Grading Of Produce

In the grain industry grading is critical. Botswana Bureau of Standards (BOBS) has set standards/specifications of quality for grain that is intended for human consumption. Grain has characteristics that determine its quality/grade of the product. In the grading system for grain meant for human consumption, only Grades 1 and 2 are acceptable. Generally the amount (in percentages) of the following factors determines whether grain is classified as Grade 1 or 2, and the specifications/standards vary as per the grain:

Moisture content

Moisture content means the amount of moisture in the grains.

Defective grains

Defective grains means grains that have been insect damaged, broken, water damaged, shrivelled and under developed, discoloured and heat damaged.

Foreign matter

Foreign matter means twigs, soil granules, dead insects, grains of other crops and seed coats. It should be noted that glass, stones, pieces of metals are not foreign matter as these materials are not allowed in grain; therefore a grain sample containing these is rejected.

Grains of another colour

Grains of another colour means grains of the same crop but with a different colour e.g. white maize having some yellow maize grains.

Poisonous weed seeds

Poisonous weed seeds are not allowed in grain as this renders the grain unsafe for human consumption. Examples of such weeds include mokhure, Johnson’s grass etc.

Live insects grains

Live insects grains should not have any live insects; presence of these renders the grain as reject.

The following tables show the specifications/standards for acceptable grades of maize, sorghum and pulses.

Maize -White

Factor Tolerance (%)
Grade 1 Grade 2
Moisture content 13 13
Defective grains 7 10
Foreign matter 0.3 0.5
Maize kernels of another colour 2 3
Pinked maize 12 12

 

Maize – Yellow

Factor Tolerance (%)
Grade 1 Grade 2
Moisture content 13 13
Defective grains 6 20
Foreign  matter 0.3 0.5
Maize kernels of another colour 2 3
Pinked maize 7 7

 

Pulses

Factor Tolerance (%)
Grade 1 Grade 2
Moisture content 12 12
Defective grains 7 10
Foreign  matter 1 1
Pulses of another colour 10 13

 

Sorghum

Factor Tolerance (%)
Grade 1 Grade 2
Moisture content 12 12
Defective grains 3.0 6.0
Foreign  matter 1.5 2.0
Sorghum of another colour 2.0 4.0
Small kernel 4.0 8.0
Sorghum of other class 2.0 4.0
Unthreshed sorghum 4.0 6.0
Total of the defects above 8.0 10.0
Weather stained sorghum 25 50

 

Tolerances for poisonous weed seeds and live insects are zero (0%).

Price Files

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Insects are often responsible for severe losses of the nutritive value in food grains. As a...