Effect of mixing different paddy samples and aeration on the head rice recovery

It is a common practice in commercial rice mills to buy and mix different small rice lots in order to get the quantity required to operate a dryer and the mill with the required capacities. This often results in mixing rice lots of different moisture contents (MC) which leads to re-absorption of moisture by the paddy grains from the lot with the higher MC. Research has shown that moisture re-absorption is a main cause for development of fissures in paddy, resulting in more broken during milling. The loss of head rice will increase with the increase in the moisture difference in the paddy lots. For high head rice recovery some of the dryer manufacturers recommend mixing and/or aerating of the paddy with ambient temperature for a specific time before turning the heater on and starting the actual drying process. The experiments described in this paper were conducted to verify the positive effect of mixing combined with aeration claimed by the dryer manufacturers on head rice recovery. It also evaluates the potential for additional cracks developing during aeration periods due to dry grains absorbing moisture from the wet paddy. To assess the extent of head rice loss due to mixing paddy samples with two different MC, mixed MC samples and samples with layers of different MC were dried under controlled conditions in a laboratory dryer available at IRRI. The time taken for drying to the safe moisture content (14%) was determined and the drying rate curves were drawn. The drying was done at constant climate conditions of temperature (55 deg C) and relative humidity (25%) similar to the drying air conditions found in commercial paddy dryers. The air conditions found in commercial paddy dryers. The air flow rate was maintained constant for all the treatments. To determine the effect of aeration with ambient air prior to drying on head rice the samples were aerated for 0, 30 and 60 minutes prior to drying. The dried paddy was analyzed for brown rice yield, brown rice whiteness, milling yield, whiteness, head rice and chalkiness. The rapid visco analysis of samples was done to assess the cooking quality of samples. Results show that aeration prior to drying had a slightly positive effect on head rice recovery.