Methoxypyrazines in Cabernet Sauvignon and Merlot as affected by leaf removal around bloom (Vitis vinifera L.)

Earlier leaf removal represents a good alternative to widely adopted late leaf removal, which is nowadays loosing many of its advantages due to slightly higher seasonal temperatures and greater UV-radiation within sensitive phases of grape berry maturation. In our experiment, carried out in 2011, we investigated if earlier leaf removals, before flowering and at berry set, both already known to affect phenolic compounds, could in parallel also impact the occurrence of methoxypyrazines in grapes. Those compounds are often causing unwanted ''green'' aromas in red cultivars, especially in 'Cabernet Sauvignon' grapes and wines. Together with 'Cabernet Sauvignon', also 'Merlot' was studied in the same investigation due to its high economic importance for Vipava Valley. Along with basic grape quality and yield parameters, a treatment-related occurrence of two aroma-influential methoxypyrazines (IBMP and IPMP) was monitored during maturation and at harvest time by means of HS-SPME-GC-MS. The results revealed only few minor differences in basic grape quality parameters between the treatments but have indicated some changes in yield parameters in case of pre-flowering approach as compared to control and berry set leaf removal. For both of the methoxypyrazines a different trend between the two cultivars was observed as well as some substantial differences between the treatments were shown. At harvest, the differences in IBMP among treatments were indeed less obvious, however, pre-flowering leaf removal led to a slightly higher content in both cultivars and BS to lower, both as compared to control. In opposite, IPMP was no longer analytically detectable at harvest, thus the small changes triggered earlier in the season became irrelevant. The results suggested that preflowering leaf removal could result in a delay of maturation, which could also explain why methoxypyrazines in case of that very early treatment were decreasing with a slower rate through maturation as compared with berry-set leaf removal and control treatments.