In this article:
The various physical factors involved in the drying of sultana grapes have been determined from measurements of drying rate under definite conditions of temperature, humidity, and air flow, in a specially constructed oven.
Drying is found to occurs in three distinct stages: (1) the grape retains its regular ellipsoidal shape by an elastic contraction of the skin; (2) the skin commences to wrinkle in the range of 20-50 per cent, loss in original weight; (3) the drying rate decreases markedly, beginning when approximately 95 per cent. of total loss of weight has occurred and when probably all the free water has been removed from the system.
The ways in which water movement occurs, and effects of the waxy cuticle and elastic retration of the cuticle, are discussed.
The rate of drying is found to increase rapidly with rise in temperature owing to the vapour pressure of water and the permeability of the cuticle increasing with the temperature.
The Physical Factors Involved in the Drying of Sultana Grapes
1957, Australian Journal of Agricultural Research, vol 8, issue 5, pages 544 -549
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