Refractometry is a technic which aims to determine the real part of the refractive index of a material.
A refractometer is a device that takes a measurement of the refractive index of the sample.
After calibration, the refractometer makes it possible to know the concentration of a solute in a known solvent. This is the case for determining the sugar in grape juice for example, but also the water content in a solution.
Honey must be harvested with a limit of water, otherwise this honey will ferment, and be at best unpleasant to consume or even unsuitable for sale. European legislation sets the water limit in honey at 20%. In practice we try not to harvest honeys that do not exceed 18% in the supers. Honey is hygroscopic (it absorbs water), so a safety margin is needed. Note that above 55% humidity in the ambient air, honey can never fall below 18%!
Even capped honey can have a high humidity level, so this rate must be measured to ensure that our honey meets the conditions set above. If this was not the case, you will either have to wait for it to dry naturally (pay attention to the humidity of the ambient air ) Or store the sealed supers in a dry or heated room until the correct value is obtained. .
Commercial refractometers are usually delivered calibrated and sometimes with a solution for calibration. Mine seemed to give me abnormal values, which was found to be correct after comparing it to an identical model. So I decided to calibrate it, but no calibration fluid had come with it.
So I looked for a method applicable by an amateur and found the solution below:
- Take the most accurate scale possible with zeroing (tare)
- Take a sealed container with its lid (jar of honey for example)
- Put the container on the scale and tare at 0
- Pour 66 g of sugar into the pot as precisely as possible
- Make up to 100 g with water, or better still, distilled water. This gives a 66% sugar solution.
- Close the container with its lid (which prevents water from evaporating)
- Put in a water bath at 66-70 ° C for 10-15 minutes and stir the pot regularly until the sugar is completely dissolved.
- Let cool to room temperature
- Take a drop of the solution (stir before taking it) and measure with the refractometer
- You should read 66 on the BRIX scale.
- Calibrate if necessary using the small adjustment screw on the top of the device.
In the meantime, I read somewhere that a quality extra olive oil has a refractive index that reads exactly 27% humidity or 71 ° BRIX. Oil and water do not mix, we do not measure the humidity but a refractive index which is that characteristic of olive oil. As this oil has only a very small proportion of water, the measurement is stable. I tested on several different organic extra cold pressed oils and I have 27%. WARNING, this measurement is only valid at 20 ° C and the oil and the refractometer must be at this temperature, otherwise a correction must be applied according to the temperature.
If the refractometer has automatic temperature compensation, often referred to as ATC, this correction should not be necessary.
What is important is that the product to be measured and the measuring device are at the same temperature!