Assessment of grape skin hardness by a puncture test

BACKGROUND: The release of grape components during wine making might be related to the mechanical properties of the skin, in particular its hardness. Samples from three varieties collected during the 2005 vintage season in Piedmont, Italy, were tested for their skin hardness using a texture analyser. The goal was to understand the statistical interactions between three factors – variety, cluster position and puncture point – and their influence on the grape skin hardness. A discussion on the relationship between the size of the sample used and the confidence level is also provided. RESULTS: Results of the ANOVA test showed that there is an interaction between the variety and the puncture point when measuring the skin hardness with the break energy. The position of the berry on the cluster does not affect the berry skin break energy. We also show that a sample size depend on the variety tested. CONCLUSION: The break energy is more useful in understanding the effect of the three factors on the skin hardness. Other factors that might affect the puncture test applied to grapes need to be studied in the future and the usefulness of the test in winemaking will need to be further developed.