refractometer, an instrument for measuring a refractive index, which is related to the amount by which the angle of a light wave is changed when passing through the boundary between two media. The amount of refraction is a convenient way to measure solute concentration of a solution and is widely used in viticulture and winemaking to follow the ripeness of grapes (by measuring must weight) and changes during vinification. Refractometers may be precision laboratory instruments or pocket versions that can be used in the vineyard. In either case, temperature correction or control is important for accuracy.
