Soil type means different things to different people.
For those selling wine, mentioning the soil type can simply be a marketing technique to romance the product. Back labels on wine bottles are filled with this information. In other fields, sommeliers may flaunt their knowledge by mentioning the soil of a particular region.
What is often missing in the dialogue is the link about why soil is important. Why should the rest of us care?
So, here’s why it matters.
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In general, the #1 most important feature of any soil type is that they provide good drainage.
The number one most important quality about soils, is that vines want good drainage. They really don’t like to get their feet wet.
Therefore, well-drained soils help increase grape quality and more importantly, the resilience of the vine during droughts.
By forcing the roots to grow further and deeper – like waay down into the soil. It’s here where the roots have access to tiny amounts of water during dry spells. Moreover, as there are more root tentacles piercing the subsoil, they pick up more trace elements and nutrients along the way.
To this point, perhaps I should mention that when producers are talking about soil types, they could be talking about the topsoil or the subsoil and they don’t always make this clear. When we are talking about drainage both the topsoil and the subsoil are important.
It’s why WSET wine students and sommelier students are expected to know the soil types of famous wine regions.
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Choosing the right soil type is far more important in Old World vineyards because they are not allowed to irrigate.
‘Old World’ vineyards refers to the wine regions of all of Europe. New World vineyards are those areas developed as a result of European colonization.
Generally, Old World producers are not allowed to irrigate the vines. This is a great advantage for mother earth as European vineyards are planted in places where they get enough rainfall throughout the growing season naturally.
Yet, not only is this a much more sustainable approach to agriculture, it has a fantastic effect on wine grape quality.
Roots are typically multi-branching. The old, woody roots produce lateral roots that can further branch into smaller lateral roots.
In turn, these lateral roots produce many short, fine roots, thereby increasing the surface area of soil exploited.
Water saturated soils do not have the airspace that allows them to breathe.
Why irrigation can possibly be bad for vines...
Therefore, those who rely on irrigation run the risk of misusing the technology.
For example, vines that are frequently irrigated well, don’t need to grow into the subsoil. Instead, they may only grow roots near the surface.
But vines whose roots only grow in the immediate topsoil die quickly when water is no longer available. Furthermore, these vines also tend to be less resilient towards a whole schwack-load of other pests and diseases.
Skilled viticulturalists must know when and how to irrigate their grapevines.
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Hillsides are great for providing good drainage
You may have also heard wine professional talk about hillside vineyards. Indeed, most of the vineyards in the Old World are planted on hills.
In France, it was the monks of the middle ages who recorded wine crop yields and quality over centuries. They were some of the first to figure out that grapes planted on hillsides made the best wine.
Today, we know why.
Did you know?
Through centuries of viticulture, monks were the first to record that hillside vineyards grew the best grapes for making high quality wine.
Hillsides drain rainfall exceptionally well; and vines don’t like to get their feet wet. Instead, the vine roots must stretch deep into the soil where they pick up trace elements and nutrients.
Yet, another reason why hillsides are great for wine grapes is because of the way they face the sun. Grapes grown in cool climates such as Champagne, just barely ripen each year. The south and south east aspects of the hillsides provide a direct route for the suns rays to ripen the grapes.
For some regions, hills provide altitude to improve quality; as for this winery here.
To grow high quality grapes, the soil type generally needs to be poor, infertile soils.
But the second most important thing about soils for vine grape growing, is generally soils should be infertile and lacking in the nutrients.
Planting in infertile soils is an easy way to restrict the vigour or productivity of the grapevine and therefore, produce less grapes.
Yes, I said that. The infertile soils produce less grapes and this is a good thing!
With most agricultural crops, you want fertile soils because you want to produce as many tomatoes or peppers as possible.
However, grapevines are the opposite. Grapevines are essentially weeds so they will grow and grow and grow anywhere. In fact, in many places in Italy and Portugal, grapevines were planted beside trees and just left there. The trees provided a natural, low-maintenance anchor to climb and wrap around.
Because the truth is, if a vine produces too many grapes, the quality of the juice drops.
Instead, grapevines need to fight for their existence in order to produce high quality grapes for wine. This way, the plant focuses all of its energy and sugar production into the few grapes it has to attract birds to eat them.
Therefore, we plant grapevines in poor infertile soils to restrict their natural vigour and produce high quality grapes.
Conversely, grapes grown in the fertile plains such as the alluvial soils left over by riverbeds, produce higher yields of lower quality grapes. This makes absolutely fine inexpensive wines, but it doesn’t make premium wines meant for ageing.
Modern viticultural techniques allow us to control vigour without planting on hillsides
Yet, planting in poor infertile soils is a generalization that more often applies to the vineyards of the Old World and even there it is still a simplified way of presenting a complex topic in one statement.
Many vineyards planted on fertile land can use other techniques for controlling yields and grape quality. Planting at super high densities is one way. Labour-intensive crop thinning is another.
Fertile soil types in the valley plains near rivers produce higher yielding but lower quality grapes
The general idea is that where soils are poor, there are higher quality grapes to be picked. Where soils are fertile, as in the valley plains near rivers, they tend to be higher yielding vines growing many grapes but producing lower quality ones that make easy-drinking, simpler wines.
This isn’t to say that all flat, fertile vineyards make poor wine – noooooo. Viticulturalists have other ways of reducing yields.
