9.1 Quality and grading of commodities
9.2. Maize grain grade specification
9.1.1 The value of grading standards
Most countries have developed national maize standards, aiming to provide a framework for trade, both internal and external. Where trading involves direct choice and price negotiation in front of the commodity, grading standards are rarely employed; quality is assessed visually and is influenced by end-use, and the price is determined more by local rather than national factors. For regional transactions that involve the movement of large volumes of maize over long distances, the buyer may never meet the seller or be able to examine the whole consignment. The use of an agreed standard will provide an unambiguous description of the quality of the consignment and assist in the formation of a legally-binding contract. Standards can also be seen to protect consumers rights through setting limits to the amount of unsuitable or noxious material.
Whilst establishment of standards can set the, guide-lines and rules for sale and purchase of maize, there has to be an institutional framework for their implementation. This is much easier to establish at centres of aggregation of grain e.g. ports, parastatal grain depots, than in the more diffuse rural areas and markets, where control and supervision of regulations is difficult.
9.1.2 Advantages of grading standards
Notwithstanding these problems, the establishment of quality and grading standards for producers and users can be beneficial in the following ways:
9.1.2.1 Graded maize is likely to be more equitably priced than non-standardized maize. This will bring stability not only to market prices but also to the quality offered.
9.1.2.2 Prices quoted against a recognised grade assist producers and traders to assess and market their products. This will also benefit net consumers of maize in more stable prices with assured quality.
9.1.2.3 Greater conformity in quality through standardisation will provide the processors with the consistency necessary for optimum performance.
9.1.2.4 Standards reveal clear variations in quality and indicate the opportunities for improvement and the potential rewards to be obtained.
9.1.2.5 The sanitary hazards associated with the inter- country movement of grain can be reduced if clear defined standards are enforced, particularly in relation to the prevention of serious storage pests like the Larger Grain Borer, (LGB).
9.1.3 Disadvantages of grading standards
However, the use of standards can have its disadvantages or present problems, namely:
9.1.3.1 National standards may reflect local end-uses and hinder export to areas that have differing requirements. Whilst restricting opportunities for commercial trade, this can also be detrimental for regional food security. The stimulation of regional trade would require inter-country conformity in export standards. Also standards for export may have to be more stringent in relation 10 physical conditions such as defective grains and insect infestation, than that for national use.
9.1.3.2 The establishment of standards and the quality assurance practices to regulate and enforce them carries costs which have to be carefully considered to avoid imposing unnecessary expense for little improvement in quality.
9.1.3.3 Confusion an difficulties may arise where standards vary significantly between countries. This may be a particular problem for procurers for regional maize food security reserves which require both uniformity and good quality.
9.1.4 Maize Quality
To safeguard consumers' rights most countries have established regulatory standards which gives details of the criteria of quality that must be meet to ensure entry of the commodity. The criteria assigned to commodities are the intrinsic varietal qualities combined with those which are environment-or process-induced. The more important quality criteria as they relate to the grading of grain are:
9.1.4.1 Intrinsic Qualities
· Colour
· Composition
· Density
· Odour/aroma
· Size/shape
9.1.4.2 Induced Qualities
· Age
· Broken grain
· Chalky and immature grain
· Foreign matter including odour, pesticide residues
· Infested/infected including damaged grain
· Moisture content
· Mixed varieties
Standards are established for a variety of purposes but mainly:
a) for produce grading in agricultural marketing, both internally and for export or, increasingly,
b) for the protection of consumers.
The requirements of the two groups are not necessarily compatible.
9.1.5 National requirements
It could be argued that a commodity standard should be country specific, containing factors such as percentage brokens, foreign matter, moisture content that reflect the types of end use, be it for commercial or domestic purposes. Liberalization of the grain market may mean that domestic quality standards are abolished and it is up to the buyer/seller to decide on quality control and hence a quality standard may be necessary.
