MEETING ABSTRACT
S-28
Recent advances in rice drying technology. T. Siebenmorgen. University of Arkansas, Fayetteville, AR.
One of the primary tenets of rice drying research conducted over the past decade as part of the University of Arkansas Rice Processing Program is that "commercial rice drying will not be significantly improved unless we understand what occurs inside individual kernels during drying". Towards this goal, basic research of this Program has quantified the thermal and mechanical properties of individual rice kernels over a wide range of temperatures and moisture contents. In particular, the glass transition temperature (T(g)) of brown rice kernels has been measured over a range of moisture contents, allowing a rice T(g) vs. moisture content state diagram to be constructed. Further, the pathways that kernels might follow during the drying process, to include actual drying and subsequent tempering, have been plotted onto the state diagram. Of equal importance, the internal kernel temperature and moisture content gradients that could occur during the drying process have been postulated. Using this information, the "glass transition hypothesis" has been formulated to predict the onset and cause of kernel fissure development. This approach to rice drying research reveals two processes that produce fissures and reduced milling quality; extended drying and rapid cooling upon termination of drying. The glass transition hypothesis will be presented, along with laboratory results and unique, commercial-scale, cross-flow column drier tests that support the postulated causes of milling quality reduction. More recent laboratory research utilizing the glass transition concept will be presented that builds upon the commercial drier tests. This research was conducted to minimize milling quality reduction in cross-flow driers and to help implement high temperature, thin layer, rapid drying techniques. Such techniques are being utilized in fluidized bed drying systems that are being introduced in many rice-producing countries. These systems will be described, as will be the results of this recent laboratory research.