Turmeric (Curcuma longa) drying in natural circulation solar dryer: An experimental evaluation.

A natural circulation solar dryer has been evaluated for drying differently processed turmeric. The predrying treatments namely, hydrothermal treatment using water boiling and steam boiling; and drying methods namely, drying of sliced and unsliced turmeric rhizomes have been investigated. The open sun drying and untreated unsliced turmeric rhizome was used as control. The maximum thermal efficiency of this passive solar dryer has been obtained as 22.4% for the water boiled sliced turmeric, and while that for the steam boiled unsliced turmeric was 14.1%. The thermal efficiency was comparatively lower for untreated turmeric. The quality parameters namely, polishing loss, curcumin content, volatile oil content, total recovery, and color, were found better for steam boiled unsliced turmeric dried in solar dryer. Based on combined perspective of thermal efficiency and quality, drying of unsliced rhizome pretreated with steam in natural circulation solar dryer is recommended as compared to other processing practices. The dryer is economically feasible as indicated by the cumulative present worth of life cycle savings and payback period. Practical Applications: In India, turmeric is an essential part of cuisine. The drying operation consumes maximum time and energy in postharvest processing of turmeric. The conventional practice of drying is open sun. The aim of the article was to find the best drying method and pretreatment method for drying in a natural circulation solar dryer, which will also result in saving conventional energy. It was found that the drying in this solar dryer results in lesser drying time and better quality as compared to conventional method of open sun drying. [ABSTRACT FROM AUTHOR]