Grinding characteristics of cryogenic and ambient ground dried ginger at different moisture contents

Abstract

Ginger (Zingiber officinale Roscoe) is a widely used spice in India, valued for its culinary and medicinal properties. During conventional grinding using hammer mills, the product temperature rises significantly, resulting in the loss of volatile compounds, oleoresins, and colour. To overcome these drawbacks, a cryogenic grinding system was evaluated and compared with ambient grinding. Dried ginger samples of three moisture contents (7%, 12%, and 18%) and three slice thicknesses (1.5 mm, 3 mm, and 4.5 mm) were prepared, yielding nine sample combinations. Preliminary grinding experiments were conducted at ambient temperature using a small-scale grinder to evaluate power consumption, fineness modulus, and colour values. The best performance was obtained for ginger slices of 1.5 mm thickness and 7% moisture, with power consumption of 65 W, fineness modulus of 5.04, and colour values of L* = 83.7, a* = 2.8, b* = 33.84. This optimized condition was further evaluated in large-scale ambient and cryogenic grinding using a hammer mill. Cryogenic grinding consumed less power (960 W) than ambient grinding (1440 W) and produced lighter, more colour-stable powder (L* = 89.79, a* = 3.88, b* = 32.08). The volatile oil yield was also higher under cryogenic conditions (1.0 mL per 50 g) compared to ambient grinding (0.75 mL per 50 g). The fineness modulus was 4.34 and 4.5 for cryogenic and ambient grinding, respectively, indicating finer and more uniform powder in the former. Overall, cryogenic grinding enhanced product quality through lower energy consumption, improved colour retention, and higher volatile oil yield.