How does the soil composition affect the taste of wine?

The simple answer could be: same vine, change soil, different wine.

Your question is very interesting but partial being it only one part or the equation. The soil structure along with minerals in the soil, weather (water, temperature and humidity), altitude, exposition (sunlight and shadow), will make the fruit the way it will be, before the wine making process at winery. Sticking to the soil part, we should first understand what the soil (terrain) is and how it interacts with the roots of the vine.

The relevant factors are: How the soil originated, the climate in which the soil has developed, granularity and porosity of the soil.

The soils can be made: of the same composition of the one from which they originated (mother rock); by accumulation of deposits of organic type or by other type of soil as by accumulation due to the effects of winds, floods, submerged lands, etc.

The climatic zones contribute also to the composition, for example: in temperate areas, there are soils with several humid blackened layers and ferrous, others calcareous and rich in calcium carbonate. In very humid areas, brown and yellow soils, rich in iron, calcium and humus, in warm areas with low humidity, red soil rich in iron and aluminum.

How the vine get this nutrients is of interest as well. The soil of the surface, is the one used by the plants to develop their root system and as a source of nutrients. It is an ever-evolving element in which are present solid elements as rock fragments of varying magnitude and organic residues; liquid component as solutions circulating in the soil and gases, air, as well as other gas bound to the ground. These elements and their relationship define the level of habitability and fertility of the soil, which changes deepening and that can be divided in:

  • active, that is rich in organic matter and air, it is the layer where grower’s work take place, digging, application of fertilizers, etc;
  • inert which, though having the same constitution as the superior one, does not suffer from the workings and fertilizers, yet it is the layer in which the roots are most often developed.

From this set of characteristics depends the porosity of the soil or its granularity. The smallest part of these materials is of great importance because it is tied to the soil absorbing capacity. On these bases it has been found that siliceous and sandy soils give little colored wines but rich of delicate aromas. While in clay soils there are wines more intensely colored but less acid.

The vine root develops differently depending on the conditions described. A porous soil that favors the penetration of water and air, is a soft soil that facilitates root penetration and therefore the use of resources. Conversely, where the vine grows little, it feeds in a limited way.

For the above, absorption of minerals available in the soil, differs and contributes to the final product: nitrogen, which in poor presence makes the vine to develop few bunches of grape, in the opposite will reduce the level of sugar degree; phosphorus; potassium, which helps the sugar accumulation; calcium; magnesium which interferes with the ability to use iron by the plant, and so on.

To recap: even if the soil is of great importance, in the quality and quantity of wine produced by a vine, it is only due to the vine ability, to find balance between soil composition, minerals present in soil and vines, and the climate in which it develops, to return a great wine and all the nuances we taste.

(Elaborate from World wine encyclopedia – L. Paronetto)