To be U.S. Grade A, honey has to have a water content of 18.6% or less. Honey that is over 18.6% water content, will ferment over time.
There are many types of refractometers that have different scales and are used for a specific fluid in many different industries.
Beekeepers use a refractometer that is set up for honey. A honey refractometer is set up with a moisture content of 13% - 30% on the measurement scale.
Honey refractometers are electronic or a visual lens.
The electronic refractometers use a sample of honey and will give you a moisture read out.
I myself prefer the low tech lens style. A sample of honey is put on the lens. Then the sample is held up to a bright light for the reading. How the light passes through the honey sample gives the reading on the scale in the instrument. I like the low tech system because it is visual and you can see the results.
A refractometer has to be calibrated to make sure it is accurate. Calibration fluid is used to calibrate the instrument. I always calibrate my refractometer before every season to make sure it is accurate.
Beekeepers can bring me a sample of their honey and I will test it for free.
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| This is what the scale looks like in a Atago refractometer. Where the purple line and the white color meet is your number. Then a temperature adjustment is figured off the attached thermometer. This sample is reading about 19.3%. Different manufacturers may have different looking scales |
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| Atago Refractometer |