Sugars in grapes: Intra- and inter-cluster variability

Department of Agricultural, Food and Environmental Sciences, University of Perugia, Italy

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Abstract

The study, conducted in 2023 on Chardonnay, Pinot Noir, Trebbiano Toscano, and Sangiovese, investigated sugar concentration variability within and between clusters during ripening. The objectives were: (i) to assess intra-cluster sugar variability among individual berries, including the effect of berry exposure, and (ii) to compare the technological ripening of basal and upper clusters on the same shoot to support thinning decisions.Within each variety, marked differences were observed between the richest and poorest berries, ranging from 12 °Brix in Sangiovese to 16 °Brix in Trebbiano Toscano. No significant differences emerged between the external and internal portions of clusters. Similarly, no significant inter-cluster differences were found between basal and upper clusters in terms of sugar content, organic acids, or pH.As ripening progressed, sugar accumulation tended toward greater homogeneity, while very high sugar levels (>25 °Brix) were mainly associated with berry dehydration. Trebbiano Toscano and Sangiovese showed heavier basal clusters compared to upper ones, suggesting that thinning should preferentially remove upper clusters to avoid yield and sugar losses. Conversely, to limit sugar accumulation and potential alcohol content, removal of basal clusters is recommended.