A wine lover regularly meets these terms: limestone, clay, gravel, sandy soils... As you know it, soils have a huge influence on the style of wine that is produced.
Yet, I found it quite difficult to understand how all the terms were categorised. I therefore created this super simple infographic to provide an introduction to soils' types. I hope this will help!
Some more details below.
Igneous rocks: Forming from the cooling of magma
Metamorphic rocks: Forming from the slow metamorphosis of igneous and sedimentary rocks
Sedimentary rocks: Forming from the solidification of sediments (organic or inorganic)
Soils' factors influencing winegrowing
The water-holding capacity of soils strongly impacts winegrowing. Stones and sand are coarse-grained, they are porous to water and nutrients and it is easy for vine roots to grow deep in the soil in these textures. These soils dry fast and keep the warmth. In a dry environment, vines can however suffer from water stress as the water escapes easily. At the opposite, silt and clay are defined as finely grained, leading to soils with a spongy texture that holds water and nutrients and remains wetter and colder. Roots don't grow deeply in these types of soils, it is difficult and they find all the resources they need at the surface. In a wet environment, these soils can easily get waterlogged. Too much water in the soils leads to too much fertility of the plant and too much water in the grapes at ripening (dilution of aromas, acidity, sugar). Worst, vines can even die because there is no more space for oxygen in the soil, which is needed by the roots for the vine to survive.
The colour of the soils has also a leading role in winegrowing. Light coloured soils reflect sunlight and warmth, helping the vine to ripen. This can be especially helpful in cool climates. Dark coloured soils store warmth during the day and release it to the vine at night. It can be useful in cool climates where there is a high diurnal range (the high difference between day and night temperatures), where night temperatures drop a lot.
It would be wrong to associate each texture of soil to a style of wine. There are too many other factors to take into account. The most important is to plant the right variety in the right soil-climate combination. And there are many possible combinations. Here are some famous examples:
In Médoc (Bordeaux) rainy climate, cabernet sauvignon is a late-ripening variety that grows well in the gravelly soils. Water is well-drained and soils stay warm, allowing the variety to ripen fully. This variety would not do as good in clay as soils would be too wet and cold.
Right in front, on the Right bank of Bordeaux, merlot needs the cool and wet clay soils. It ripens early and would become too jammy in warm and dry soils.
In Mosel (Germany) cold climate, riesling is a mid to late-ripening variety that can grow thanks to black slate soils: releasing warmth during the night to accelerate ripening.
Thanks for reading :)