Next to climate and grape variety, one of the most important factors influencing the quality of wine. The different soil types have developed over millions of years through physical and chemical weathering of rocks and through humification of organic matter. During physical weathering, natural forces such as wind, water, heat, cold and ice first cause the rock formations to be mechanically broken up into pebbles and gravel. Strong temperature contrasts, friction and shear forces as well as frost splitting by frozen water in rock fissures play an important role in this process. Chemical weathering processes such as oxidation, solution processes and acid attacks attack the mineral lattice structure of the rocks. In the process, easily water-soluble minerals such as carbonates and sulphates are first dissolved, and the rock slowly decomposes into grime, sand, silt or clay. Every rock, even the hardest granite or quartz, will eventually disintegrate into dust, even if it takes many millions of years.
Organic substances from plant residues, animal residues from worms, insects and small animals of all kinds as well as dead microorganisms such as algae, bacteria and fungi are converted into humus. In the process, nitrogen compounds essential for plant growth (nitrate, ammonium) and other nutrients are released. Fungi and bacteria play the main role in the decomposition of organic residues such as wood, leaves, roots or animal carcasses. Insects such as soil mites are important because of their crushing feeding activities. Earthworms play a decisive role in soil loosening, mixing and the formation of stable clay-humus complexes, which are formed in the earthworm gut and excreted as faeces. These contribute to the structural stability of the soil and can bind easily water-soluble nutrients and thus make them available to the plants for a longer time.
Every soil consists of soil horizons (soil layers) with special properties. They are almost always horizontal and can be seen in the soil profile (vertical section of the soil in an excavation). The sequence is the essential criterion for determining the soil type. From top to bottom, a soil is divided into an organic soil horizon or H-L-O horizon (peat from plant remains, litter) and a tripartite mineral horizon. These are the A horizon (mineral topsoil with an animated, humus-rich layer), the B horizon (mineral subsoil with a humus-poor layer with fine soil already chemically weathered to sand, silt or clay) and the C horizon (little changed source rock with physical weathering). Horizons are mixed by deep mechanical soil cultivation. Depending on the climate and the effects of erosion, the A or B horizon may also be missing or only marginally formed.
In a vineyard, the horizons have usually already been mixed up by tillage(rigoles). Rocky subsoil, initial soil, soil cultivation, fertilization as well as water balance with a well-balanced ratio between water storage capacity and water withdrawal characterize the vineyard location in addition to the local climate (microclimate or site climate) and give each vineyard site the typical and unmistakable character of its origin. The duration of the vegetation cycle, the direction of exposure (sunshine) and the local climate on the slope, the existing soil conditions, the humus and lime content and the water supply influence the choice of the most suitable grape varieties.
The well-known geologist and wine book author James E. Wilson aptly writes in his book "Terroir - Key to Wine": "The soil is the soul of the vine". However, the direct relationship between rock, grape variety and wine character is probably only marginally pronounced today due to the uniform use of often flat-rooted rootstocks with heavy mineral fertilization and the use of new winegrowing cellar methods. In the vineyards, which used to be only sparsely and mostly organically fertilized, with their old vines, planted true to their roots and often rooted deep in the rock, this relationship was certainly much more pronounced.
The French, in particular, recognised the importance of the interplay between climate, rock, soil, location, microclimate and grape variety at a very early stage and made this, so to speak, their philosophy in creating the term terroir. The terroir and the grape varieties suitable for it are defined by wine law in the classification of the wine-growing regions as Appellation d'Origine Protégée (AOP). This is a clear difference to the philosophy in Germany and Austria, for example, where great (too much) importance is attached not to the location but mainly to the grape variety and the vintage wines made from it.
In terms of wine quality, it can be of great advantage if the vines have to bore their roots as deeply as possible into the soil because of stony ground. The ability of soils to act as ion exchangers, i.e. to exchange nutrient salts in the soil solution for the protons (H+) and anions (OH-) emitted by the plant, is what makes it possible to supply the roots with essential nutrients and trace elements in the first place. The minerals absorbed are found in the total extract of a wine. The vine needs about twenty essential trace elements and the main nutrients in order to thrive optimally. As a permanent crop it is less dependent on fertile soil than annual crops. It is not unusual to find sites with very poor soils on which high-quality wines grow. However, this does not mean that the less nutrients are available in the soil, the better the wine quality.
