Sugar/Brix Refractometer 28-62%Use this refractometer to test solutions with a higher sugar content, such as fruit juice concentrates, canned fruits containing added sugar, or ketchup as well as for egg yolk. Place a drop or two of a sample on the prism and read the results. Sper Scientific portable refractometers work in ambient light with no battery or other power source necessary. A refractometer measures the extent to which light is bent (refracted) through a liquid sample.