A vineyard’s ‘below-the-ground’ terroir is an important element in understanding contributors to a wine’s character. But why is it so important? What are the best terroirs?

A vineyard’s ‘below-the-ground’ terroir is an important element in understanding contributors to a wine’s character. After all, vine roots can extend up to 3 metres below the soil surface. So the composition and intrinsic nature of the vineyard soils, such as fertility, drainage and ability to retain heat play major roles, but so do the microbes and fungi that exist within it.

There are many different types of soil, rock and mineral deposits in vineyards around the world. Yet most vineyard soils are one of five or six different types that affect the flavours of wine through their impact on the supply of water to the vine.

The best terroirs are where soils are free draining, with the water tables beneath being high enough to ensure a regular supply of water to vine roots but which then recede when the grapes change colour at veraison, so that the vine plant growth stops and the vine concentrates its energies on ripening the grapes.

Typically vines planted on slopes will produce better quality wines. The bigger the slope, the better. This is because the soil on slopes is shallower. Therefore it drains well and does not hold a lot of nutrients. This makes the vine struggle and produce smaller berries. This is particularly important for red wines where there is a reduction in the surface area to volume ratio which results in more colour, flavour and tannin from the skins to be absorbed into a naturally smaller volume of wine. This makes wine that is richer and more fully bodied, allowing it to age for longer.

It appears that the chemical composition of the soil with its nutrients, is only important when there is excess nitrogen (leading to excess vine vigour) or when there is a serious deficiency. Interestingly, nutrition can produce specific growth patterns of vines, causing specific canopy architectures and patterns of grape ripening. A vine’s performance seems to create a specific microclimate in the bunch zone, and in this way can determine the character of the wine.

While there appears to be an absence of scientific proof that associates the taste of ‘minerality’ to actual minerals in a wine, it is accepted that something does happen. It’s seems that soils act on the water as it passes through to the vine’s roots. For example, vineyards grown on granite soils are sometimes described as graphite-like, gravely or like damp concrete. Yet granite is best known for its heat reduction action and reducing acidity in high acid grapes.

The microorganisms in soils and particular vineyards are also important. Besides health benefits, it is believed that microbes tell us a lot more about wine than we ever thought.

We can analyse microbes in vineyard sites and in wines to connect those wines to sites. The unique biogeographic fingerprint based on the types and amounts of fungi and bacteria present in grape must has been proven. It means that every wine has a unique biological indicator of where it’s from! But it’s not clear how these microbial differences link to how a wine tastes.

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