their position.

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