Improvements of the SO2 Technology for Extended Storage of Table Grapes
2010
Lurie, S. | Zutahy, Y. | Kaplunov, T. | Lichter, A.
The SO2 technology is the current practice for storage of table grapes. While it has been under scrutiny in the last decade and there is a constant demand for alternative technologies, it remains the only established method for extended storage of table grapes. We present 3 tools which improve the efficiency, longevity and accuracy of storage of grapes with SO2. Most of the industry is packaging grapes in cartons containing liners in which dual release SO2 sheets are placed on the grapes. This packaging confines the SO2 to the clusters but it compromises the efficiency of forced air cooling. The alternative method is to avoid the use of liners and to wrap the pallet with polyethylene stretch film. This process reduces forced-air cooling time, saving energy and a considerable amount of plastic packaging material. The level of SO2 in the pallet is low because the pallet's bottom is open and the quality of the rachis is high because the humidity in the pallet is high as well. Adoption of this technology for extended storage of 'Red Globe' grapes stored in plastic boxes, by closing the bottom of the pallets, proved to be problematic due to high levels of SO2 and short duration of release. By placing the SO2 releasing sheets in plastic bags containing holes in the bottom, it was possible to extend the storage from 3 month to 4.5 month with satisfactory quality and levels of sulfites within the grapes that did not exceed the threshold of 10 mg kg-1. To improve the quality of the process we developed an analytical method to measure the rate of SO2 released from the SO2 sheets. These 3 methodologies are practiced on a commercial scale enabling storage of table grapes of consistent quality.
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