The role of solar energy in the drying of vine fruit

Abstract

In Australia grapes are dried almost exclusively by natural energy on tiered racks usually sheltered by an iron roof. Under these conditions it was shown that there is a close relationship between direct solar radiation and rate of drying. Wavelengths of 0.7 to 0.9 µ, which are abundant in sunlight, penetrated grape skins, particularly after (cold) dipping treatments, and temperatures within the grapes in excess of 8°C above air temperatures were frequently recorded. The quantity of water evaporated from grapes on a weighed drying rack approximated closely to estimates based on simultaneous measurements of solar radiation. The efficiency of tiered drying racks was superior to that of two types of low cost air driers in which solar energy absorbers were used.