A lack of nitrogen and amino acids in the must can hinder the yeasts during fermentation and cause fermentation errors. Among other things, this can manifest itself through the wine defect UTA (atypical ageing tone). Rather, the harmonious composition of the nutrients in the soil, the availability of water and nutrients as well as the aggregate state and rooting are important for the suitability of a soil for viticulture. By plant or soil tests using the EUF method, a lack of nutrients can be detected and, if necessary, remedied by fertilisation. A comprehensive classification or the determination of the soil quality for agricultural use in general or especially for viticulture is carried out by means of an assessment.
In calcareous soils with pH values above 8, the high calcium content of the soil makes it difficult to absorb other doubly positively charged ions such as nitrogen compounds, magnesium or the trace elements boron, iron, manganese or zinc, so that lime-chlorosis or other physiological deficiency symptoms can occur, even if the soil normally contains sufficient nutrients. Especially at the beginning of the growth cycle, the nitrogen content (in the form of nitrate and ammonium) in the soil should be sufficient. As a general rule, basic (alkaline) soils with a high pH above 8 (for example, lime, chalk and marl soils with mostly high levels of calcium and magnesium) produce wines with a higher acidity, while acid soils with a low pH below 6 to 4 (for example, granite, quartz sand) produce wines with lower acidity. Tests with increased potassium additions have shown that vines react with increased malic acid production. To compensate for the increased influx of positive potassium ions, the plant produces negatively charged acid anions (malic acid). However, there are of course other causes of acidity in wine (independent of the vintage or ripeness-related acidity values).
A good vineyard soil should be lean, medium to deep, well aerated, permeable to water and not compacted, rich in content but not too fatty, not too rich in humus but rich in mineral components. The best sites are so-called hillside locations, because this creates an almost vertical angle of incidence for the sun's rays in late summer, allowing the maximum amount of sunlight to be used. The best location on a slope is the wind-soothed concave centre (belly, navel, kidney), where the highest temperature sums are reached and the soil is usually well permeable. The colour of the soil also plays an important role, because dark soils absorb the sun's heat faster and more comprehensively, while light soils reflect light, so that such soils do not heat up as quickly or as much. The suitability of an area for viticulture is called winegrowing suitability, which can be determined on the basis of a catalogue of criteria.
Alberese: Italian name for weathered sandstone with a high proportion of calcium carbonate (limestone) in Tuscany, which is mainly found in the central and southern part of the Chianti region
Alluvium/Alluvion: Alluvial sediment (loose materials) deposited by water. Alluvium is also another name for the Holocene, the youngest and since the end of the last Ice Age about 10,000 years ago until today's time. Alluvial soils are mostly fine-grained, very fertile types of soil that are formed in the flood and estuary areas of rivers. They consist of soil particles that are washed up and sedimented when the water calms down.
Depending on the sinking speed of the soil particles carried in the water and the flow velocity of the flood water, they consist of clayey silt, silt, sand or, in the immediate vicinity of the shore with high flow velocities and strong erosion dynamics, of gravel and boulders. Despite the predominantly stony and sandy nature of the soil, as for example in the French Médoc, these soils are very suitable for viticulture. The secret of the sites there are the clay lenses deposited during various floods and covered with sand and gravel inside the alluvial gravel terraces, which can store water. Such layers of clay are literally sought by the vine roots.
Amphibolite: Mostly black over grey to dark green rock, formed by the metamorphic transformation of basalt (see below) under high pressure and temperature conditions. It consists of up to 50% representatives of the amphibol group, such as hornblende (see below) or chermakite, and up to 40% of other minerals such as garnet and quartz, as well as ores such as magnetite and pyrite.
Aeolian: Phenomena caused by the wind and named after the Greek wind god Aeoleus. Aeolian transport causes fine material such as loess, silt (silt) or clay to be released from the source material such as loose rock and transported by the wind over greater distances. Aeolian weathering is the removal of rock by grains of sand, fine gravel, etc. moved by the wind with the effect of a sandblaster. This creates an aeolian weathering soil.
