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GRAPEGROWING Ripening Disorders Not all shrivels are created equal; how to recognize and react By Bhaskar Bondada T he ripening process for grape berries involves a coordinated series of changes in color, texture, volatile expression and (most importantly) the accumulation of sugars. Provided the berries follow these highly coordinated events of ripening, a soft and edible fruit with desirable organoleptic qualities will develop as the ultimate end product, one that is suitable for consumption and winemaking. Conversely, perturbations in the cascade of events result in various ripening disorders, the most striking feature of which is the shriveling of the berries. Each shrivel form develops with distinct characteristics, resulting in distinguishable features in composition and appearance of the berry. These ripening disorders are considered physiological in nature, resulting from altered metabolism and the disruption of normal ripening processes, eventually compromising fruit quality attributes and yield; what precisely causes them are not known. The images accompanying this story illustrate chief distinguishable features of each shrivel form that can help growers separate healthy clusters from afflicted ones at harvest to maintain fruit quality. Sunburn Vineyard conditions that favor sunburn include open canopies induced by deficit irrigation, leaf removal and reduced use of nitrogenous fertilizer. Sunburn is mostly observed in clusters that are exposed to direct solar radiation on the west aspect of the canopy. Both red and white varieties succumb to sunburn, wherein one hemisphere remains constantly exposed to the sun (except on cloudy days), while the other hemisphere develops in shade (see photo on this page) Most of the injury occurs on the exposed hemisphere and is manifested as loss of crystalline structure of the bloom, resulting in a shiny surface. As opposed to red varieties, sunburn in white grape varieties causes brown lesions in addition to the polished exterior surface. 96 W in es & V i ne s JANUARY 20 13 Sunburn Sunburn affects the hemisphere constantly exposed to sun, creating a shiny surface. The overexposed surfaces show reduced color development (pink color), which is very pronounced if sunburn occurs during early phases of ripening, when berries of red varieties transition into veraison. Sunburn during pre-veraison in both varieties causes dehydration followed by the collapse of the whole berry, which eventually turns brown in color. Severe sunburn in post-veraison berries leads to complete desiccation and raisining in both red and white varieties. The feature that makes sunburn distinct from other ripening disorders is the polished appearance of the skin. Despite the overexposure to radiation and temperature, sunburned berries are suitable for making certain styles of wine. Management: Since sunburn is primarily associated with poor canopy management practices, resolving it should be relatively straightforward. It can be avoided by reducing the fruit���s exposure to direct sunlight, especially in the afternoon by preserving shade through judicious removal of leaves around the cluster zone. Highlights ��� ipening disorders are marked by shrivR eling of berries, and the appearance of the shrivel can indicate which disorder is taking hold. ��� he author is an assistant professor at T Washington State University who has studied the disorders closely and gathered photos to illustrate different types. ��� ome berry shrivels such as sunburn S have well-known causes and are easy to avoid; the cause of SOUR shrivel, however, is not well understood.