One cause of yellowing or stackburn of rice may be elevated respiration rates caused by storage at either high moisture content (MC) or temperature. The effect of MC and temperature on the respiration rate of Oryza sativa L. 'Bengal' and 'Cypress' rice harvested in the fall of 1998 was investigated. For respiration rate measurement of rough rice at different temperatures, rice samples at high, medium, and low MC were sealed in quart jars and equilibrated to temperatures of 20-80 degrees C. The respiration rate was quantified by measuring the rate of CO2 accumulation in the free air space. To determine the effect of MC on respiration rate, rough rice was tested at 12-25% MC. Respiration was greatly affected by MC and temperature. The response of respiration to temperature was dependent on MC and varied between rice cultivars. Respiration rates increased as MC increased from approximate to 15 to 25%. Maximum respiration was at 50 degrees C when MC was high (20-25%). At 15% MC, respiration increased from 20 to 70 degrees C, while respiration of 12% MC rice, although very low, appeared to increase up to 80 degrees C. A model was developed from this data to predict the respiration rate of rice over the MC range tested.
