Changes in Grape Firmness During Maturation

Puncture force with skin on, puncture force with skin off, deformability, and ˚Brix were measured on six cultivars of grapes grown in northeastern USA as they matured over a six week period. Deformability increased steadily throughout the maturation period. ˚Brix increased rapidly following veraison and then continued to increase at a slow rate. Both puncture forces decreased rapidly at veraison and then continued to decrease at a slower rate. The puncture force with skin on was always much higher than puncture force with skin off. All the physical properties correlated well with each other and with ˚Brix (with a few exceptions). The puncture test with skin on usually gave the highest correlation with ˚Brix. It could probably be used as an alternative test to ˚Brix or as a confirmatory test to supplement the ˚Brix reading.