Berry size and maturity affect phenolic extraction into Pinot noir wines

Abstract

Berry skin and seeds differ in their phenolic content, structure and accumulation dynamics during maturation. Therefore a change in berry size or maturity level may affect their contribution to wine composition. Grapes of Pinot noir (clone Gm1-1) grafted on SO4 rootstock from an established vineyard at Geisenheim (Germany) were segregated into different size groups at harvest over three seasons to investigate phenolic extraction into wine using a micro-scale fermentation technique. The segregation showed that wine tannin concentration increased whereas anthocyanin concentration decreased with increasing berry size but groups differed in sugar concentration. When sorting berries according to their total soluble solids (density), wine tannin concentration decreased with increasing Brix; however berry size decreased concomitantly, making a final conclusion difficult. In order to test the effects of size and maturity independently, berries were first segregated into diameter size groups and then each group into different density subgroups. A shift towards higher sugar concentration with decreasing berry size was observed. When considering one population of similar berry size, a higher anthocyanin extraction into wine was observed under increasing Brix, corresponding to an increase in alcohol content of the wines. For the same density subgroup, wines produced from smaller sized berries showed higher anthocyanin extraction compared to wines from larger sized berries probably as a result of the greater skin to juice ratio during the fermentation process. A lower tannin extraction into wine was observed with increasing Brix. For the same Brix population, wines produced from smaller sized berries showed lower tannin concentration compared to wines from bigger sized berries. Seed number per berry and seed tannin concentration increased with berry size, which in fact may explain the higher tannin extraction with increasing berry size.