Gran's plots for end point detection in potentiometric titration of wineD. Rudan-Tasic and C. Klofutar
Department of Food Technology, Biotechnical Faculty, University of Ljubljana, SI-1000 Ljubljana, Jamnikarjeva 101, Slovenia
In several samples of Slovenian white wine the concentration of ethanol in extract, pH values, and total acidity were determined, as well as the densities and refractive indices. Total acidity was determined by a classical procedure which is the accepted method of the American Society of Enologists and the AOAC, i.e. the titration of wine with a strong base up to the titration "end point" at pH 8.2. In order to find the true end point, Gran's graphical procedure was employed and some examples of its practical application are illustrated. A Gran's plot converts a logarithmic response to a linear plot and it is shown that in spite of the complex wine matrix, this analytical procedure enables a precise, reproducible and accurate determination of the total acidity of wine.
Key words: Wine / total acidity / potentiometric titration / graphical procedure.
© EDP Sciences, Wiley-VCH 1998