Assessment of the optimal number of observations in the study of vineyard soil (Rigosol)

Since 1996, we study the soil in viticulture, specially in the South of France. In the field, we delimit soil units and observe soil profiles and take samples to analyse its physical, mineral, organic and microbial mass composition

The vineyard of Bergerac, a guaranteed vintage, is situated in the mid-Lot valley, which has siliceous terraced rows on its hillsides, and on its bordering plateaux, composed of limestone and clay of the tertiary geological eras.

The viticultural regions of the world have the advantage of a remarkable diversity of landscapes which are the reflection of the winegrowers’ capacity to adapt to the different geomorphological and climatic specificities of the terroirs, more generally speaking, this aesthetic and heritage aspect of the terroir is also part and parcel of the notion of sustainable viticulture.

Climate change and harvest date decisions have led to the evolution of must quality over the last decades. Increases in must sugar concentrations are among the most obvious consequences, quantitatively. Saccharomyces cerevisiae is a robust and acid tolerant organism. These properties, its sugar to ethanol conversion rate and ethanol tolerance make it the ideal production organism for wine fermentations. Unfortunately, high sugar concentrations may affect S. cerevisiae and lead to growth inhibition or yeast lysis, and cause sluggish or stuck fermentations. Even sublethal conditions cause a hyperosmotic stress response in S. cerevisiae which leads to increased formation of fermentation by-products, including acetic acid, which may exceed legal limits in some wines.

Malolactic fermentation (MLF) is a secondary wine fermentation conducted by lactic acid bacteria (LAB). This fermentation is important in winemaking as it deacidifies the wine, converting L-malic acid into L-lactic acid and carbon dioxide, and it contributes to microbial stability. Wine pH is highly selective, and at pH below 3.5 generally only strains of O. oeni can survive and express malolactic activity, while under more favorable growth conditions above pH 3.5, species of Lactobacillus and Pediococcus may conduct the MLF. Among the LAB species Lactiplantibacillus plantarum strains have shown most interesting results under hot climate conditions, not only for their capacity to induce MLF, but also for their homo-fermentative properties towards hexose sugars, which makes them suitable for induction of MLF in high pH and high alcohol wines, when inoculated at the beginning of alcoholic fermentation.