Synthesis of Tartaric and Malic Acids by Grape Vines

¹ Station Agronomique et Oenologique de Bordeaux

In the general plan of a study of the composition of the leaves of the vine in the course of their vegetative cycle, we have followed the evolution of tartaric and malic acids. While tartaric acid undergoes rapid fluctuations around a constant average value, the malic acid continuously increases. The leaves of the vine have three times as much malic acid in October as at the beginning of May. Comparison of the composition of the leaf and the fruit does not permit establishing a simple relation between these two plant tissues. The leaf, which is much more rich in mineral substances maintains its acids and continues to accumulate them while the fruit is deacidified beginning with the opening period. It would not be exact to stay that the acids of the grape are oxidized in the leaf. Finally, comparison of the composition of the fruit of recent vintages shows that at the same stage of its development the fruit has for a fixed amount of total acidity, a varying balance, according to the year, between tartaric and malic acids. One distinguishes seasons when the tartaric acid is more elevated than the malic acid and the reverse. This Character is met with for different varieties and in various vineyards. Finally, the tartaric acid of the fruit contributes to the same extent as malic acid in fixing the final acidity of the frut.