Varietal differences in the sugar content of red grapes at the onset of anthocyanin synthesis

The aim of this work was to study the sugar content of grapes at the onset of anthocyanin synthesis, in eighteen red grape varieties for three years. Sugar content at start of anthocyanin synthesis was measured during three years in eighteen red grape varieties under the same climatic conditions within DOCa Rioja. There were significant differences between varieties with respect to sugar content of grapes at the onset of anthocyanin synthesis. Varieties with the lowest sugar content at the beginning of anthocyanin synthesis, every year, were 'Alicante Bouschet', 'Moristel' and 'Trepat' (between 7 and 9° Brix) and varieties with the highest sugar content were 'Trousseau' and 'Grenache' (between 10 and 14° Brix). The rest of varieties showed, every year, a sugar content ranging between 9 and 10° Brix. The difference between the variety with higher sugar content at the start of anthocyanin synthesis ('Troussseau') and the variety with lower sugar content ('Alicante Bouschet') was about 6° Brix for the three years. On the other hand, there was no relationship between the sugar content at the onset of anthocyanin synthesis and the date on which this anthocyanin synthesis occurred. The sugar content at the start of anthocyanin synthesis for each variety in different years is much more stable than the dates that this synthesis occurs. Therefore, in the study of varieties regarding their cycle, it would be very interesting to take into account not only the phenology or the date on which the veraison occurs but also the berry sugar content at the onset of anthocyanins synthesis.