Within-vineyard spatial variation impacts methoxypyrazine accumulation in the rachis of Cabernet-Sauvignon

Abstract

AIM: To investigate the impact of spatial variation in vine vigour on the accumulation of methoxypyrazines in the rachis of Cabernet-Sauvignon. Cabernet-Sauvignon rachis has been shown to contain significantly higher concentrations of 3-isobutyl-2-methoxypyrazine (IBMP) than that found in berry material. IBMP is readily extracted from rachis during fermentation and can impact the flavour profile of the produced wine1.

METHODS: Cabernet-Sauvignon vines (n = 105) grown on common rootstocks in Coonawarra, South Australia, were georeferenced and 6 bunches were harvested from each vine at maturity in 2020. Berries were removed and the rachis was analysed for IBMP by GC-MS/MS. Pruning weights were recorded as an indicative measure of vegetative growth over the past season. Visualisation and analysis of map layers was achieved through linear regression models and k-means clustering with the Precision Agriculture Tools plugin2 for QGIS software suite3.

RESULTS: Georeferenced maps of vine vigour and IBMP concentration in rachis showed similar spatial variance and a clear relationship between the two variables was evident across the vineyard. k-Means clustering revealed 3 distinct zones identified as high, medium, or low in both IBMP levels and vine vigour. Although rootstock influenced vine vigour, rootstock effects were much less than the variation in vine vigour caused by inherent vineyard variability, most likely variation in soil depth4. Linear regression between vine vigour and IBMP in rachis showed a statistically significant relationship (p < 0.001) and highlighted increases in vine vigour, which increased canopy size and decreased porosity, resulted in an increase of IBMP in rachis.

CONCLUSIONS

Vine vigour significantly correlates with IBMP in Cabernet-Sauvignon rachis. Their similar patterns of within-vineyard variation provide opportunities for grape growers to implement targeted management of vineyards in a zonal fashion.