Abstract: Berry size is generally considered to be an important quality indicator of grapes. In this study, ‘Merlot’ and ‘Cabernet Gernischt’ grapes were divided into large, medium and small sizes (diameter): > 14 mm (L), 12–14 mm (M), and < 12 mm (S) for ‘Merlot’; > 15 mm (L), 14–15 mm (M), and < 14 mm (S) for ‘Cabernet Gernischt’. The contents of soluble solids, titratable acids, anthocyanin monomer and monomeric phenols in grapes of different berry sizes were determined over two consecutive years. The results showed that the percentage of medium berries was higher for both varieties and both years. In 2014, soluble solids content (SSC) decreased as berry size increased for both varieties, while in 2015 middle berries had a higher level of SSC. For both years, seed/berry ratio and the number of seeds in individual berries decreased with decreasing berry size, and phenolic contents were higher in small and medium berries for ‘Merlot’ and large and medium berries for ‘Cabernet Gernischt’. The highest total monomeric anthocyanin (TMA) content was found in medium berries for ‘Merlot’, while TMA levels in ‘Cabernet Gernischt’ grapes varied greatly with years. For ‘Merlot’ grapes, total monomeric phenol and flavonol contents were higher in medium berries, while for ‘Cabernet Sauvignon’ higher levels were found in large berries. In conclusion, phenolic contents were higher in medium berries for ‘Merlot’, while large berries had higher phenolic contents for ‘Cabernet Gernischt’.

Key words: ‘Merlot’ grape, ‘Cabernet Gernischt’grape , berry size, grape quality