GB/T 5497-2025Inspection of grain and oils - Determination of the moisture content of grain and oilseeds (English PDF)

4.2.1 Balance. Sensitivity of

0.001 g.

4.2.2 Electric constant-temperature drying oven. 70 °C ± 2 °C, 105 °C ± 2 °C, 130 °C ± 2 °C.

4.2.3 Grinder. The grinding process is rapid and exhibits no significant heat generation, thereby preventing external air from affecting the moisture content of the specimen; the ground specimen shall meet the required particle size specifications. A disc-type moisture-preserving mill may be used, though the equipment is not limited to this type.

4.2.4 Desiccator. Containing silica gel or an equivalent effective desiccant.

4.2.5 Aluminum dish. Equipped with a tight-fitting lid; internal diameters of

15.0 cm; height between

4.2.6 Slicer or knife.

4.3 Preparation of specimens

4.3.1 Sampling and dividing are conducted in accordance with GB/T 5491; the sample dividing amount shall comply with the provisions specified in Table 1.

4.3.2 Specimens shall be prepared in accordance with the methods specified in Table 1. Immediately after preparation, the specimens shall be placed into clean, airtight containers for storage prior to use.

4.4.1.1 Place an uncovered aluminum dish with an inner diameter of

5.5 cm into an electric constant-temperature drying oven that has been pre-adjusted to 130 °C ± 2 °C to dry for 40 min, then remove the dish, place it in a desiccator to cool to room temperature, remove it and weigh (m0), to the nearest

0.001 g.

4.4.1.2 Use an aluminum dish to weigh out 2 g (using a

4.5 cm diameter aluminum dish) or 3 g (using a

5.5 cm diameter aluminum dish) of specimen (m1), to the nearest

0.001 g; spread the specimen to ensure it is distributed evenly across the bottom of the dish; for oilseeds with shells, the specimen may be weighed based on the kernel-to-shell ratio, or the kernels and shells may be weighed separately. Once the temperature of the electric constant-temperature drying oven has risen to 135 °C ~ 145 °C, invert the aluminum dish lid and place it over the bottom of the dish, place the aluminum dish containing the specimen into the electric constant-temperature drying oven, adjust the temperature of the electric constant-temperature drying oven to 130 °C ± 2 °C within 5 min, and start the timer. After drying for 40 min, remove the aluminum dish, cover it with its lid, place it in a desiccator to cool to room temperature, remove it and weigh (m2).

4.4.2.1 First drying 4.4.2.1.1 Place an aluminum dish with an inner diameter of

15.0 cm into an electric constant-temperature drying oven that has been pre-adjusted to 105 °C ± 2 °C (for grain) or 70 °C ± 2 °C (for oilseeds) to dry for 30 min ~ 40 min, then remove the dish, allow it to cool naturally to room temperature, and weigh it to the nearest

0.001 g. 4.4.2.1.2 Weigh out a clean, whole-grain specimen of 30 g ~ 100 g (m3), to the nearest

0.001 g, and place it into the aluminum dish. Spread the specimen so that it is distributed uniformly across the bottom of the dish, place the dish in an electric constant- temperature drying oven that has been pre-adjusted to 105 °C ± 2 °C (for grain) or 70 °C ± 2 °C (for oilseeds), and dry for 30 min to 40 min. If necessary, the drying time may be extended to ensure that the grain is dried to a moisture content not exceeding 18.0 %, and the oilseeds is dried to a moisture content not exceeding 13.0 %. Remove the dish, allow it to cool naturally to room temperature, cool for at least 2 h, then weigh it. Subtract the mass of the aluminum dish to obtain the mass of the specimen after the first drying (m4).

4.4.2.2 Second drying Immediately take the specimen dried in accordance with

4.4.2.1 and prepare it according to the preparation methods specified in Table 1; then, subject the prepared specimen to a second drying in accordance with 4.4.1.

4.5 Calculation and expression of results

4.5.1 The moisture content of grain and oilseeds determined by single drying method is calculated according to formula (1). where. w - the moisture content of the specimen, %; m0 - the mass of the aluminum dish, in grams (g); m1 - the mass of the specimen and aluminum dish before drying, in grams (g); m2 - the mass of the specimen and aluminum dish after drying, in grams (g).

4.5.2 The moisture content of shelled oilseeds, where the moisture of the kernel and shell are determined separately, is calculated according to formula (2). where. w - the moisture content of the specimen, %; w1 - the moisture content of the kernel, %; w2 - the moisture content of the shell, %; A - the total kernel percentage, %.

4.5.3 The moisture content of grain and oilseeds determined by twice drying method is calculated according to formula (3). where. w - the moisture content of the specimen, %; m3 - the mass of the specimen before the first drying, in grams (g); m4 - the mass of the specimen after the first drying, in grams (g); m5 - the mass of the specimen before the second drying, in grams (g); m6 - the mass of the specimen after the second drying, in grams (g).

4.5.4 Under repeatability conditions, the average value of the two independent test results obtained constitutes the determination result; the determination result is rounded to one decimal place.

4.6 Precision

4.6.1 Inter-laboratory tests The inter-laboratory test results regarding the precision of this method are presented in Annex A.

4.6.2 Repeatability The absolute difference between two independent test results obtained in the same laboratory, by the same operator, using the same equipment, and following the same test method, with tests performed independently on the same test object within a short interval of time, shall not exceed 0.2 %.

4.6.3 Reproducibility The absolute difference between two independent test results obtained in different laboratories, by different operators, using different equipment, and following the same test method, with tests performed independently on the same test object, shall not exceed 0.5 %.

5.2 Instruments and equipment

5.2.1 Waterlogging suspend moisture meter (moisture meter). Shall comply with the requirements specified in LS/T 3705.

5.2.2 Sample weighing vessel. Open on one side, capable of holding approximately 10 g of specimen.

5.2.3 Stirring rod. Made of stainless steel, 2 mm in diameter, and 85 mm in length.

5.2.4 Water injector. A 20 mL medical syringe.

5.2.5 Mortar. Capable of holding approximately 100 g of specimen.

5.2.6 Electric hammer mill. Equipped with round-hole sieves having diameters of

2.5 mm; during operation, the temperature of the mill shall not exceed 25 °C.