Improvement in commercial sun-drying of parboiled paddy for better milling quality.

Relationships between sun-drying conditions and milling damage to parboiled paddy were investigated. Long-grain Kalma rice was parboiled and dried. Moisture and temp. were measured during drying and samples examined for milling damage. During 2-stage drying, portions were collected at desired moisture contents into cone-shaped heaps of approximate equal to900 kg, covered with thick straw caps for tempering (3-4 h or overnight), then dried to completion. The remaining portion was dried continuously, sampled immediately after drying and after 3-4 h storage in covered heaps (post-drying hot storage). Damage to milling quality did not occur at moisture contents greater than 16%, but increased progressively and sharply with lower moisture contents, but was reduced by hot storage or by tempering. After 1-stage drying, % broken grain in milled rice was 22.3, with a final moisture of 13.2%; 36.5 with 12.5% final moisture; and 13.4 when using hot storage. After 2-stage drying, % broken grain was 5.2 with tempering at 15.8% and drying to 12.1% final moisture; and 7.0-7.9 with tempering at 15.3-15.8% and final moisture of 12.8-12.9%. Working directions for 2-stage drying with tempering at 16% moisture are given.