Arkose: The geological term describes a pink to reddish, coarse-grained sandstone with a high proportion of feldspar, which occurs mainly in dry areas with little water. It leads over to the coarser-grained granite rocks.
Alluvial soils: Soils formed from river deposits which are periodically flooded. Such soils occur, for example, in the Danube, Moselle and Rhine floodplains. When they are no longer flooded, they develop into brown and parabrown soils. These soils are mostly rich in nutrients, biologically active and fertile.
Basalt: Basic effusive rock (cooled magma) consisting of feldspar, hornblende, olivine and magnetite. It contains much lime and soda and is rich in minerals. The hard, slowly weathering rock forms good soils and produces wines with appealing acidity.
Pumice (pumice stone, pumice tuff): The porous, glassy volcanic rock is formed by gas-rich volcanic eruptions in which the lava is foamed by water vapour and carbon dioxide. It is chemically indistinguishable from other lava, but is much lighter due to the trapped air. The colour varies from black and with increasing air content over grey to white. The term pumice tuff refers to the grain size, at least 75% must consist of volcanic ash. Soils made of pumice have a good water retention capacity and are very suitable for viticulture. They are found throughout the Greek island of Santorini, which was created by a volcanic explosion. Similar to pumice is obsidian, but it contains much less carbon dioxide. See also under Canava and below at volcanic rock.
Blue shale: See below for slate.
Boulbènes: A term commonly used in Bordeaux for a very fine, siliceous soil. It is found for example on the plateau of the Entre-deux-Mers area.
Brown earth: These A-B-C soils develop mainly over calcareous but base-rich rocks such as granite, gneiss, greywacke, clay slate and clayey sandstone. The formation took place under humid climate conditions from humus-rich topsoils on low-calcare silicate rocks (ranker - see below) with deciduous and mixed forest cover. The brown colouring in the B-horizon is caused by iron oxides, which are formed during the chemical weathering of iron-containing silicates. The acids emitted by the tree roots strongly contributed to the deep weathering of the B-horizon. Lime content, stone content and water balance of brown earths can vary greatly. Depending on its composition, this can be an excellent soil for viticulture.
Parabraunerde differs from brown earth in that clay particles have been shifted from upper to deeper layers. This is a process that takes place during soil acidification. Cementing lime structures disappear by lime solution, so that the released clay particles are washed away with the seepage water into deeper soil layers. Parabrown soils were mostly formed from pararendzinas. Parabraun and brown earths are the most common soils in humid Europe. Loam and loess parabrauner soils are among the most fertile soils.
Breccia: conglomerate with angular components (see below).
Coloured sandstone: Coloured, mostly red sandstone with partly clayey alluvium. The mottled sandstone was formed from the erosion debris of the mountains of the Palaeozoic period. It was deposited in a dry semi-desert climate in a large basin (Germanic Basin) in the middle of present-day Europe and was later overlaid by sedimentary rocks such as Jurassic limestone or by rafts.
Iron: See under Terra Rossa and further down at Rotliegendes.
Feldspar: Complex silicate compounds of white and reddish minerals, which account for about 60% of the composition of the earth's crust. These contain iron, potassium, calcium and sodium. There are three main groups: potassium feldspar (adular, sanidine), soda lime feldspar (albite, periclin, anorthite) and microline. Weathering produces clay minerals rich in bases, which can release mineral-bound ions as nutrients to the vine. Feldspar is one of the three main components of granite and gneiss - see below.
Flint: The grey to black coloured rock (flint, silex) of the fine crystalline quartz type chalcedony with a splintery-mushy fracture has a white, porous surface structure. It originates from silicic acid-containing marine life (diatoms, radiolaria = marine plankton - see also diatomaceous earth). This soil produces typical wines with a taste of flint like the French Pouilly-Fumé.
fluviatile: eroded or deposited by flowing water - the result is alluvial soil; see above.
Flysch: Fossil-poor sandstones as well as marl and clay...