The Importance of Soil and Geology in Tasting Terroir with a Case History from the Willamette Valley, Oregon

Abstract

Wines differ from each other based on seven different factors: the type of grape, the bedrock geology and resulting soils, the climate, the soil hydrology, the physiography of the site, the winemaker, and the vineyard management techniques. The first five of these factors make up what the French call terroir, “the taste of the place.” An important process is the bedrock weathering into soils which then liberate chemical nutrients to the grape vines. Twelve of the sixteen essential elements for wine grapes come from the soil. Soil physical characteristics, such as soil depth, pH, drainage, salinity, color, and particle size, can affect the quality of grapes. Control of vigor in the plants is so important and is accomplished through irrigation or the use of poor soils. Certain grapes do better on different soils; therefore, it is apparent that all around the world, the geology and soils make up an important component of the terroir of the wine. In the Willamette Valley of Oregon in the United States, the terroir is strongly influenced by the bedrock geology and soils. The two dominant groups are the volcanic soils, the Jory Series, which developed on the Columbia River Basalts, and the Willakenzie Series, which developed on uplifted marine sedimentary rocks in the foothills of the Oregon Coast Range. The wines made from the grapes of these two soils are very different – so different that the Willamette Valley AVA has been subdivided into six new American Viticultural Areas based primarily on terroir.