Terroir and Grapes
By: Olga Stepina
Experienced wine tasters can tell the soil composition and environment in which grapes were grown based on the flavor of the wine alone. This kind of environment is called a terroir—a mix of climate and geographical factors, the most important of which is the mineral content of the soil, its power. This power is not determined by the fertility of the soil in the regular sense as the technical power of grapes requires its own special conditions.
Grapes are unique not only because they’ve allowed humanity to enjoy wine for centuries on end—the plant in itself deserves serious and in-depth study, from genetic and varietal specifics to the character and distinctness of different vines. Grapes naturally have a character that is second to none on our planet.
Here’s an interesting story: while all plants cultivated by humans require special conditions and energy input to grow and bear fruit (fertile soil, watering, additional fertilization, extra shade or sunlight, etc.), grapes still manage to stand out from the crowd. While they do, of course, require special conditions, their lives hardly depend on the hard work of humans.
It’s almost as though grapes allow people to use them—but only those who can hear and understand their strict and refined nature and who can work with a vine to help it perfect itself and build up its vigor. Grape berries are simply the result of all this work, the result of the vine’s tension and vibrations. And no matter how advanced modern technologies are, no matter what we do with additives and wine processing techniques, you will never get amazing wine from poor grapes!
The science of winegrowing has allowed us to accumulate sufficient knowledge about the requirements for working with grapes. Scientists create tables charting the origins of different grape varieties, they try to decipher the wine genome, they review the specific conditions of the areas around different varieties, and they study the effects of fertilizers on grapes and the correlation between the quality of berries and the age of vines.
This work even incorporates studies of moon and planetary cycles and the influence of music and ancient rituals on grapes. Nevertheless, one of the main prerequisites for strong grapes is their connection to the soil via the terroir in which they grow. Just as the Celts were once obsessed with finding and capturing particular water resources—springs—today’s top winemakers are hunting down lands with «golden» terroirs for growing grapes. Both cases require real magic—a rare confluence of multiple circumstances that, when combined, create the special formula for making wine of exceptional quality.
Characteristics of Soil Profiles
When analyzing soil material, people generally speak of two groups of minerals: primary minerals that transitioned to friable rock from magmatic and metamorphic rock without changes, and secondary minerals, which developed from primary minerals as a result of climate and biological factors. The correlation between primary and secondary minerals is what determines the chemical composition of the terroir.
Primary minerals include quartz (SiO2), oxides (rutile TiO2 (0.3%–0.5%), magnetite Fe3O4 (0.5%–1%), hematite Fe2O3), silicates—augite Са(Mg,Fe,AI)[(Si, AI)2]O6; hornblende Ca2(Mg,Fe)4(AI,Fe)[(Si,AI)4O11]; olivine (Mg,Fe)2SiO4, feldspars and mica, primary phosphates (apatite), and minerals that contain rare and dissipated chemical elements (Cu, Cr, Co, Mo, etc.). Stable primary minerals make up the framework, the backbone of the soil, while unstable ones transform over time and become the foundation for secondary minerals.
The amount of primary minerals influences the main agrophysical qualities of the soil, as apart from producing secondary minerals, they also act as a reserve of ash constituents for plants’ nutrition. Soils that contain primary minerals are friable, highly air and water permeable, and have a low water retention capacity.
Secondary minerals develop in soils in a number of different ways: for instance, through the crystallization of solid minerals from a solution (halite (NaCl), mirabilite (Na2SO4∙10H2O), gypsum (CaSO4∙2H2O), sodium bicarbonate (Na2CO3∙10H2O), calcite (CaCO3), magnesite (MgCO3), dolomite (Ca,Mg)(CO3)). These minerals determine the soil’s salinity level, its calcium carbonate, and gypsum content.
The crystallization of amorphous solids provides soil with minerals from the oxide and hydroxide classes (oxides and hydroxides of silicon (2SiO2∙nH2O), aluminum (AI2O3∙nH2O), iron (Fe2O3∙nH2O), and manganese (MnO2∙nH2O)). The high iron content of this group of minerals gives soils yellow, brown, and red colors.
