2000 Volume 62 Issue 6 Pages 81-91
Drying rate is the common index of drying ability for a continuous flow grain dryer. In developing this dryer, manufacturers in Japan conventionally apply a standard drying rate at which the upper 3% limit for heavy fissure occurrence in heated air drying of rough rice is not exceeded. Until now the allowable upper limit for drying rate has been 0.8%/h. Recently, however, a certain manufacturer commercialized a new dryer with a claim that the rate was doubled to 1.6%/h. Hence the authors carried out basic single-grain layer drying experiments to investigate its possibility. Results showed that varietal differences in fissure resistance were unexpectedly great. Of the five varieties used in the study, Yaeminori was the weakest, with many light fissures occurring even in natural shade drying. Koshihikari was the strongest among the medium grain varieties used since in drying it at a rate of 3.6%/h at 48°C, the 3% heavy fissure limit was not exceeded. In applying this result to practical deep-bed drying, the intended 1.6%/h rate could possibly be realized. For Hitomebore and Tsugaruroman the upper limits to which the rate could be raised were 1.2 and 1.5%/h, respectively. The long grain IR-64 remarkably showed the highest fissure resistance and for this variety the standard rate may easily be doubled.
