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Project Record

Improvements to the processing of sorghum, especially for non-traditional uses: DEHULLING

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 Food Science and Crop Utilisation
 Central Research Department (now Research and Evidence Division)

  Global, Africa, Eastern Africa

The objectives of the project are:
To improve food security in the semi-arid tropics by encouraging improvements and processing of sorghum.
(i) Small scale dehulling equipment
Collaborative work has continued on the development of the NRI experimental dehuller for sorghum, and this is being tested at ICRISAT in Zimbabwe during the last quarter of 1991/92.
The NRI machine is a test rig which will provide information for the design of a superior machine to the PRL model: the trials at ICRISAT are intended to compare the two machines.
Grain cleaning prior to processing is an essential requirement in order to provide an uncontaminated product for consumption, free from, in particular, stones the same size and colour as the grain. Commercial destoners are far too large to be used with the PRL and NRI dehullers. A simple grain cleaner based on the vacuum-cleaner principle has therefore been designed and built by NRI and will also be tested in Zimbabwe.
(ii) Laboratory Scale Dehulling
The small dehuller which NRI built several years ago has not been bettered as a laboratory tool for producing small quantities of dehulled material for further processing. It has a very useful capacity when the grain sample size is limited. It does, however, have limitations which could be overcome with design modifications. In essence, the dehulling chamber needs to be redesigned to improve the exposure of the grain to the dehulling action to make it more efficient. As well as improving the dehuller for NRI laboratory operations, the modified unit would be described in a technical paper and included in the ICC study of laboratory equipment for sorghum processing.

Optimisation of the general purpose mill for sorghum dehulling.

Optimisation of the precleaner for the removal of stones the same size as sorghum grain.

Modifications to general purpose mill and precleaner.

Construction of a laboratory scale dehuller.

Traditional dehullers for the removal of fibrous bran layers of sorghum utilise imported high cost carborundum grinding discs as the abrasive dehulling surfaces. An alternative machine utilising adhesive or re-machinable abrasive surfaces has been designed and evaluated on a range of sorghums for use as a dual-purpose batch dehuller/grinder. The new dehuller has been designed for peri-urban use in semi-arid areas, and also allows coarse flour to be produced. Low cost replaceable surfaces are as effective as carborundum stones for dehulling hard-textured varieties of sorghum. Soft sorghums are prone to disintegrate. Full machine drawings and costings are available for use by potential fabricators. A laboratory scale dehuller was also constructed for use by sorghum breeders and process technologists for the evaluation of dehulling characteristics of different varieties of sorghum.

The dehulling characteristics of several sorghum varieties gave been evaluated using the prototype machine. Knowledge of the relationship between variety and dehulling characteristics will enable farmers to select sorghum varieties with desirable processing qualities.