| Abstract | In many developing countries sorghum grain is traditionally processed by the very laborious and time-consuming mortar and pestle pounding method. This process was partially mechanized by the introduction of small grinders in many villages. The trend recently has been toward the construction of larger, centralized facilities which have the capability of cleaning, dehulling and grinding of grain. By the year 2000 it has been estimated (Miche et al. 1980) that if only 20 to 40% of all sorghum produced is processed, some 1000 -8000 medium, capacity industrial plants (3500 tonnes/yr) would be required in Africa. During the last 10 years a great deal of activity has been focused on the development of these village and industrial-scale systems, particularly in countries in Africa. Development agencies such as the FAO and IDRC. government institutions, universities and especially private industry have been very actively involved in is area.
Sorghum grain is processed to remove the fibrous and often highly colored pericarp and testa layers and to reduce the remainder of the seed to flour. Often the peripheral layers also contain anti-nutritional constituents such as tannins. In the traditional mortar and pestle method, and most of the mechanical methods, much of the germ is often retained with the endosperm.
Efficient mechanical dehulling of sorghum has been one of the major problems in the development of sorghum processing facilities and this is an area where most sorghum milling research has been concentrated in the last 5-10 years. The various technologies which have been used to dehull sorghum (or could potentially be used) have been categorized and include: (a) roller-milling equipment and peeling rolls, (b) rice-dehulling equipment. (c) abrasive-type dehullers, and (d)attrition-type dehullers. Many of the machines in the last two categories have been developed specifically for sorghum and similar grains. Approximately 40 dehullers or dehulling methods are reviewed in this paper, the majority (22) being abrasive- or attrition-types. The main objective is to record the major principle of operation of each dehuller (as far as this information is available) and its application to sorghum or a similar cereal. Several commercial- or pilot-scale mills in Africa, most of which have been erected within the last decade are also described. Also discussed is the development of equipment for predicting the milling quality of plant breeders' samples. Since private industry is actively involved in sorghum milling research, much of this information was obtained from unusual sources (advertising bulletins, annual reports, proceedings and internal reports). Hence, some of the information is incomplete. Undoubtedly, some dehulling or mill systems have been overlooked. Other aspects of dry milling not covered here (e.g., grain grinding, air classification, determination, milling products and utilization) have been amply described by others (Hulse et al. 1980; Hahn 1970). |
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