Lydia and Claude Bourguignon, 2 leading French Soil Microbiologists

What is the Terroir?

Lydia and Claude Bourguignon have founded in 1990 the Laboratory of Soil Microbiology Analysis (LAMS) and profiled since more than 8,000 soils all over the world. We are sharing some of their findings here, to explain in a very succinct manner, how the soil life works and how this influence the Terroir and eventually, the taste of wine.

Soil Horizon

To sustain life on this planet we need water, air and soil. While water and air can be polluted, their molecules atomic bond is very resilient. Soil on the contrary, is an aggregate of minerals and organic matter, the clay humus complex, with weak electric bond, easily destroyed and wash over to the sea.

A quick glance at the soil formation mechanism shows the importance of preserving and encouraging soil micro-organisms.

Epigeal fauna on the surface digest the lignin from dead leaves, wood, and animal wastes, turning them into organic matter which is then further decomposed into humus by mycorrhizae.

In the sub soil, another kind of endogenous fauna will aerate the ground and provide oxygen to fungi and bacteria, allowing the vine roots to go down until they reach the bedrock. There, roots will produce sugars and acids to attract microbes and turn the rock into clay.

Meanwhile, earth worms are traveling up and down, mixing clay (a negative charge) in the subsoil with humus (a negative charge) in the topsoil via their digestive tract, rich in calcium (2 positive charges), creating soil, a clay-humic complex which they excrete at the surface.

Since the 1950s, as farmers started to use agrochemicals, French soils have gone from containing 2,000kg of earthworms per hectare to under 100kg.

Plant Nutrition

A plant will make 94% of its dry matter out of thin air.

Carbon, oxygen and hydrogen produce sugars during the photosynthesis. Sugar will make alcohol when the grapes juice is fermented, but it does not have much flavors.

The wine aromatic complexity comes from the soil, which accounts for only 6% of the plant dry matter but provide 8 times more elements. Most of which are enzymes cofactors necessary to synthesize the aromas compound that we enjoy in a glass of wine.

One can use X amount of fertilizers to produce X amount of grapes but without a healthy soil, the wine will lack complexity. It will be mostly water, alcohol, with a bit of colour and flavour.

The plants have developed an extremely subtle mechanism to be able to feed themselves in a poor environment.

If the soil is in good condition, the clay-humic complex has a cation exchange capacity (CEC), where nutrients with positive charges (magnesium, potassium, calcium, sodium…) are maintained in equilibrium with the soil water by the osmotic law.

To fight against this osmotic pressure and be able to absorb the nutrients contained in the soil, the plant will send part of the elaborated sap (rich in sugars created via photosynthesis) from the leaves to her roots to produce energy (ATP to ADP).

This energy create an electric charge on the roots that will attract soil elements with positive charges to stick on its root, and wait until the microbes turn these elements into nutrients with negative charges (nitrates, sulphates, chelates…), minerals which will go through the roots active membranes and be pumped with the raw sap to the leaves.

The quality of the grapes produced will depend on the plant's ability to absorb these subtle trace elements in the soil.

Top soil vs Sub Soil

We can see in this analysis of different profiles across the 7 hectares of Clos de Tart in Burgundy that the topsoils coloration and composition are quite homogeneous but the subsoils are completely different.

The difference of assimilable elements (CEC) for the plants are located in depth. Some zones are better suited for white rather than red wine, and will produce grapes that will go either in the top wine or second wine.

Soil comparison Macronutrients

Domaine Leflaive's parcels of Clavoillon and Batard-Montrachet have been divided into 2 different culture, organic and biodynamic.

When you look at macronutrients, there is not much difference in the topsoil, but there is statistical evidence of higher assimilable content in the subsoil with biodynamic farming methods (10x more Phosphorus, 2x more Potassium, 4x time more Sulfur...).

Soil Comparison Micronutrients

Now, we look at the micronutrients content on the same 2 parcels, similarly, there is not much difference observed between organic and biodynamic farming in the topsoil but there is more microbiological activity in the subsoil with biodynamic methods, hence more elements assimilable by plants.

All these trace elements will help the plant to perform the synthesis of aromatic compounds, as enzymatic cofactors. The more a soil is teeming with life, the more complex the soil will be, and the more aromas and complexity the wine will have.

Unfortunately, since 1990, the LAMS has measured a sharp decline of soil microbiological life around the world. We can unfortunately bypass the complexity of the soil by adding oenological products like yeasts that taste like raspberry or banana for example, but we can no longer speak of terroir.

So does organic wine taste better?

Yes, according to experts ratings. A study published in the Journal of Wine Economics in 2016 analyzed the ratings of 74,000 wines produced in California between 1998 and 2009 from three leading publications (Wine Advocate, Wine Enthusiast and Wine Spectator) indicate that eco-certification is associated with a statistically significant increase in wine quality rating by 4.1 points on average.

As a conclusion, we strongly encourage you to demand for organic wine, wherever you go. We can feed the entire planet sustainably and put carbon back into the soil. It is better for the environment, better for the people living on and around the farms and it is definitely more enjoyable to drink. The key to produce quality crops is biodiversity not agro-chemicals.