From a scientific point of view, the relationship between soil types and the resulting flavors in wine is not very well understood. There are certainly some general areas of knowledge (e.g. drainage and nutrition) but there are so many variables involved in grape growing that it can be difficult to understand what features exactly are responsible for what flavors. This leads to a proliferation of theories about the ideal soil for achieving certain flavors; some based expressly in science, some in mysticism, and a lot in clouded empirical experience.
Let’s work with science first. Empirical evidence suggesting a correlation between a flavor profile and a particular type of soil has been difficult to reproduce with similar soils in different locations. This is the bane of scientists. To be true, a process must be repeatable with the same result. There are far too many variables in a specific vintage in a specific vineyard to repeat an experiment and say for certain that it is the soil that results in a particular flavor from that wine. Over many years you can remove vintage variation and recognize a certain flavor component from a specific vineyard. But what about the clonal type of the variety? What about the climate at that vineyard? What about trellising and other farming practices? And we haven’t even mentioned winemaking interference. Minerality in a wine such as our Roussanne is probably not a direct expression of the minerality of our soil (our soil has high mineral content). No one can prove or disprove that. In our opinion, our climate may have more to do with the resulting flavor profile – well, climate and vine stress.
Let’s talk about vine stress because soil does have a role to play here. Vine stress induces concentration, intensification, and the complexity of flavors in wine. Vine stress depends on the degree of nutrient and water availability.
Our vineyard is part of an uplifted sea bed that was pushed into the air around 7-8 million years ago. You can find scallop and nautilus fossils in the soils. But despite this history, these are not the basic limestone soils of Burgundy. Millions of years of decaying forests have increased the pH of the soil so it is fairly neutral and is composed of a fine, silty, sandy loam, with a modicum of clay interspersed in the subsoils. It is high in inorganic matter, low in most nutrients. Its low nutrient content allows us to control the health and vigor of the vine, maintaining small but healthy fruit loads and keeping vigor in check.
With our high winter rainfall, our soils are well saturated at the beginning of the growing season. Being on a hilltop formed by a river gorge, our soil drains downward over the course of the growing season. There is no water table here as there are in most bottom lands. Water availability depends on the ability of the roots to penetrate the soil and to follow the water horizon as it recedes deeper into the earth. The fineness of our soil impedes the root progress, but not entirely, allowing for slow penetration of the top 4 or 5 feet of soil. By August, irrigation is necessary to maintain the right level of stress – too much stress, and the plant will shut down completely.