An Investigation of the Drying Methods and their Effects on Milling Quality of Rice in Guyana

Rice is the largest agricultural crop produced in Guyana. There are various post-harvest operations for rice, which include: threshing, cleaning, drying, milling, storage, transportation and marketing. Post-harvest losses can occur during any one of these operations. Drying reduces the moisture content (MC) of the grains for milling and storage. It is one of the most critical factors that contribute to both qualitative and quantitative losses; these include: yellowing or discolouration caused by mold development and heat build-up from respiration, and reduced head rice recovery. Despite the importance of this operation to losses, no work has been done on the various drying systems in Guyana. This study seeks to investigate the drying methods used in Guyana’s rice growing regions and determine the effects of these methods on the milling qualities of rice. All operable mills were selected in Regions 2, 3, 4, 5, and 6. A survey was carried out using a questionnaire during the harvesting period and 1000g of paddy samples were collected in replicates from each mill after drying was completed. The average percentage of fissure kernels and the milling yield was determined in the laboratory. Two drying methods were used in Guyana: sun drying and mechanical drying. There were various types of mechanical dryers; the column dryer (44.4%) was the most popular among millers. Prior to drying, only 37% of the millers group their paddy according to moisture content (MC); however, during the drying, 81.5% monitored MC. The final MC of the grains significantly affected the percentage of fissure kernels and the overall milling yield (P=0.001). There were no significant differences in the average fissure kernel percentage and milling yield of samples collected from the sun and mechanical drying methods (P=0.598 and P=0.185); however, sun drying was affected by several parameters such as the thickness of the paddy on the drying floor, final moisture content, weather and labour availability.