Hydrolysis, hydration, dehydration, and redox reactions create the clay minerals that make up the majority of friable rocks and soils. These minerals are from the montmorillonite group (montmorillonite, nontronite, sauconite, saponite) that determine the soil’s absorbing power, cation absorbing capacity, soil swelling, high viscosity, water conductivity, and maximum hygroscopy. The group also includes kaolinite minerals that enable the adequate water conductivity and slight viscosity of the soil. It includes hydromicas that ensure proper potassium and magnesium nutrition for the plants; chlorites rich in magnesium (up to 31%), iron, and aluminum as well as manganese, nickel, copper, zinc, lithium, and other elements. Allophanes and amorphous substances are responsible for soil plasticity, water retention, cation absorbing capacity, soil swelling, and soil cohesion.
As such, mineral content and composition determine numerous important qualities of the soil: absorbing capacity, hydrophysical characteristics such as soil swelling, viscosity, plasticity, filtration, etc., the availability of macro- and microelements, the ability for nonexchangeable adsorption of potassium and aluminum, the activities of different microorganisms, and the activity of enzymes.
Characteristics of Soils for Winegrowing
All grape varieties choose unusual terroirs—soils of a stony, silicate, schistose, or gravelly nature, sometimes with granite, obsidian, and volcanic rocks. Such compositions would probably scare away any farmer, but these infertile and poor soils are where grapes can truly develop and strengthen.
One of the reasons why is that grapes don’t like water stagnation or the roots not having access to air: it causes decay of the root system as well as diseases and incorrectly developed grape flavor. Limestone or chalky soils, common in Europe, have good drainage and are able to rid themselves of any excess water. Such soils warm up and ventilate better, which in turn enables the grapes to grow faster and gain strength.
Scientists have conducted a sufficient number of studies to understand the influence that different kinds of soil have on grapes. They have discovered, for instance, that terroirs with high iron content are the reason why grapes can go black, which then causes the wine to be slightly cloudy—something that can’t be resolved in the winemaking process. Soils high in boron can promote faster ripening and high sugar content in grapes, but they also increase their alkalinity.
An excessive amount of potassium also increases alkalinity, and an abundance of phosphorus produces wines high in iron. Grapes also don’t like soils with a high sand, silt, or clay content. Sand does not retain water, and such soils are subject to drastic temperature differences at night and during the day; clay soils have low ventilation and low water-transmitting capacity; silt soils can contain a lot of humus, which causes plants to overgrow and exposes them to diseases and pests.
The favorable soil pH for grape cultivation differs in different parts of the planet. In Europe, for instance, the best grapes grow in slightly alkaline soils (such limestone makes grapes richer in potassium and magnesium), while American and South American grapes prefer slightly acidic or pH-neutral soils.
To get the nutrients the plant requires, grape roots can go as deep as 1.8 m. There have been cases of roots going as deep as 3.7–4 m, and even up to 15 m on rocky soils in the south of Europe. Specialists say, however, that root branching is more important than how deep the roots go.
The roots of a strong grape tree can reach 6–10 m in diameter and intertwine with nearby plants. Another interesting fact was discovered fairly recently: apparently, you need to wait at least three years before planting young grapes where an old tree has been uprooted. Grape roots have been found to produce chemical elements that affect nearby plants—their way of staking a claim to the territory. Those chemical elements continue to do their job even after all the old roots have been extracted.
Foundation of a Strong Vine
Smart winegrowing means satisfying the needs of a vine to the maximum and understanding the specifics of the terroir. Only then can winegrowers learn to approach grapes as living—perhaps even sentient—beings, and only then will they be able to «hear» the character of the soil and the «breathing» of the terroir. That’s when the magic happens, and the powers of nature and plants merge into one to create proper wine.
We currently know that grapes require over seventy different minerals and nutrients (although the list is not exhaustive and sees frequent new additions). Nitrogen, calcium, potassium, phosphorus, magnesium, zinc, iron, boron, manganese, sulphur, and other elements are some of the components in the complex cycle of the grapes’ growth and fructification. Appreciating the fine work of every part of this mechanism is what allows people to manage this process and get high-quality wine in return. And the ancient understanding that the right terroir is the most crucial component for winegrowing is still true today, regardless of the scientific and technological milestones we’ve achieved.