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QUALITY CONTROL LABORATORY |
Standard Operating Procedure |
Doc ID: SOP-QC-GRAIN-001 Version: 2.0 |
| Gravimetric Determination of Foreign Matter in Food Grains & Pulses |
Effective Date: July 2026 Page: 1 of 1 |
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1. Purpose & Scope
This procedure defines the standardized gravimetric method for identifying, separating, and quantifying foreign matter in whole, unprocessed, decorticated (de-husked), or split cereal grains, millets, seeds, and pulses.
1.1 Scope of Commodities
| Category | Applicable Commodities |
|---|---|
| Cereal Grains, Millets & Seeds | Wheat, Corn (Maize), Sorghum, Oats, Finger Millet, Pearl Millet (whole/decorticated), Rice, Basmati Rice, Chia Seeds, Triticale. |
| Pulses & Legumes (Whole, De-husked, or Split) |
Lentil, Black Gram, Mung Bean, Chickpea (including green chickpea), Horse Gram, Common Bean / Field Bean, Dry Pea, Soybean, Kidney Bean / Broad Bean / Black Bean, Cowpea (Black-eyed Pea), Moth Bean. |
2. Definitions
Foreign Matter refers to any extraneous material present in the sample other than the designated food grain. It is categorized as follows:
- Inorganic Matter: Metallic pieces, sand, gravel, dirt, pebbles, stones, soil lumps, clay, mud, animal waste, and adhering mud on grain surfaces (e.g., rice).
- Organic Matter: Husks, stalks, straw, weed seeds, inedible non-target grains, and unhusked rice (paddy) present within processed rice.
3. Apparatus & Equipment
- a) Analytical Balance: Precision/sensitivity of
0.001 g. - b) Test Sieves: Standard round-hole laboratory sieves:
- Top Sieve: 4.00 mm aperture
- Second Sieve: 3.35 mm aperture
- Third Sieve: 1.70 mm aperture
- Fourth Sieve: 1.00 mm aperture
- c) Bottom Receiver Pan: Solid non-perforated collection pan.
- d) Trays: Flat enamel trays (approx. 30 cm diameter with raised rims).
- e) Scoop: Small sampling scoop.
- f) Forceps: Precision laboratory forceps.
- g) Magnifying Glass: Handheld magnifier (approx. 7.5 cm diameter, 10× magnification).
4. Analytical Procedure
- Sample Preparation: Homogenize and reduce the laboratory sample using the conical divider or quartering method to obtain a representative test portion.
- Weigh 500 g for standard grains, pulses, and large legumes.
- Weigh 250 g for rice, millets, and small-sized seeds.
- Sieve Nest Assembly: Nest the test sieves in descending order of aperture size, stacking them top-to-bottom over the bottom receiver pan:
- Top Sieve: 4.00 mm aperture
- Second Sieve: 3.35 mm aperture
- Third Sieve: 1.70 mm aperture
- Bottom Sieve: 1.00 mm aperture
- Bottom Pan: Solid receiver pan (at the very bottom)
- Fractionation: Transfer the weighed sample into the top sieve (4.00 mm). Agitate/shake the nested sieve stack horizontally for 2 to 3 minutes to achieve complete mechanical separation.
- Sorting & Extraction:
- Separate the nested sieves carefully.
- Empty the contents of each sieve level onto an enamel tray.
- Using a 10× magnifying glass and forceps, manually pick out all organic and inorganic extraneous matter from each sieve.
- Consolidation & Final Mass:
- Collect all fine mineral dust, sand, and dirt gathered in the solid bottom receiver pan.
- Combine all extracted organic and inorganic extraneous matter from all sieve levels and the bottom pan.
- Weigh the total consolidated extraneous matter on the analytical balance to the nearest
0.001 g(WExtraneous).
5. Calculation and Units of Expression
Calculate the percentage of foreign matter present in the sample using the following equation:
Foreign matter (%) =
Mass of extraneous matter
Mass of sample
× 100
6. On-Demand Analysis Calculator
Foreign Matter: 0.000 %
7. Reference
- AOAC 17th Edn, 2000: Official Method 970.66 – Light and Heavy Filth.
- IS 4333 (Part 1): 1996: Methods of Analysis for Food Grains – Part 1: Refractions.
- IS 460 (Part 1): 1985: Specification for Test Sieves (Wire Cloth Test Sieves).
- FSSAI Manual of Methods of Analysis of Foods: Cereal and Cereal Products.