Changes in Berry Firmness of Various Grape Cultivars on Vines Measured by Nondestructive Method before and after Veraison

Time-course changes in the elasticity index (EI) of 8 cultivars and 1 selection of grape berries on vines were investigated with a nondestructive acoustic method. A portable device was constructed for the measurement of grape firmness. The EI was determined by the formula EI = f22 · d2, where f2 and d were the second resonant frequency and the diameter of the sample respectively. In all cultivars, the date of veraison was judged by touch and the EI largely decreased around veraison. These changes were classified into two types; one decreased before veraison and the other after veraison. The EI was compared with the firmness measured by two penetration methods. Relationships between the EI and firmness measured by the penetration methods were classified into three types of regression curves; a linear relation which detected similar berry firmness with both the nondestructive method and the penetration methods; logarithmic, in which the nondestructive method was more sensitive when berries were hard; and exponential, in which the nondestructive method waas more sensitive when berries were soft. We concluded that these differences were caused by differences in the spatial softening process.