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Determination of moisture in flour

2023-12-22 13:59

1. Purpose requirements

(1) Further proficient in balance weighing operations, able to use electric heating drying boxes and dryers correctly.

(2) Learn the operation of heating and drying the sample to a constant weight, and learn the method of judging the constant weight.

(3) Master the method and operational skills of direct drying method for determining moisture content.

(4) Be able to truthfully record the phenomena and problems during the testing process, and analyze the sources of errors in the direct drying method measurement process.

(5) I will calculate the results correctly.

2. Principles of Practical Training

Heat and dry food samples in an oven at atmospheric pressure and 101-105 ℃ to a constant weight, and calculate the moisture content by comparing the mass difference of the samples before and after drying.

3. Training supplies

(1) Electronic balance.

(2) Electric constant temperature drying oven.

(3) Glass flat weighing bottle (inner diameter 60-70mm, height below 35mm).

(4) Drier (with desiccant inside).

4. Safety Reminder

Before using the electric constant temperature drying oven, it is necessary to check for any leakage, overlapping or collision of the heating wires. After use, the external power supply should be cut off to avoid accidents; Do not dry flammable, explosive, volatile, or corrosive materials; When taking items for baking and melting, use specialized tools or wear insulated gloves to avoid burns.

5. Operation steps

(1) Dry the weighing bottle until it reaches a constant weight. Take a clean weighing bottle and label it with a number. Place it in a drying oven at 101-105 ℃, with the bottle cap diagonally supported at the edge of the bottle. Heat it for 0.5-1.0 hours, remove the cap, cool it in a dryer for 0.5 hours, and weigh it. Repeat this operation until constant weight is achieved.

(2) Sample loading: Add 2.00-5.00g of flour sample into a constant weight weighing bottle, and the appropriate amount of sample should not exceed 5mm in thickness. Cover and weigh accurately.

(3) Dry the sample to a constant weight and place the weighing bottle in a drying oven, with the bottle cap slanted on the edge of the bottle to facilitate the evaporation of water. After drying at 101-105 ℃ for 2-4 hours, cover it and take it out. Cool it in a dryer for 0.5 hours before weighing. Then place it in a drying oven at 101-105 ℃ for about 1 hour, take it out, cool it in a dryer for 0.5 hours, and weigh it again. If the difference in mass between the two times does not exceed 2mg, it is considered constant weight.

6. Result calculation

(1) Data recording (please design your own table).

(2) Result calculation

In the formula, x represents the moisture content in the sample, g/100g

M1- Mass of weighing bottle, g

M2- Mass of weighing bottle and sample before drying, g

M3- Mass of weighing bottle and sample after constant weight, g

Keep three significant digits in the calculation result.

The absolute difference between two independent measurement results obtained under repetitive conditions shall not exceed 5% of the arithmetic mean.

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