|Small-Scale Maize Milling (ILO - WEP, 1984, 160 p.)|
|CHAPTER II. GRAIN PREPARATION|
A number of operations must be carried out prior to the milling of maize grain, including the following:
- harvesting of the maize cobs;
- drying of cobs prior or after husking;
- shelling; and
- storage of dried grain whenever necessary.
The above sequence of operations may be altered by, for example, shelling the cob after harvesting or husking, then drying the shelled grain for storage. The drying of maize before shelling is recommended whenever it must be stored over a prolonged period of time before milling since the leaf sheaths protect the grain against insect infestation and breakage. On the other hand, the drying of maize on the cob requires a longer drying time than that of shelled maize. Thus, the decision to dry the grain before or after shelling will depend to a large extent on its ultimate use.
The various operations preceding milling are briefly reviewed in this chapter, with the exception of shelling which is described in detail in Chapter III. Since this memorandum is mostly concerned with milling technologies used in small-scale production units (custom and merchant mills), a number of the operations listed above may not be carried out by these units. For example, custom mills usually process the dried grain brought by the customers, and do not engage in husking, shelling or drying of maize. However, it is conceivable that some small-scale mills, particularly merchant mills located in urban areas, may carry out some of the operations. This is the reason for including this chapter on grain preparation. However, since a separate memorandum on grain storage and drying is also being prepared, these two operations will not be covered in detail in this chapter.
Small-scale mills may undertake the various operations which precede milling according to one of the following five sequences:
- Husking - drying - storage on the cob - shelling as required;
- Husking - drying - shelling - storage as shelled grain;
- Husking - shelling - drying - storage as shelled grain;
- Drying - husking - storage on the cob - shelling as required; and
- Drying - husking - shelling - storage as shelled grain.
Depending on circumstances, one or the other of the above sequences may be preferred. Weather conditions, availability of storage, and the duration of the storage period, the price and availability of fresh or dried cobs, etc. will generally dictate the choice of the most appropriate sequence.