Refractometry is the measurement of refractive index using one of several types of refractometer. It is a fast, non-destructive technique widely used in food quality control: determining the soluble-solids content of fruit juices, jams, and syrups, usually read as degrees Brix; checking honey concentration and detecting added water; and confirming the purity of fats, oils, and essential oils. Because only a drop of sample is needed and the reading takes seconds, refractometry suits both laboratory analysis and rapid checks on the production line.