9.1.6 Regional requirements
End usage, and hence standards, may vary from one country to the next. Where standards vary considerably between countries, the movement of grain may be hindered. A country may have a single standard that covers both internal and external grain movement. This may not facilitate the trade of a commodity between countries, particularly if the standard permits a greater degree of defective grains than its potential trading partner.
Regional food security may be impaired if the quality of the commodity is not acceptable to some of the countries in the region. Therefore a quality grading standard, acceptable to all users, would be necessary for a commodity stored as part of a regional food security programme.
9.1.7 International trade
International trade of grain is possible without a standard, if buyer and seller are aware of each others requirements. However when country specific knowledge and requirements are not known, a standard will provide the guide-lines that ensure the maintenance of quality, and safeguard consumers rights.
9.2.1. Scope
This standard specifies the rules for the classification and grading of shelled, unprocessed maize (Zea mays L) intended for human consumption.
9.2.2. Definitions
For the purpose of this standard, the following definitions shall apply.
9.2.2.1 Foreign matter; any material which is not maize grains or parts of maize grains.
9.2.2.2 Broken maize: maize or fragments of maize that will pass, with thorough shaking, through a 6.35 mm (16/64-in) diameter round hole screen (also described as a "6 sieve").
9.2.2.3 Pest-damaged maize: maize grain which have been damaged by insect and animal pests.
9.2.2.4 Diseased maize: Maize grain which has a visible growth of fungal mycelia on its surface. Those grains which show rotting without having to split open the kernel.
9.2.2.5 Detective maize: Maize grains which are stained, discoloured, shrivelled or immature, germinated or sprouted.
a) stained grains are those whose natural colour has been altered by external factors such as soil, smoke, coal, dust or by any other means.b) discoloured grains have changed colour due to heat, fermentation, weather damage (e.g. frost). Kernels may appear darkened, wrinkled, puffed, blistered or swollen. The germ may be discoloured (though not due to disease) and the seed coat peeling or may have peeled off completely, giving a chequered appearance.
c) shrivelled or immature grains are underdeveloped, thin and papery in appearance. This extends over the entire grain surface and not over the germ only. It does not include "tip" or "butt" maize which is small and unwrinkled.
d) germinated or sprouted grains are those in which the process of germination is visible within the germ, with a crack in the seed coat through which a sprout has emerged or is just beginning to emerge.
9.2.2.6 Other-coloured maize grains: maize grains which have a natural colour that differs from that of the type of maize grains which the bulk sample represents.
9.2.3 Classification
Maize shall be divided into the following classes:
9.2.3.1 White maize (WM): maize grains which are white and/or light pink in colour are considered to be white. A slight tinge of colour other than white that does not cover more than 50% of the grain surface shall not affect the classification of the maize. Maize grains of a contrasting colour should not be present above the level indicated in Table 1.
9.2.3.2 Yellow maize (YM): maize grains of yellow and/or light red or orange are considered to be yellow maize. A slight tinge in colour other than yellow that does not cover more than 50% of the grain surface shall not affect the classification of the maize. Maize grains of a contrasting colour should not be present above the level indicated in Table 9.1. Maize may be present as flint, dent or a mixture thereof.
9.2.4. Grade requirements
In addition to the quality requirements specified in Table 1 below, maize shall be:
1) free from musty and objectionable odours;2) free from poisonous chemical substances, residues and heavy metals in amounts which represent a hazard to health; .
3) free from live insects and other pests irrespective whether such pests appear within or on the grains, in or on bags containing the maize or in a bulk container;
4) free from rodent droppings.
9.2.5. Methods of inspection and analysis
9.2.5.1. When the sample arrives for inspection, it must be divided into a work sample, a moisture sample and a file sample. It is important that all three samples must be representative of the original sample. Whenever a sample is divided or a portion is removed for further analysis, a Boerner divider, or a divider that gives equivalent results, must be used. The sample reduction procedure must be repeated until a portion of the desired size is obtained. This portion must be used in its entirety in the subsequent analysis.
