Grain standards

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The term 'standard' used in the present context refers to the measures that serve as a basis for making comparisons or judging the accuracy of unknown samples. Three types of standard will be covered in this chapter:

Standards are established for a variety of purposes but mainly: a) for produce grading in agricultural marketing, or, increasingly, b) for the protection of consumers. The requirements of the two groups are not necessarily compatible.


Standard Specification for Grain

There are at least 330 specifications for cereals and cereal products at national and international level (over 50 countries or regions) of which at least 12 are applicable globally. Standard specifications provide criteria to characterize the nature of a commodity, usually on a pass or fail basis.

Most countries have a national standards institution which may issue specifications for commodities as well as methods of testing. Many countries adopt or modify international standards, e.g. International Organization for Standardization (ISO) standards, into their national system. Another source is the Codex Alimentarius Commission (Codex) which operates a committee to formulate standards on cereals, pulses and legumes.

Tables 3.1 (see Table 3.1. European Community Intervention Regulations on Minimum Quality Standards.) and 3.2 (see Table 3.2. Ethiopia - Grain Grading Standards.) show examples of trading-bloc and national standards, and Tables 3.3 and 3.4, examples of international standards.

Table 3.3 shows the ISO standard specification for wheat: a sample is judged against the standard, and may be referred to as wheat if it passes all the criteria listed.

One notable feature of the standards in Tables 3.1 to 3.4 is the difference in tolerance of mc. Both of the quoted international standards allow 15.5%, whereas the European Community (EC) and Ethiopian standards have lower values, 14.5 and 14.0% respectively.

In the cited examples, not only do we have the potential for mix-interpretation but also, more seriously, the basis for deterioration of the product. For example, take the case of maize with 15.0% mc loaded into a ship in northern latitudes at 4C. Calculated from data presented by Foster (1982), such grain would have an inter-grain equilibrium relative humidity (ERM) of approximately 65 % which is normally regarded as safe. However, if the grain is unloaded in a tropical country with an ambient temperature of 32C, its inter-grain ERH becomes 75% - too high for safe storage.

Boxall and Gough (1992a and b) monitored shipments of food-aid maize grain from north America to southern Africa. They reported that heating and mould-damage took place when the grain was stacked at port of discharge, and confirmed that the standard mc of 15.5% at loading was too high for the conditions at the destination. A second shipment of grain dried specifically to approximately 14.5% mc suffered damage as well. In comparison, an intraAfrican importation with 12.2% mc did not suffer heating or deterioration on storage. Studies are continuing at NRI on the importance of integrating quality standards between suppliers and consumers.

The problems associated with moisture content may be harmful to international trade in grain and need to be addressed adequately by the standardisation institutions. ISO 7979 (Table 3.3) goes some way towards this by acknowledging the principle of destinationspecific mc though without defining appropriate action.


Standard Test Methods

There are at least 420 standard test methods for cereals and cereal products at national and international level (over 50 countries or regions) of which at least 75 are applicable globally.

As with the specification of cereals, many countries modify or adopt international standards, e.g. International Organization for Standardization (ISO) standards, into their national system. Another important organisation, particularly for the development of testing methods, is the International Association for Cereal Science and Technology (ICC). Other organisations issuing standard test methods include the Association of Official Analytical Chemists (AOAC) and the American Association of Cereal Chemists (AACC).

Table 3.3. International Standard - Wheat - Specification ISO 7970: 1989

Maximum tolerances (% m/m):  
Foreign or deteriorated odour, additives, toxic substances 0
Pesticide residues, other contaminants National limit or Codex limit
Living insects 0
Moisture content 15.5*
Bulk density, minimum (kg/hl) 70
Damaged grain 15
of which:  
Broken grain 7
Shrivelled grain 8
Unsound grain 1
Grain attacked by pests 2
Other cereals 3
Extraneous matter 2
Inorganic material 0.5
Harmful and/or toxic seeds, bunted grains and ergot 0.5
Ergot 0.05
Falling number, minimum 160

'Lower moisture contents are required for certain destinations, in relation to the climate, and duration of transport and of storage. For further information, see ISO 6322, parts 1, 2 and 3.
Source: International Organisation for Standardisation


Table 3.4. Codex Standard for Maize (Corn) Codex Stan 153-1985

Maximum tolerances (% m/m):  
Abnormal or foreign odour 0
Moisture content 15.5
Blemished grain 7
of which:  
diseased grain 0.5
Broken kernels 6
Other grains 2
Foreign matter 2
of which:  
inorganic matter 0.5
Filth 0.1
Toxic or noxious seed, heavy metals, free from
microorganisms or poisonous or amounts hazardous
deleterious substances to health

Source: Codex Alimentarius Commission

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