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There is scant literature on the assessment and validation of methods for monitoring grape texture during ripening. There is a distinct lack of information from published work on the correct procedures to set up texture method. If the measurement of grape texture is to be used for assessing ripeness and further extended to the assessment of polyphenol extractability potential, the relationship between physicochemical parameters and sensory descriptors should be evaluated as a matter of importance. In this work, the physical properties of grape texture during ripening were addressed by an assessment of the relationship between the methods of double compression and puncture tests. The second part of the study reported here applied the methods developed in the first year to grapes sampled in the following year. The results showed that the mechanical texture measurements were able to discriminate grapes coming from different parcels and correlations were found between texture parameters and sensory descriptors. PRACTICAL APPLICATIONSThis paper defines the measurement conditions for monitoring grape texture, particularly during ripening. These established methodologies provide enologists with the tools to monitor the progress of grape maturity, and these mechanical methods compare favorably with the expensive and timeconsuming classical methods. These established methodologies could also be 1 Corresponding Journal of Texture Studies 40 (2009) 511-535. © 2009 used to highlight important information on grape evolution during ripening and help to provide better insight on the choice of the preferred/ideal harvest date. These tools, providing enologists with data on the evolution of fruit texture, could be used to help select more suitable winemaking processes as well, as the extractability of compounds present in the fruit is probably linked to its texture.

Crop nitrogen status is a major issue for crop yield and quality. It is usually assessed by destructive leaf or petiole tissue analysis. A quantitative nondestructive optical estimation of N sufficiency would be a great leap forward toward precision crop management. We therefore calibrated three optical indices against leaf nitrogen content: chlorophyll (Chl), epidermal flavonols, and the nitrogen balance index (NBI), which is the ratio of the former two indices. NBI was the best estimator of leaf N content measured by the Dumas or Kjeldahl method with a root-mean-square error smaller than 2 mg of N g(-1) dry weight, followed by Chl (3 mg g(-1)) and flavonols (4 mg g(-1)). This allowed us to propose the threshold values for the Dualex optical indices that characterize nitrogen supply to grapevines: the first is the threshold below which N supply to the vine can be considered deficient, and the second is the threshold above which N supply is excessive. For a putative optimal N content of 30 mg g(-1) < x < 40 mg g(-1), these thresholds are 30 μg cm(-2) < x < 40 μg cm(-2) for Chl and 11 < x < 18 for NBI at flowering. At bunch closure, for N thresholds of 22 < x < 32, Chl is 29 < x < 37 and NBI is 8 < x < 11, in respective units. These values should be verified and refined in the future for various growth regions and cultivars using the specified protocol. The sample size should be 36-60 leaves from a fixed node position, preferably node no. 5 from the tip of the shoot. An alternative to the use of the NBI would be to discard leaves that are not light exposed by checking their flavonol content and to deduce the N sufficiency directly from the Chl values.

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