Drying-cum-parboiling of paddy by conduction heating | |
| Author | Dash, Pabitra Kumar |
| Call Number | AIT Diss. no.AE-89-01 |
| Subject(s) | Rice--Drying Rice, Parboiled |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. AE-89-01 |
| Abstract | Drying-cum-parboiling of soaked-paddy by high temperature conduction heating was studied as a means of eliminating the steaming operation in the conventional parboiling process. Experiments were carried out with an electrically heated prototype rotary dryer by recirculating a batch of paddy continuously and monitoring the changes in grain moisture and temperature. In addition, changes in grain quality in terms of starch gelatinization, head rice yield, mille rice whiteness, white-belly grains and cooked-rice hardness were subsequently evaluated. Conventional steam-parboiled paddy was also dried under similar test conditions for making direct comparisons in grain quality and the energy requirements. A three-stage paddy drying-cum-parboiling operation with tempering of grain for 1 hour after each test yielded best results. Paddy having initial moisture content of about 30% w.b. was dried to final moisture content in the ranges of 21.8 to 22.9% w.b., 17.7 to 19.0% w.b. and 13.5 to 14.0% w.b. during first, second and third-stage operation, respectively. Drying of paddy in all tests was adequately represented by a simple logarithmic model. Generalized drying models were developed later in terms of mean bulk grain temperature determined from the time-temperature history in any given conduction beating equipment. Gelatinization of starch in rice grains was complete during initial 15 minutes of drying and corresponded to a final moisture content of about 24% w.b. in all tests. However, grain temperatures attained close to 80ฺC resulted in parboiling comparable to steam-parboiled paddy. Conduction parboiling appeared to be better than stem-parboiling based on milled rice whiteness and heat-damaged grains but indicated the presence of white-belly grains against none in steam-parboiled rice. Steam-parboiled paddy having initial moisture of about 33 to 34% w.b. could be dried in a three-stage operation with final moisture content limits of about 20, 17 and 14% w.b. for first, second and third-stage drying, respectively for minimum reduction in head rice yields. The developed drying models based on mean bulk grain temperature determined from the time-temperature history appeared to be satisfactory for general application. The energy requirements for producing 1 ton of parboiled paddy using the proposed drying-cum-parboiling and conventional steam-parboiling processes were estimated to be 323.4 and 394.5 kWh, respectively indicating the considerable energy savings and potential applications of the proposed method. |
| Year | 1989 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. AE-89-01 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural and Food Engineering (AE) |
| Chairperson(s) | Jindal, V. Kumar;Ilangantileke, S. G.; |
| Examination Committee(s) | Athapol Noomhorm;Prida Wibulswas; |
| Scholarship Donor(s) | Government of Japan; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1989 |