South African Table Grape Industry (SATI)

A grape bunch contains berries and a rachis – two dissimilar tissues susceptible to different postharvest issues. A waxy coating protects berries from water loss, whereas the unprotected rachis is vulnerable to drying and browning. The rachis can also freeze below minus 1.0 °C, whereas berries freeze at minus 2.0–minus 3.0 °C. Grapes are non-climacteric fruit. Berries have a low respiration rate and, therefore, a low sensitivity to physiological disorders but a high sensitivity to senescence. Pre-optimally harvested grapes won’t ripen, but overmature grapes are more likely to suffer postharvest decay and internal browning. “Soluble solids are a measure of acceptability to the consumer – very high values could occur at a senescent stage of the tissue,” says Dr Juan Pablo Zoffoli, a postharvest physiologist in the Faculty of Agronomy and Natural Systems of the Pontifical Catholic University of Chile.