We are a refrigeration contractor specializing in horticultural cooling. One of our clients [a grape grower] has enquired about the availability of SO2 pads or SO2 gas to be placed in his containers packed with grapes for export. I would imagine this to be a slow release gas or slow release pads - maybe the cylinder is placed in the container on loading and left in the container for the duration of the trip. Can you suggest a product and or a supplier for a suitable product? (D.R.)
There are two general types of pads, a slow release design and a two-stage system. Slow release design is for grapes that have been SO2 fumigated at least once before shipment. The other system provides an initial rapid release of SO2 for an initial fumigation and a slow release for long-term storage. The slow release pad and the two-stage pad will protect grapes for at least one month. It is possible to release SO2 into the container from a bottled source. This will simulate an initial fumigation. However grapes need to be re-fumigated once every seven days during storage. If the trip is longer than 7 days, then the product will need to be retreated during transport. I know of no commercially available systems that will release controlled doses of SO2 on a weekly basis. I hope this is helpful.