- Discover soil to better understand wine -
I have sat through quite a few wine presentations throughout my career and soil is always mentioned as a key factor during the description of a wine. But, I must admit, normally during these presentations, soil is not given enough credit. Too often, soil is glossed over as a factor and its importance on how it affects the final result in wine is not explained adequately.
The purpose of this article is to understand soil better and how it relates to the wine we drink. In fact, soil is one of the most essential aspects to consider when talking about wine. When deciding which variety of grapevine is more suitable for a certain area, agronomists spend a lot of time analyzing soil composition, as well as other key factors such as altitude, aspect, sun exposure, temperature, rainfall percentage and proximity to a water body.
SOIL AND WINE QUALITY.
In terms of soil and wine quality, we often assist in a debate between two different schools of thought.
From one side, we find supporters of the opinion that climate is more important than soil. This approach is very common in the new world wine industry; in fact, new world opinion has tended to minimize the role of soil, considering instead the climate to be much more relevant. As an example of this outlook, we can look to Amerine and Winkler’s 1944 climate classification of California in V (five) zones.
Meanwhile, in the old world, wine experts have a distinctly different approach. There, soil is considered an essential element, and in France, for instance, soil was used to create the concept of a Terroir, (see Burgundy).
When it comes to talking about soil and wine, the very first concept to keep in mind is that the most suitable soil for grapevine cultivation is less-fertile soil.
Less-fertile soils encourage the vine to produce less vegetation (i.e. leaves) and fewer grapes which means that the grapes that do grow will be more concentrated. Berries will not become over-sized, so their skin to pulp ratios remains high, and the pigments and flavor compounds (largely present in their skin) are not diluted. In fact, quite often we read that vines have to struggle for nutrients and water; technically this is considered “vine stress.” It is very important to be able to manage vine stress because, when done correctly, it can lead to higher profile grapes.
Soil is important for two mains reasons:
water supply;
temperature control.
Water supply: this term generally refers to the soil’s ability to retain the right quantity of water for the vine.
To much water would probably stimulate vines to produce excessive vegetation. However, don’t forget that this factor has to be combined with the climate present in a specific wine region and the aspect of the vineyard.
For instance, if you are in the South of Spain or in certain AVAs of California, you definitely need your vineyard soil to perform a great ability to retain water. In cold areas, you’d rather have a darker soil that can retain the heat.
Temperature control: soil is also a key factor in controlling the temperature in the vineyard. Temperature in a vineyard has a great effect on the sugar-acid balance in grapes and helps to determine the quality of the resulting wine. For instance, dark-colored soils absorb light and have the ability to convert it into heat. It is a suitable choice for areas where sunlight is low and is often cloudy.
The presence of stones inside the soil or on its surface influence both mentioned circumstances; this is because a high proportion of stones can ensure good drainage and if they are located on the surface, they can reduce the water evaporation.
Ultimately, the best soils for wine quality are:
. moderately deep to deep;
. fairly light-textured, often with gravel;
. sufficiently high in organic matter to ensure soil friability and good worm population;
. overall, relatively infertile, supplying mostly mineral elements for healthy vine growth.
DIFFERENT TYPES OF SOILS AND PECULIARITIES.
One of the basic principles in growing grapes for winemaking is to force the vine to develop a large underground system of roots, that deliver an ample supply of minerals and nutrients to the growing leaf system. Soil is key in developing this root system.
However, we need to remember that a soil in a vineyard is almost never a uniform type; it is always a mix of soil types with a mix of different soil elements. This soil mix, when matched with the right climate, can create the perfect context (aka terroir) suitable for specific types of wine production.
We will see how difficult it is to break soil down into singular categories. However, we can start by saying that we can divide soil into 3 distinct classes: igneous soil, metamorphic soil, and sedimentary soil.
Soil can be categorized also based on texture and in fact, the 3 most common types of soil suitable for grapevine cultivation are: clay, silt, sand. Loam, which is basically a mix of the other 3 types with the addition of humus is generally speaking a bad choice but it is also true that its level of suitability changes according to the quantities of the other 3 types.
Gravel: this type of soil is one of the most iconic characteristics of the left bank wine regions in Bordeaux (Ch. Haut-Brion).
The vineyards of Graves are characterized by their gravelly surface. Such soil offers excellent drainage, imposing on the vine the slight water stress favored for the resulting wine’s high quality. It is also well known that gravel is quite infertile.
Alluvium is a type of sediment which can be described as alluvial; related soils are often fine grained and typically fertile. Where these soils are stony and sandy they are highly valued for viticulture. Examples of this are the Médoc region in Bordeaux and Marlborough in New Zealand.
Chalk and Marl are two distinct types of soil, both very suitable for viticulture.
Chalk is a type of pure white limestone. It can ensure excellent drainage, combined with the capacity of the subsoil to store substantial amounts of water. Pure chalk is of low fertility, resulting in a rather low vine vigor and naturally good canopy microclimate.
Marl is a combination of limestone and clay, and it can perform a good drainage as well as display a powerful ability to retain heat. It is typical in Jura, in the vineyards of Beaune and Pommard. It seems to be more suitable for white varieties because it can help to ensure salinity and acidity in wines.
So what did we learn here?
Soil is an essential element in winemaking but it needs to always be considered in relationship with the climate in which it is found. And, in fact, in colder, rainy, and cloudy climates, metamorphic and sedimentary soils are generally a better match for viticulture. Meanwhile, in warm and sunny areas, clay and sand are the most suitable soil types for grapevine cultivation.
Sand is the wild card; it can perform differently in different soil scenarios. In fact, in some areas sand can be suitable for white varieties while at the same time, in other areas, especially when mixed with gravelly stones, it can make for great red varieties.