Quantification of acetic acid, malic acid, sorbic acid, fumaric acid and shikimic acid according to the PULCON/NMR method [15]. In all cases, an external reference of each metabolite, with known concentration, has been used for calibration. External standards were prepared in concentrations close to the OIV reference mean value (dotted red line) as follows: [acetic acid] = 650 mg/L; [malic acid] = 1436 mg/L; [sorbic acid] = 152 mg/L; [fumaric acid] = 49 mg/L; [shikimic acid] = 51 mg/L.