© 2019 Russian River Valley Pinot Forum

the fog

"Support materials - Incredibly good! The soil-type map and the fog flow chart I'm going to scan and use for my Sommelier classes."
 

In the Russian River Valley, the fog is the dominant factor that defines the appellation, as well as the style of the wines from here. From the Pacific Ocean to our west, fog creeps in primarily along the Petaluma Wind Gap, an area south of Bodega Bay near the Marin County line with low elevation and soft rolling hills that provides an easy conduit into the western part of Sonoma County.

 

During the warm California summers, the interior San Joaquin Valley becomes extremely warm, many days over 100 degrees. This intense heat causes an offshore movement of cooler air over the Pacific Ocean to migrate eastwardly through Sonoma County. The high humidity air condenses as it passes through the Petaluma Wind Gap and into the northern part of Russian River Valley. The process usually begins by mid-afternoon and by 7 or 8 o'clock, you can actually see the fog "rolling over" the city of Sebastopol toward Santa Rosa and Healdsburg, settling into the low-lying vineyards and slowly climbing up the hillsides, before reversing its steps late the next morning.

 

The fog provides several benefits: In the summer, the daytime temperatures can exceed 90 degrees, while at night it can dip into the 50s. This dramatic shift in temperature sets up a series of metabolic changes in our grapes which result in the creation of the sumptuous texture for which our area is famous.The cool, airy blanket the fog provides also protects the vines from all-day heat which can cause dehydration in the warm summer months, and allows the vines' roots the necessary time to absorb needed moisture from the soil. It also allows the natural acidities to remain balanced within the fruit. Another benefit of the fog is the diffusion of sunlight and UV rays: as flavor development is achieved during a growing season, many of the chemical compounds within the berries and skins are produced by direct reactions from various wavelengths of UV light. So, one wavelength may cause an ester formation of the flavor raspberry, while a different one may cause from the same ester formation the flavor of blackberry. The fog has a significant influence on the flavors we believe are unique to pinots from the Russian River Valley.