EFFECTS OF VARIOUS TREATMENTS ON THE DRYING KINETICS OF Muscatel GRAPES

ABSTRACT

The drying kinetics of Muscatel grapes at 60°C and a relative air humidity of 22% were determined after various pretreatments had been applied to the grapes. The pretreatment parameters varied were the chemical agent (potassium carbonate solution with or without olive oil, or sodium hydroxide solution); the duration of pretreatment; and the temperature and concentration of the solution. A 3 minute pretreatment with an aqueous solution of K₂CO₃ and olive oil at 60°C reduced drying time from about 80 h to 20 h. Optimal drying load corresponded to a single layer of almost close-packed grapes on each tray. The experimental drying kinetics were satisfactorily reproduced by a model in which both grape size and the effective coefficient of diffusion are functions of moisture content.

Key words and phrases:

• Vitis vinifera L
• drying
• diffusional model
• volumetric changes
• effective coefficient of diffusion