Next to climate and grape variety, one of the most important factors influencing wine quality. The different soil types have developed over millions of years through physical and chemical weathering of rocks and through humification of organic matter. In physical weathering, natural forces such as wind, water, heat, cold and ice initially cause the mechanical disintegration of the rock formations into clods and gravel. Strong temperature contrasts, frictional and shear forces as well as frost blasting by frozen water in rock crevices play an important role. Chemical weathering processes such as oxidation, dissolution 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 dissolved first, and the rock slowly decomposes into grit, sand, silt or clay. Every rock, even the hardest granite or quartz, will eventually crumble to 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, the nitrogen compounds essential for plant growth (nitrate, ammonium) as well as other nutrients are released. Fungi and bacteria play the main role in the decomposition of organic residues such as wood, leaves, roots or animal corpses. 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, making them available to plants for longer.
Every soil consists of soil horizons (soil layers) with special properties. They are almost always horizontal and can be recognised 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 three-part mineral horizon. These are the A horizon (mineral topsoil with a revitalised, humus-rich layer), B horizon (mineral subsoil with a humus-poor layer with fine soil already chemically weathered to sand, silt or clay) and C horizon (little-amended parent rock with physical weathering). Horizons are mixed by deep mechanical tillage. Depending on the climate and erosion impact, the A or B horizon may also be absent or only marginally developed.
In a vineyard, the horizons have usually already been mixed through soil cultivation (infiltration t renches). Rock subsoil, initial soil, tillage, fertilisation as well as water balance with a balanced relationship between the water storage capacity and the water drainage characterise the vineyard location in addition to the local climate (microclimate or site climate) and give each vineyard site the typical and distinctive character of its origin. The duration of the vegetation cycle, the orientation of the exposure (sunlight) and the local site 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 shallow-rooted rootstocks with heavy mineral fertilisation and the use of new viticultural cellar methods. In the vineyards that used to be fertilised only sparingly and mostly organically, with their old vines planted ungrafted and often rooted deep into the rock, this relationship was certainly much more pronounced.
The French in particular recognised the importance of the interplay of climate-rock-soil-site-small climate and grape variety very early on and elevated this to their philosophy, so to speak, in the creation of the term terroir. The terroir with the grape varieties suitable for it is 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 site but mainly to the grape variety and the single-varietal vintage wines produced from it.
In terms of wine quality, it can be of great advantage if the vines have to drill their roots as deep as possible into the soil due to stony ground. The ability of soils to act as ion exch angers, i.e. to exchange nutrient salts in the soil solution for the protons (H+) and anions (OH-) given off by the plant, is what makes it possible in the first place to supply the roots with essential nutrients and trace elements. The minerals absorbed are found in the overall extract of a wine. The vine needs around twenty essential trace elements and the main nutrients to thrive optimally. As a permanent crop, it is less dependent on fertile soils than annual crops. It is not uncommon to find sites with very poor soils where high-quality wines grow. However, this does not mean that the fewer nutrients 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 faults. Among other things, this can manifest itself in the wine defect UTA (atypical ageing tone). Rather, the harmonious composition of the nutrients in the soil, the water and nutrient availability as well as the aggregate state and rootability are of importance for the suitability of a soil for viticulture. Plant or soil tests using the EUF method can detect nutrient deficiencies and, if necessary, correct them through fertilisation. A comprehensive classification or determination of the soil quality for agricultural use in general or specifically for viticulture is carried out by means of bonitur.
In calcareous soils with pH values above 8, the high calcium content in the soil makes it difficult for other doubly positively charged ions such as nitrogen compounds, magnesium or the trace elements boron, iron, manganese or zinc to be absorbed, so that lime chlorosis or other physiological deficiency symptoms can occur, even with normally sufficient nutrient levels in the soil. 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 basic rule, basic (alkaline) soils with high pH values above 8 (for example, limestone, chalk and marl soils with mostly high levels of calcium and magnesium) produce wines with higher acidity, while acidic soils with low pH values below 6 to 4 (for example, granite, quartz sand) produce wines with lower acidity levels. Trials with increased potassium applications have shown that vines respond 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, other causes (independent of vintage or ripeness-related acidity levels) naturally also contribute to the acidity in wine.
