Sun drying of seedless and seeded grapes

Area of Science:

• Food Science and Technology
• Agricultural Engineering
• Drying Technology

Background:

• Grapes are a significant agricultural commodity with diverse applications.
• Drying is a crucial post-harvest process for preserving grapes and enhancing their shelf life.
• Understanding the kinetics of sun drying is essential for optimizing grape processing.

Purpose of the Study:

• To investigate and compare the sun drying behavior of seedless and seeded grapes.
• To evaluate the suitability of various thin-layer drying models for describing grape drying curves.
• To determine the effective moisture diffusivity of grapes during sun drying.

Main Methods:

• Open sun drying of seedless and seeded grapes with initial moisture content around 78-79% (w.b.) to a final moisture content of 22% (w.b.).
• Fitting drying data to 12 thin-layer drying models.
• Statistical evaluation of model performance using coefficient of determination (R²), mean relative percent error (P), reduced chi-square (χ²), and root mean square error (RMSE).
• Estimation of effective moisture diffusivity using Fick's diffusion model.

Main Results:

• Drying times were 176 hours for seedless grapes and 228 hours for seeded grapes.
• The Midilli et al. model demonstrated the best fit for describing the sun drying curves of both grape types.
• Effective moisture diffusivity values were determined as 1.02 × 10⁻¹¹ m²/s for seeded grapes and 1.66 × 10⁻¹¹ m²/s for seedless grapes.

Conclusions:

• Sun drying is a viable method for preserving grapes, with variations observed between seeded and seedless varieties.
• The Midilli et al. model provides a reliable mathematical description for the sun drying of grapes.
• The determined effective moisture diffusivity values offer insights into the internal mass transfer mechanisms during grape drying.