How to read a handheld refractometer for salinity

Calibrate the refractometer and accurately measure the water content of honey

Refractometers are used to measure the water content of honey, similar to how winemakers use them to determine the sugar content of the must. With the honey refractometer, a blue-white borderline on the measuring scale shows the water content in percent. According to the German honey regulation, this should be below 20 percent. Beekeepers who sell their honey in a DIB jar must ensure that the water content does not exceed 18 percent. What to do if the self-determined value does not match the measurement of the D.I.B. honey control?

Then you should first check whether the refractometer is correctly adjusted. Because regardless of the price you paid, the devices can simply be incorrectly calibrated.

Calibrate and measure the refractometer correctly

In order to measure correctly with the refractometer, you have to adjust it and thus set the scaling correctly. Two different test media are required for this:

  1. Clove oil: The refractometer is initially adjusted to 19.6 percent using clove oil and a special glass test body.
  2. Olive or sunflower oil: Depending on the measuring range of the device used, the adjustment is then checked in a second step with virgin olive oil or sunflower oil.

Both steps are carried out at a temperature of 20 degrees, regardless of whether the device is with or without temperature compensation.

The refractometer should show a value of 27.0 to 27.2 percent for olive oil and 24.8 to 25.2 percent for sunflower oil. Then the scaling of the device is OK or the slope of the scale is correct.

If the measured value for olive oil or sunflower oil deviates, there is a slope error on the measuring scale. A correction table can be created to convert the readings. It is determined in which ratio the measured value deviates from the basic adjustment of 19.6 percent. This correction value can in future be taken into account when measuring the water content.

Check the automatic temperature compensation

When the temperature rises, the refractive index changes along with the thermal expansion, and with it the measured water content of the honey. To compensate for this, many refractometers have an “automatic temperature compensation” (ATC). To check whether the automatic temperature compensation works, test a jar of liquid honey at different temperatures, such as 16, 20, 24 and 28 degrees. Honey and refractometer are stored for 24 hours at the temperature to be tested. The jar must be tightly closed between measurements so that the water content of the honey does not change. The measurement should give the same value at every temperature. If not, the temperature compensation of the refractometer is defective. Here, too, you can create a correction table and take the deviation into account in the future. The error is often around 0.1 percent per degree Celsius difference to the reference temperature of 20 degrees. Another method is to always measure the honey at an ambient temperature of 20 degrees.

Here you can find more information about adjusting and measuring to print out:

Use the refractometer properly

If the refractometer is adjusted and working correctly, it is easy to use: you spread a little liquid honey on the prism and press the flap firmly. After one to two minutes you look through the device and read the measured value on the blue-white, horizontal border line. This corresponds to the water content of the honey in percent. The value should be well below 18 percent. Then carefully clean and dry the refractometer.

Readjust the refractometer correctly

The refractometer usually comes with a bottle of clove oil and a glass test body so that the device can be readjusted. The measurement with clove oil and glass test body should give a value of 19.6 percent at 20 degrees. During the adjustment, a borderline appears in the spectral colors. Set the adjustment value 19.6 percent at the transition from blue to purple. If the value deviates, turn the small adjusting screw until 19.6 percent is displayed. After cleaning with a little water and washing-up liquid, the refractometer can be used again for the measurement.


Adjusting the refractometer in the video:

Measuring the water content in honey in the video:

cas / jfr 29.6.2019

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