Determination of Relative Density of Milk, Liquor and Fruit Juice

This training uses the density meter method (standard GB/T5009.

1.

(1) Master the measurement principles and operating methods of various densitometers

(2) Learn how to correct the measured value to the standard temperature value

(3) Learn the densitometer inspection method of milk mixed with water

2.

Based on Archimedes buoyancy principle

3.

(1) Density meter (sugar hammer meter, alcohol meter, milk consistency meter)

(2) Measuring cylinder (250mL)

(3) Thermometer

(4) Food samples (juice, white wine, pure milk)

4.

The test bench or tabletop must be firm and level to prevent the container from tilting and affecting the test results

Prevent the alcohol meter from being too heavy and the solution density too low, causing the alcohol meter to fall to the bottom of the measuring cylinder, causing damage to the instrument

5.

(1) Familiar with different types of density meters
.

(2) Measure the relative density of milk with a milk thick meter

① Take commercially available milk, adjust the temperature at 10-20°C, mix it carefully, pour it into a 250mL dry measuring cylinder, and add to the 3/4 volume of the measuring cylinder
.
If there is foam, carefully skim it off with a filter paper strip
.

②Immerse the milk consistency meter into the sample to the equivalent of 30 on the scale, and then let it suspend naturally, avoiding contact with the inner wall of the cylinder
.
Let it stand for 2 to 3 minutes, and the eyes and the liquid level in the cylinder are viewed levelly, and the milky consistency count value is read out
.
At the same time, the thermometer is hung above the measuring cylinder, and the lower end is immersed in the milk to measure the temperature of the sample
.

③Convert to the degree at 20℃ or 15℃ according to the temperature of the milk sample and the reading of the milk consistency meter
.

(3) Measure the alcohol content of liquor with an alcohol meter

①Pour commercially available liquor into a dry 250mL graduated cylinder and add it to 3/4 of the volume of the graduated cylinder.
When the bubbles disappear, use a thermometer to measure the temperature of the sample
.

②Roughly estimate the alcohol content of the sample, select an alcohol meter with a suitable scale, wash and dry, carefully immerse it in the sample wine, wait for it to stand still, press it down slightly, wait until it rises to balance, and read the alcohol content
.

③According to the measured temperature and the reading of the alcohol meter, check the table to correct the alcohol content of 20℃
.

(4) Use a sugar hammer to measure the concentration of sucrose solution

① Pour the sucrose solution into a dry 250mL graduated cylinder and add it to 3/4 of the volume of the graduated cylinder.
When the bubbles disappear, use a thermometer to measure the temperature of the sample
.

② After washing and drying the sugar hammer, carefully immerse it in the sample solution.
After it is still, press it down slightly until it floats to balance, and then read the scale at the intersection of the liquid level and the sugar hammer
.

③Based on the temperature measured and the reading of the sugar hammer, check the table and correct it to a value of 20°C
.

6.
Result calculation

(1) Data recording According to the indication value and measured temperature of various densitometers, check Appendix IV to calibrate the density of the sample
.

(2) Determine whether the milk is mixed with water.
The relative density of normal milk is 1.
028-1.
032, and the milk density of 1.
030 is the average sum of the various components contained in it
.
The relative density of cow's milk decreases after being mixed with water.
Each addition of water equivalent to 10% of the total volume can reduce the relative density of cow's milk by 0.
003, which is 3 degrees; conversely, the relative density of skimmed cow's milk increases
.
Therefore, the densitometer method can be used to check whether the milk is mixed with water
.
This method can be tested quickly without being restricted by the environment, and the estimated water content can be calculated as follows:

Where X—estimated water content

d ₁ —The density of normal milk expressed by the degree of milk consistency (for example, the density of normal milk is 1.
029, then the degree of milk consistency is 29 degrees)

d ₂ -Density of the tested milk expressed in the degree of milk consistency.
When the water content of the milk is less than 10%, the error of the result measured by this method is relatively large
.
Milk consistency can be used not only to assess the quality of milk, but also to assess the taste of milk
.
Generally speaking, milk with higher milk consistency has a thicker mouthfeel, but on the contrary it is thinner
.

7.
Tips

(1) The densitometer method is simple and quick to measure liquid samples, but the accuracy is low, and more sample liquids are required, and it is not suitable for extremely volatile sample liquids
.

(2) Choose a density meter with an appropriate scale according to the relative density of the liquid; handle the density meter with care, and do not hold the tail in a non-vertical state or when it is inverted to avoid breaking the density meter
.

(3) The selection of the measuring cylinder should be determined according to the length of the density meter; the measuring cylinder should be placed on the surface of the water platform during operation; the density meter should be suspended in the center of the measuring cylinder without touching the wall and bottom of the vessel; there should be no air bubbles in the liquid to be tested
.

(4) Pay attention to reading in the order of the density meter (from bottom to top or top to bottom); the alcohol meter reading is based on the lower edge of the meniscus, and the degree of milk consistency is based on the upper edge of the meniscus
.