Soils Impact on Wine

How does soil influence wine quality?

Regardless of the region or the varietal, wine quality is the sum of a wine’s intensity, complexity and balance.  Wine lovers and romanticists often describe that they can taste the soil in the wine.  While such declarations may be scientifically challenged, it is clear that soil has a direct impact upon wine quality in three major ways.  First, the physical properties of the soil impact water holding and rooting capacity.   Second, the chemical composition of the soil influences plant growth and development.  Finally, the biological status of the ground impacts pest and disease pressure upon grapevines.  Thus, the physical, chemical and biological composition of a soil proves that it is more than merely “dirt” and is dynamically linked with wine quality.

The best wine growing sites in the world are said to have well-draining soils with adequate water-holding capacity, lighter soil texture which is less prone to soil compaction , moderate depth and low relative level of fertility.  While it is as impossible to find a perfect soil as it is a perfect wine, it is definite that soil impacts wine quality greatly.  The depth and water holding capacity, surface structure, chemical and microbiological composition all can increase or decrease wine intensity and concentration, complexity and balance.  Fortunately wine quality is also impacted by a variety of factors other than soil such that finding a perfect wine may in fact be easier than simply finding the perfect soil.

How does Soil Influence Wine Intensity?

We all have an opinion on how intense we want our wine to be, but do we know what factors can influence the intensity of wine? The intensity of a wine can be measured by the concentration of phenolics such as color, tannins, aromas, and flavors.  High-quality wines are said to have high intensity and concentration while low-quality wines are watery and weak.  The amount of water taken up by a vine has a direct impact on the development and progression of these phenolic compounds.

A 2009 Bordeaux vintage study, completed at the University of Bordeaux, found that good vintages and higher quality wines were based upon water deficit at ripening rather than climate. Which means, in such a region as Bordeaux wherein irrigation is strictly prohibited, the physical soil structure is intimately associated with quality.

Thus, wine quality is more greatly affected by vintage and soil types there than in a New World region such as Napa, California where irrigation may be utilized to minimize some of the effects of vintage and varied soils.  This is the case at Stag’s Leap Vineyard where the distinct soil types are managed as accurately as possible such that all blocks are watered on an “as need” basis.  This permits berry size to remain small yielding wines that are more concentrated and complex.

Got Nutrients?

Just like with us, nutrients play a very important role in the health of a vine. The nutrient exchange of a vine and its soil, impact the vine’s health and overall development. Vines need macro and micro nutrients and their uptake depend not solely upon their amounts, but their availability in the soil. The cation exchange capacity (CEC) and pH are both measurements of nutrient availability, slightly acidic (pH 6.5 to 7) and low pH soils have better nutrient availability. Lack of nutrients can lead to poor growth and decreased fruit production. High soil pH can lead to an increased risk of potassium, which could reduce the wine’s fruit aroma and give it a soapy feel in the mouth. This can also be correlated with increased vine disease and drought which is the cause of many unbalanced high pH and high Titratable Acidity (TA) wines.

Winemakers are able to add some tartaric acid, as is commonly done by boutique producers, however rarely can enough acid be added to compensate for the higher pH without producing an overly acidic and bitter wine. Conversely, regions such as the Willamette Valley, in Oregon, have high nutrient levels, particularly nitrogen which will lead to increased vegetative growth and flavors. To increase wine quality, vignerons install drainage tiles that decrease water. Vignerons have also adopted vertically divided canopy systems to deal with high nutrient uptake, which also minimizes the shading of fruit- which leads to lack of balance and complexity.