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    Home > Chemicals Industry > Chemical Technology > Determination of moisture in flour

    Determination of moisture in flour

    • Last Update: 2021-07-25
    • Source: Internet
    • Author: User
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    This training uses the direct drying method (according to the first method of the "GB5009.
    3-2010 National Food Safety Standard for the Determination of Moisture in Food")
    .

    1.
    Purpose requirements

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

    (2) Learn how to heat and dry the sample to a constant weight, and learn how to judge the constant weight
    .

    (3) Master the method and operation skills of the direct drying method to determine moisture
    .

    (4) It can truthfully record the phenomena and problems of the detection process, and analyze the source of error in the measurement process of the direct drying method
    .

    (5) The result will be calculated correctly
    .

    2.
    Principles of training

    The food samples are heated and dried in an oven under normal pressure at 101-105°C to a constant weight, and the moisture content is calculated by the difference between the masses of the samples before and after drying
    .

    3.
    Training supplies

    (1) Electronic balance
    .

    (2) Electric heating constant temperature drying oven
    .

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

    (4) Dryer (with desiccant inside)
    .

    4.
    Safety reminder

    The electric heating constant temperature drying oven must be checked for electric leakage, electric heating wire overlap or collision, etc.
    before use.
    The external power supply should be cut off after use to avoid accidents; it should not be dried, flammable, explosive, volatile, or corrosive.
    The items; when taking the baked items, use special tools or wear heat-insulating gloves to avoid burns
    .

    5.
    Operation steps

    (1) Dry the weighing bottle to a constant weight.
    Take the clean weighing bottle and mark it, place it in a drying oven at 101~105℃, and place the bottle cap on the side of the bottle.
    Cool in the desiccator for 0.
    5h and weigh
    .


    Repeat this operation until constant weight


    (2) Sample loading: Add 2.
    00 to 5.
    00g of flour sample into a weighing bottle that has a constant weight.
    The sample size should preferably not exceed 5mm in thickness
    .


    Capped and accurately weighed


    (3) The sample is dried to a constant weight.
    Place the weighing bottle mentioned above in a drying box, with the bottle cap obliquely supported on the side of the bottle to allow water to evaporate
    .


    After drying at 101~105℃ for 2~4h, cover it and take it out, put it in a desiccator and cool for 0.


    6.
    Result calculation

    (1) Data record (please design the form by yourself)
    .

    (2) Result calculation

    Where x——the moisture content in the sample, g/100g

    m 1 ——The mass of the weighing bottle, g

    m 2 ——The mass of the weighing bottle and the sample before drying, g

    m 3 ——The mass of the weighing bottle and the sample after constant weight, g

    The calculation result retains three significant figures
    .

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

    7.


    Tips

    (1) Scope of application: The direct drying method is suitable for various foods that are thermally stable within the range of 101~105℃, do not contain or slightly contain other volatile components, such as cereals and their products, aquatic products, soy products, milk products, meat and Lucai products
    .


    Not suitable for samples with moisture content less than 0.


    (2) Sampling, weighing, and taking out the weighing bottle from the drying box and putting it into the desiccator should be quick to shorten the time the sample is exposed to the air to prevent the sample from losing moisture or getting damp
    .

    (3) The sample properties are different, and the drying operation is different
    .

    For thick samples, you need to add a drying aid (refined sea sand or anhydrous sodium sulfate ), stir evenly with a small glass rod to prevent encrustation or agglomeration, and increase the evaporation area
    .


    The sea sand used should be washed with water to remove the soil, then boiled with 6mol/L hydrochloric acid for 0.


    Foods with high moisture content (above 16%) are usually measured by the secondary drying method
    .


    For bread, it should be air-dried in the air first, then ground and dried in an oven


    When the moisture content is below 14%, it is called safe moisture, that is, it is crushed and screened under laboratory conditions, and the moisture content generally does not change
    .

    (4) The selection of the operating conditions of the drying method mainly includes: the selection of sample size, weighing vessel specifications, drying equipment and drying conditions
    .


    For example, the weight of the sample is generally controlled at 1.


    (5) In actual work, if it is necessary to measure both moisture and ash, the measurement of moisture and ash is often combined to save time and energy


     

     

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