Grapes to be shipped as fresh are packed in wooden crates, then pre-cooled to about 40 ° F (4.4 °C) in railroad cars or refrigerated rooms.
The fruit can tolerate temperatures slightly lower than this, but the margin of safety above freezing the grapes becomes so narrow that for practical purposes, this temperature should he considered the minimum.
Generally, the grapes will be fumigated with sulfur dioxide prior to or during cooling to prevent mold growth. Sulfur fumigation after harvest and /or used of grapes guards have been shown to reduce postharvest losses significantly. The fungus may infect berries in vineyards, particularly when extended periods of rainy weather occur before harvest.
Sulfur dioxide is produced by burning elemental sulfur. It is lightly toxic to fungi and bacteria. The toxicity increases with the percent relative humidity. The relative humidity of the air should be as high as practicable – 95% if possible.
Grapes that are to be stored for future shipment should be packed in crates, pre-cooled to 36-40 °F (2.2 - 4.4 °C), place in refrigerated storage 29- 32 ° F (-1.67 – 0 °F), and fumigated with sulfur dioxide and should be held in this manner until shipped.
Periodic re-fumigation with sulfur dioxide may be required to prevent spoilage by molds.
Grapes storage and fumigation