Influence des teneurs en acide malique des moûts sur le dosage de l'acide tartrique par analyse en flux continu par colorimétrie avec le métavanadate

Les auteurs ont constaté que la méthode en flux continu, qu'ils utilisent pour doser l'acide tartrique dans les moûts et les vins basée sur la réaction colorée avec le métavanadate et dérivée de la méthode rapide de BLOUIN-VIDAL ne donne pas satisfaction, Ils constatent des écarts inférieurs à 20 p. 100 par rapport à la méthode de REBELEIN qui repose sur le même principe. Ces écarts sont dûs à l'interférence des autres acides organiques du moût et du vin, notamment l'acide malique, interférence corrigée dans la méthode de REBELEIN. La comparaison des trois méthodes précitées les conduit à proposer pour la méthode en flux continu l'application d'un facteur correctif pour tenir compte de la présence de l'acide malique en concentration importante dans les moûts du Val de Loire. +++ The authors noted that the continuous flow method based on the colorimetric method with metavanadate, derived from the method of BLOUIN-VIDAL, for the tartaric acid determination was not satisfactory. They noted variations, by 20 p. 100 lower, compared with the method of REBELEIN based on the same principe. These variations are due to the interference with the other organic acids of musts and wines, especially malic acid, which is limited in the method of REBELEIN. The comparison of the three methods induce the authors to propose for the continous flow method the utilisation of a factor to correct for the presence of malic acid at large concentration in the musts of Val de Loire

Comprehensive chemical study of the acidification of musts in Sherry area with calcium sulphate and tartaric acid

Calcium sulphate addition has traditionally been used in Sherry winemaking to reduce the necessary dose of tartaric acid. It is not easy to predict the final pH of a mixed tartaric acid and calcium sulphate addition and to determine the necessary doses to reach the final pH required by the winemaker because there are several interrelated chemical equilibra implied (tartaric acid dissociation, calcium tartrate and potassium bitartrate precipitation etc.). To predict the effect on pH, several chemical modeling approaches have been described in the literature. It is noteworthy to mention the simplified model where the acidity of wine is considered to be due to a monoprotic acid. In this work the prediction of pH at industrial scale was confirmed and its practical application was facilitated by linear regression lines prepared with pilot scale data. Additionally, sensory analysis of wines acidified with calcium sulphate and tartaric acid alone and mixed indicates that there are great differences among them in taste and that mixed acidification is the preferred by the tasters. That confirms the good comprehension of the chemical equilibria involved in this practice and supply very useful information for its final approval in OIV