It does mean that choosing to plant a vineyard in poor soils will reduce the amount of work you have to do later on to restrict yields.
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Some soil types are warm; some are cool. Soil qualities like these combine with others for optimum grape growing.
If you want to plant a vineyard, you have to be careful to choose grape varieties that will work with the soil. You also need to balance that with the climate of the area.
The soil of Rías Baixes, Spain
For example, one of the reasons why Albariño grows so well in Rías Baixes in the northwest of Spain is due to the granite topsoil and subsoil.
There are 3 reasons for this.
The first, relates to reason #1 above – granite or rocks in general, provide good drainage. See below.
Why does Albariño grow so well in Spain?
Rías Baixes in Spain has a cool and sunny mediterranean climate as the region lays right on the edges of the ocean. So, it also rains a lot.
On average, it rains 1600 mm per year in Rías Baixes, but some estates experience 2000 mm per year. Compare that to Alsace where it rains only 500 mm per year.
Overall, grapevines only need between 300-600 mm of rainfall per year.
The granite soils of Rías Baixes make sure that the vine’s feet aren’t always soaked. To boot, these vineyards are also along the hillsides which helps rid the soils of all that excess rain.
The second reason why granite soils work so well is to due to reason #2. Granite is a poor, infertile soil that helps to keep the yields down.
However, thirdly and perhaps paradoxically, granite is a cool soil that warms very slowly while simultaneously reflects added heat from the sun back on the vines..
With many wines the best flavours are produced with cool temperatures over a long period of time. Slow development of flavours causes better complexity of flavours (think of premium wine regions such as Champagne, Burgundy and Barolo). This is indeed the case with Albarino grapes grown in Rías Baixes, Spain.
Furthermore, cool soils (and temperatures) are able to maintain high levels of acidity in the grapes. And naturally high acidity levels are highly valued by wine professionals. Acidity makes wine mouthwatering; it causes wine to pair with foods excellently and it allows wines to age well.
St Émilion, Bordeaux, France is famous for its cool, limestone soils
Limestone which is a type of clay formed from millions of tiny ancient shells of sea creatures on the seabed is also a cool soil. Limestone is truly unique in that it retains moisture in dry weather, but also offers good drainage in cool weather. It produces high quality grapes especially in cool climates.
As a perfect example, the best estates in St. Émilion in Bordeaux have cool, limestone and clay soils that maintain acidity in Merlot grapes.
Because in many wine regions that grow Merlot, their wines are plush with dark plum fruits and chocolate. They are smooth and velvety, but they cannot age in your cellar for long.
Only in St. Émilion are the soils cool enough to get the fruit ripeness in the grapes AND retain high acidity for long ageability.
On the flip side of the coin, warm soils are also important to certain regions because they can help ripen grapes in marginal climates.
For example, the slate rocks of the Mosel Valley help to reflect heat back onto the vines to increase ripening in the marginal climate of northern Germany.
Sandy soils are warm soils.
In fact, by knowing the soil types of where grapes were grown, you can more accurately predict how a wine will taste.
But it's not just the quality of the grapes and wine structure that are affected by soil types. Changes in the soil affect the flavour of the wine too.
If you speak with the producers in Burgundy, France, they will ALWAYS talk about the soil and the flavour of the wine in the same sentence.
That’s because small changes in the soil type change the way the wine tastes. Even when it is the same grape variety, same winemaking, same vintage, and the same producer involved.
It’s so important, entire books are dedicated to mapping the tiny differences in soil throughout Burgundy.
Here is a graph of the changes in soil type on the Côte (hillside) in Burgundy.
More to this point, is this video of Edouard Labruyère, the owner at Maison Jacques Prieur in Burgundy, France. Listen to how he explains the flavour difference between his wines – all from vineyards within the same Beaune village appellation in Burgundy. The changes all have to do with the soils the grapes were grown in.
The same grape variety grown in warm sandy soils will produce a different wine if grown in clay-based soils like limestone.
In warmer climates, sandy soils generally produce wines that are softer (lower in tannin), paler in colour, and higher in elegant aromatics.
Conversely, wines whose grapes are grown in clay-limestone soils, are more tannic, deeper in colour and have bolder flavours.
Chianti wines made with Sangiovese illustrate how soil affects flavour
Galestro, a schistous, marl-like sand with a touch of clay produces wines that are more robustly fruit-driven. These soils are generally found in the higher elevations of Chianti.
Alternatively, albarese, a white clay that’s generally found in the lower elevations of Chianti, produce wines that are more savoury and mineral.
Let’s bring back the example of the Merlot-based wines grown on the limestone-clay soils of St Émilion in Bordeaux, France. Now, you can perhaps understand why the wines here are structured (tannic), deeply coloured and have high intensity of flavours.
For most people drinking wines, soil types shouldn’t really matter. However, if you really love wines from a particular region, it may be worthwhile for you to dive deep into the soils of the area and how they affect the flavour and quality of the wine.
Because I’m sure wine professionals will continue to romance soils types with the wines they sell. I just wish more of them would share why those soils are important to the wine’s quality and taste.
Because some soils provide excellent drainage to ward off excess rainfall. Cool soils help grapes maintain their mouthwatering acidity, a necessary element for ageing wines. Conversely, warm soils can help ripen grapes in marginal climates. Finally, and perhaps most importantly diverse soil types change the flavours in the wine.