TABLE 9.1: Grading Standards for shelled maize
|
Gram characteristics |
Maximum limits (%) |
|||
|
Grade |
||||
|
WM1 |
WM2 |
YM1 |
YM2 |
|
|
Moisture content |
12.5 |
12.5 |
12.5 |
12.5 |
|
Foreign matter |
0.5 |
1.0 |
1.0 |
1.5 |
|
Broken maize |
3.0 |
5.0 |
5.0 |
8.0 |
|
Pest-damaged maize |
4.0 |
7.0 |
4.0 |
7.0 |
|
Diseased maize |
2.0 |
2.0 |
2.0 |
2.0 |
|
Defective maize |
2.0 |
4.0 |
2.0 |
4.0 |
|
Other coloured maize |
3.0 |
6.0 |
2.0 |
5.0 |
9.2.5.2. File sample: this sample, minimum amount 1 kg, is stored in a moisture and insect proof container and retained for up to 120 days depending on the movement of the sample from which it was drawn. It is to be used in the case of disputes.
9.2.5.3. Moisture sample: this sample, minimum 250g, is stored in a moisture-proof container until moisture analysis is carried out. The sample size is obtained by using a divider such as the Boerner type.
9.2.5.4. Work sample: this sample is used to determine the factors on which the grades are determined. The working sample must not be less than 1 kg: some of the factors are determined on a representative portion of a prescribed size (see below) that has been removed from the work sample by using a Boerner divider.
9.2.6. Inspection and analysis
9.2.6.1. The examination procedure to determine grade factors is given in Chapter 4.1.11; Figure 4.4.
9.2.6.2. The entire work sample of 1 kg is placed on an open clean white tray (approximately 50 x 775 cm, with a 10 mm high retaining edge). The sample is inspected for unusual conditions and the grain smelt to determine whether its odour is natural or whether it is musty, sour or commercially objectionable. It is examined for the presence of live insects.
9.2.6.3. The working sample is divided by a Boerner divider to give a sample of not less than 500 g which is then weighed (to the nearest 0.01 g) and screened through a No 6 sieve with 6.25 mm round holes. The sample that is retained on the sieve is poured on to a clean white tray for inspection.
9.2.6.4. Determination of infested, diseased, defective and other-coloured maize: maize grains which exhibit these characteristics are hand-picked from the sample portion retained in the sieve. The maize assigned to each grade factor is weighed and the amount is then calculated as a percentage of the total sample taken for screening.
9.2.6.5. Determination of broken grains: broken grains shall be hand-picked from the material that passes through the screen and weighed. The amount of broken grains is calculated as a percentage of the weight of the total sample taken for screening. Shrivelled or undersized maize grains are also removed and retained separately to be added to those maize grains which are graded as defective maize.
9.2.6.6. Determination of foreign matter: foreign matter is handpicked from the portion retained in the sieve and added to the foreign matter passing through the sieve, this is then weighed. The amount of foreign material is then calculated as a percentage of the total sample taken for screening.
9.2.7. Grading
After the sample has been analysed for all factors, it is assigned a grade equal to the lowest grade determined for any of the factors.
9.2.8. Fair average quality (FAQ)
9.2.8.1. Some grain-exporting countries sell under a system called "fair, average quality".
9.2.8.2. Under this system, a representative sample of maize is obtained as a vessel is unloaded at the port of destination. Samples from all shipments arriving under a FAQ contract from a particular origin are sent to the same inspection office, where a committee made up of representatives of both buyers and sellers compares all samples for the month from each origin port. This is mostly by visual inspection to determine average quality. When agreement is reached, the lots of median or average quality may be further tested, then pooled, retested, and used as a quality standard.
9.2.8.3. This becomes the FAQ standard for the month for lots arriving from a particular origin. Lots are priced according to whether they are better or poorer quality than the FAQ standard. Thus, the FAQ at a particular port of destination differs by port of origin and from month to month.
9.2.8.4. The advantage to the buyer of the FAQ system is that payment is based on quality received that month which includes quality changes that have resulted from transportation and handling. However, the month to month quality changes that may occur introduces uncertainty about future quality; uncertainty is reduced using grade-specific contracts.
