Optical measuring device (refractive index meter) with which the concentration of liquids or solid bodies can be determined by refraction. A variant of such a device was developed by the German physicist Ernst Abbe (1840-1905), who was director of the observatory in Jena and owner of the company Zeiss. In viticulture can thereby the sugar content in the form of Most weight and thus potential alcohol content already in the grapes in the vineyard or in the grape be determined. In a drop of grape must enclosed between two prisms, the light is diffracted according to the sugar content and the value is usually in several common units of measurement (for example Brix. KMW. Oechsle ) are displayed on a scale.
The more concentrated the sugar solution, the more the light is broken. Thus, the degree of maturity is determined, which (among other things) as a decision-making aid for the ideal time of the so-called physiological maturity in the vintage serves. In order to obtain a representative value, at least 100 berries must be taken from different zones of the grapes and necessarily also from several grapes from different vineyard locations. These berries are crushed together in a container and then taken some juice for the measurement. Several measurements on different days in a row show the must weight development. For other measuring methods or measuring instruments see under analytical test,