If not pretreated, these fruits will continue to darken after they're dried. For long-term storage of dried fruit, sulfuring or using a sulfite dip are the best pretreatments. However, sulfites found in the food after either of these treatments have been found to cause asthmatic reactions in a small portion of the asthmatic population. Thus, some people may want to use the alternative shorter-term pretreatments. Sulfuring Sulfuring is an old method of pretreating fruits.
Sublimed sulfur is ignited and burned in an enclosed box with the fruit.
The sulfur fumes penetrate the fruit and act as a pretreatment by retarding spoilage and darkening of the fruit. To locate these, check with your local drugstores or hobby shops, where wine-making supplies are sold. Remove fruit, rinse lightly under cold water and place on drying trays. Sulfited foods can be dried indoors or outdoors. However, its protection does not last as long as sulfuring of sulfiting.