Indirect effect of glyphosate on wine fermentation studied by microcalorimetry

The use of herbicide such as glyphosate is a common practice in viticulture to limit nutrients and water competition between vine/weed plants. However, the impact of such herbicide on the resulting grapes juice quality and, later, on wine fermentation has not yet been proven. In this work, grapes of Vitis vinifera L. cv Gewürztraminer harvested from plants subjected to the weed control with glyphosate were analysed for their fermenting capacity by isothermal microcalorimetry after inoculation with Saccharomyces cerevisae. The resulting heat flow traces were fitted by two additive Gompertz functions and used to describe the yeast growth rate. The comparison of the fitting parameters showed that glyphosate decreased the heat generated by yeast growth. This effect was consistent with a change in the amino acids and sugars contents in grapes. However, the results also show that the impact of the herbicide on yeast fermentation can be partly overcome with an additional N fertilization (i.e. urea) in the vine. Microcalorimetry has revealed for the first time these effects on the fermenting process of grapes.