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    Home > Chemicals Industry > Chemical Technology > Determination of other physical properties of food (1)

    Determination of other physical properties of food (1)

    • Last Update: 2021-07-25
    • Source: Internet
    • Author: User
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    1.
    Determination of beer color

    The color of beer directly affects its quality and sales in the market, so it is an important indicator of beer quality
    .
    The main methods for determining the color of beer are: iodine solution visual colorimetric method, EBC colorimeter method, spectrophotometer method and LASA colorimeter method

    .
    Among them, the iodine solution visual colorimetric method is a traditional method for the determination of beer color.
    This method was widely used by beer production enterprises before the appearance of special color measurement instruments.
    However, with the development and introduction of special chroma instruments, the iodine solution The colorimetric method is gradually replaced by instrumental measurement methods

    .
    This determination adopts the EBC colorimeter method, which is the current national standard method for the determination of beer color

    .

    (1) Principle The European Beer Association (EBC) has determined the colorimetric standard with the colored glass series, and its chromaticity ranges from 2.
    0 to 27.
    0 EBC units

    .
    Inject the sample into a colorimetric device, and compare it with a set of standard colored glass under the reflected light of a fixed intensity light source.
    The standard colored glass of the same color when the sample is loaded in a 25mm cuvette is used to determine the sample's Chroma

    .

    (2) The reagent is the same as the reference solution
    .

    (3) Instrument EBC colorimeter
    .

    (4) Operation steps

    ①Sample processing: Take the beer that has been cooled in the refrigerator at 10~15℃, uncover it and filter it into a Erlenmeyer flask with quick filter paper, shake it a little, and let it stand still to fully remove the carbon dioxide in the wine
    .

    ②Preservation of the sample: Cover the degassed beer with a surface glass and keep its temperature at 15-20℃ for later use
    .

    ③ Chromaticity measurement: calibrate the instrument first, then pour the sample into a colorimetric device for color comparison and reading
    .

    (5) Result calculation

    (6) Tips

    ① The chromaticity of general light beer is 5.
    0~14.
    0EBC, and the chromaticity of dark beer and black beer is 15.
    0~40.
    0EBC

    .
    Therefore, it is necessary to dilute to the appropriate color range (2.
    0~27.
    0EBC) for the determination of strong color and black beer, and multiply the determination result by the dilution factor

    .
    The result should be expressed to two significant digits

    .

    ② The color code should be checked regularly with Hartung's solution
    .

    ③The operator's ability to observe colors and the degree of sensitivity to colors are different, so there must be certain measurement errors
    .

    ④ When the difference between the two measured values ​​of the same sample is 2-10EBC, it shall not be greater than 0.
    5EBC; when the chromaticity is greater than 10EBC, the difference between the parallel test measured values ​​of the diluted sample shall not be greater than 1EBC

    .

    ⑤Characteristics of the method: The method adopts the internationally-used EBC color scale, which eliminates tedious conversion, short measurement time, simple instrument operation, easy observation, and convenient reading
    .

    2.
    Measurement of turbidity of tap water

    Commonly used measurement methods are spectrophotometer, visual colorimetry, and turbidimeter
    .
    The following describes the visual colorimetry

    .

    (1) Principle The turbidity of the water sample is determined by comparing the water sample with a turbidity standard solution prepared from diatomaceous earth (or kaolin)
    .
    China stipulates that the turbidity produced by 1 mg of diatomaceous earth (white clay) with a certain particle size in 1 liter of water is called 1 degree

    .

    (2) Standard solution with reagent turbidity of 100 degrees
    .

    (3) Instruments

    ①100mL colorimetric tube with stopper
    .

    ②250mL colorless glass bottle with stopper
    .

    (4) Operation steps

    ①Pick up the standard solution 0, 1.
    0, 2.
    0, 3.
    0, 4.
    0, 5.
    0, 6.
    0, 7.
    0, 8.
    0, 9.
    0 and 10.
    0 mL of 100-degree turbidity standard solution in a 100 mL colorimetric tube, dilute with water to the mark, and mix

    .
    The turbidity is 0, 1.
    0, 2.
    0, 3.
    0, 4.
    0, 5.
    0, 6.
    0, 7.
    0, 8.
    0, 9.
    0, 10.
    0 degree standard solution

    .

    ②Take 100mL shaking water sample and place it in a 100mL colorimetric tube, and compare with the turbidity standard solution
    .
    It can be viewed vertically from top to bottom on the black board

    .

    (5) Measurement results

    Tap water turbidity = standard liquid turbidity similar to the turbidity of the water sample

    (6) Tips

    ① All utensils in contact with water samples must be cleaned
    .

    ②Attention should be paid to prevent the growth of fungi during the measurement, and inhibitors such as mercury chloride can be added
    .

    ③Water samples with a turbidity higher than 10 degrees should use a standard solution with a turbidity of 250 degrees
    .

     

     

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