Drying characteristics of Malaysian paddy: kinetics & grain cracking quality

• Published in: Drying technology 2005-12, Vol.23 (12), p.2477-2489
• Main Authors: Ng, P.P, Law, C.L, Tasirin, S.M, Daud, W.R.W
• Format: Article
• Language: English
• Subjects: batch dryers; color; cracking; dry milling; drying quality; drying temperature; grain dryers; Grain fissuring; Head rice yield; Milling; Rough rice; water activity; water content; yield components
• ISSN: 0737-3937; 1532-2300
• DOI: 10.1080/07373930500341724

Drying kinetics of Malaysian paddy dried in a laboratory scale batch rapid bin dryer was studied. Quality of paddy after drying at temperatures of 60 and 80°C, bed heights of 2 and 4 cm, and at different drying stages was presented in terms of cracking percentage. Moisture content of paddy reduced exponentially with time and became stable at equilibrium moisture content. Characteristic drying rate curves exhibited mainly falling rate period, with an induction period in deep beds, but without the constant rate period. A custom-made light box was built to visually analyze the cracking in paddy kernel. The extent of breakage is directly related to the crack percentage. The percentage of cracks increased with drying and tempering temperatures and was higher after 2 weeks of storage before milling. Bed heights did not significantly affect the head rice yield as much as tempering between two drying stages. Temperatures above 80°C caused severe cracking in paddy kernel and produced miserable yield of head rice after milling, which could be slightly improved by tempering. The use of a proper miller is also important in ensuring good head yield results and whiteness quality.