Winegrowers and winemakers seek to find the geological compositions and terroir that will grow the finest wine grapes. Many wine soils are defined by their textures, which are comprised of types of igneous, sedimentary and metamorphic rocks. The different soil textures produce different characteristics in wine.
- Sandy Soil has rock that has been pulverized into small particles. It is well-drained and retains heat. The wines have high aromatics, pale color and low tannin.
- Clay-Based Soil stays cooler and retains water. This texture produces muscular wines with structure, high extract and color.
- Silt/Loess Soil produces smooth and round wines with less acidity. These fine-grained soils retain water and heat. While this type can be too fertile, one good variety is loess, a type of wind-blown silt comprised mainly of silica.
- Loam Soil is nearly an equal mix of silt, clay and sand, as well as an organic matter called humus. Loam is very fertile and typically causes vineyards to be over vigorous, which can render wines that have little flavor or color.
- Gravel Soil can range from the size of a pebble to the size of a fist. Gravel drains freely, absorbs heat and reflects it onto grape varieties, particularly at night when temperatures drop. This is a good soil for Cabernet Sauvignon and other late-ripening grapes but can cause water stress in Merlot and other varieties.
- Alluvial Soil is comprised of a combination of clay, silt, sand and gravel that has been deposited over many years by running water. It typically contains a lot of organic material and is present in many of the world’s wine regions.
- Limestone Soil contains fossils of ancient marine life and is high in calcium. These soils can form impenetrable layers that block roots. The term “marl” describes a crumbly mixture of clay and limestone. The Cote d’Or region in eastern France contains a calcareous marl that produces good Chardonnay.
- Chalk Soil, a type of limestone, is soft enough for roots to grow in and is cool. It holds enough water to nourish vines, yet it drains well. Its calcium content makes it alkaline, producing grapes with a high acid content. Pure chalk soils are found in the famous Champagne region of France.
- Volcanic Soil is comprised of basalt and other rocks. Volcanic soils of Napa Valley of California have a high mineral content but hold little water; the vines lack vigor but are good for producing wine.