In order to evaluate the sensitivity of fruit cracking, different laboratory tests were performed in grape berries of the processing varieties Concord, Isabel and BRS Rubea. To determine the cracking index, ripe berries were dipped in distilled water and evaluated every hour during a period of ten hours. Mechanical tests were performed using a texturometer. In compression tests, at the cracking time, pressing pressure, strain energy, maximum force of compression and compression strain were evaluated. With a smaller diameter probe, berries were drilled to the breakup of the skin resulting in maximum force of drilling and drilling strain. In stress relaxation tests the degree of solidity and initial stress decay rate were evaluated. The correlations between the cracking index and mechanical testing were evaluated too. Both the cracking index and mechanical testing pointed to the BRS Rúbea as the most resistant to cracking and the Concord cultivar as the most susceptible. Isabel presented intermediate resistance. The cracking index showed strong correlation with the parameters evaluated in the mechanical tests and has good potential for assessing the sensitivity to cracking of different grape cultivars.
grape; cracking index; compression; drilling; relaxation
