A refractometer is used to test sugar concentrations in a solution. When light passes through a liquid it bends at an angle. Depending on the density of the liquid, this angle becomes more or less pronounced. Refractometers work using this property and translate this shifted angle of refracted light to fall on a graduated Brix chart that is viewable in the eyepiece.
Using a Refractometer:
To run the test with a manual model, add a few drops of sample to the lense, close the cover and hold the refractometer up to a light source. Next look into the eyepiece and reference the transition line where the blue and white fields meet: where they intersect on the chart is the Brix reading. To run the test with a digital refractometer, simple add 3 drops of sample to the lense and push the button. Seconds later the results will be automatically displayed.
Note: A refractometer cannot be directly used after fermentation has taken place as alcohol distorts the reading. However, a conversion calculator (MS Excel based) is available from MoreWine! on request. Important: you must have an accurate starting Brix number for this to work!