In order to investigate the extent of respiro-fermentative metabolism of the different yeast strains included in this study (Table 1), the RQ was determined under fully aerobic conditions, in the presence of about 200 g/L of sugar and pH 3.5, as described in the Materials and methods section. A simple stoichiometric calculation (Fig. S1), just taking energy metabolism into account, indicates that the percentage of sugar metabolised by respiration would be equivalent to 100/(3RQ-2).