ABSTRACT Black pepper (Piper nigrum L ) was ground to different particle sizes at ambient conditions, and the ground material temperatures at the mills’outlet were recorded. The surface mean diameter (d s ) and geometric mean diameter (d ga ) of the pepper grits were determined by sieve analysis. Energy for size reduction was computed using Bond's equation. The quantity of essential oil distilled, using Clevenger's method, was recorded at 30 minutes interval for each particle size. Effective diffusion coefficient (D) determined using Fick's second law, was constant (1.38 × 10 −11 m 2 s −1 ) for higher oil concentrations and it was very less in lower oil concentrations. The essential oil yield was evaluated in terms of four major compounds using gas chromatographic analysis. The particle size (d go ) of about 0.7 mm was found to be optimal for distillation of essential oil.
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