A good vineyard soil should be rather lean, medium to deep, well aerated, water-permeable and not compacted, rich but not too rich, not too humus-rich but rich in mineral components. The best sites are so-called slope sites, because this creates an almost vertical angle of incidence for the sun's rays in late summer, and thus the maximum amount of irradiation can be utilised. The best location on a slope is the wind-calm concave centre (belly, navel, kidney), where the highest temperature sums are reached and the soil is usually well-drained. Soil colour also plays an important role, because dark soils absorb the sun's heat more quickly and extensively, while light soils reflect light, so such soils do not heat up as quickly or as much. The suitability of an area for viticulture is called viticultural 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, predominant in the central and more southern part of the Chianti region
Alluvium/Alluvion (alluvial soil): Alluvial sediment (loose materials) washed up and 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 lasting earth age. Alluvial soils are mostly fine-grained, very fertile soil types that develop in the floodplains and estuaries of rivers. They consist of soil particles that have been washed up and sedimented when the water calms down.
Depending on the sinking velocity of the soil particles carried in the water and the flow velocity of the floodwater, they consist of clayey mud, silt, sand or, in the immediate shore area with high run-off velocities and strong erosion dynamics, gravel and boulders. Despite being predominantly stony and sandy, as in the French Médoc, for example, these soils are very well suited for viticulture. The secret of the sites there are the clay lenses inside the alluvial gravel terraces, deposited during various floods and covered with sand and gravel, which can store water. Such clay layers are literally sought out 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 amphibole 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: Wind-induced phenomena named after the Greek wind god Aeolus. Aeolian transport causes fine material such as loess, silt or clay to be released from the parent material such as unconsolidated rock and transported over greater distances by the wind. Aeolian weathering is the removal of rock by wind-moved grains of sand, fine gravel, etc. with the effect of a sandblast. This creates an aeolian weathering soil.
arcose: The geological term describes a pink to reddish, coarse-grained sandstone with a high proportion of feldspar, which occurs mainly in dry, water-scarce areas. It leads over to the coarser-grained granite rocks.
Floodplain soils: Soils formed from river deposits that 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 soils and parabrown soils. These soils are mostly nutrient-rich, biologically active and fertile.
Basalt: Basic effusive rock (cooled magma) consisting of feldspar, hornblende, olivine and magnetite. It contains a lot of lime and soda and is rich in minerals. The hard, slowly weathering rock forms good soils and produces wines with appealing acidity.
Pumice(Bimsstein, Bimstuff): 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 no different from other lava, but is much lighter due to the trapped air. The colour varies from black and with increasing air content to grey and white. The name Bimstuff 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. It is found throughout the Greek island of Santorini, which was formed from a volcanic explosion. Similar to pumice is obsidian, but it contains much less carbon dioxide. See also under Canava and below under Volcanic rocks.
Blue slate: See below under slate.
Boulbènes: A term commonly used in Bordeaux for a very fine, pebbly soil. It occurs, for example, on the plateau of the Entre-deux-Mers area.
Brown earth: These A-B-C soils develop mainly over low-calcareous but base-rich rocks such as granite, gneiss, greywacke, clay slate and clayey sandstone. Formation occurred under humid climatic conditions from humus-rich topsoil on low-calcareous silicate rock (ranker - see below) with deciduous and mixed forest cover. The brown colouration in the B horizon is caused by iron oxides formed during the chemical weathering of iron-containing silicates. In this process, the acids released by the tree roots strongly contributed to the deep weathering of the B horizon. The lime content, stone content and water balance of brown earths can differ greatly. Depending on its nature, this can be an excellent soil for viticulture.
Parabrown earth differs from brown earth in that clay particles have been shifted from upper to deeper layers. This is a process that occurs during soil acidification. Calcium dissolution causes putty-like lime structures to disappear, so that the released clay particles are washed away with the seepage water into deeper soil layers. Parabrown soils mostly developed from pararendzines. Parabrown and brown soils are the most common soils in humid Europe. Loam and loess parabrown soils are among the most fertile soils.
Breccia: Conglomerate with angular components (see below).
Buntsandstein: Variegated, mostly red sandstone with partly clayey alluvium. The red sandstone was formed from the erosion debris of mountains of the Palaeozoic era. It was deposited in a dry semi-desert climate in a large basin (Germanic Basin) in the middle of today's Europe and later overlaid by sedimentary rocks such as Jurassic limestone or by airborne loess.
Iron: See under Terra Rossa and below under Rotliegendes.
Feldspar: Complex silicate compounds of white and reddish minerals, about 60% of which are involved in 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, pericline, anorthite) and microcline. Weathering produces base-rich clay minerals that 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 marine organisms containing silicic acid (diatoms, radiolarians = marine plankton - see also diatomaceous earth). This soil produces typical wines with a flinty taste, such as the French Pouilly-Fumé.
fluviatile: Worn away or deposited by flowing water - the result is an alluvion or also alluvium soil (alluvial soil); see above.
Flysch: Fossiliferous sandstones as well as marl and clay shales that have formed at the edge of a forming mountain range from the erosion debris. In a narrower sense, these...