Abbreviation for rectified grape must concentrate. Rectification is a thermal separation process for separating a homogeneous solution of two or more substances by repeated distillation or countercurrent distillation. This results in a concentration of all soluble substances. The result is a product without the caramel taste that is produced by heating in other processes. It is produced by partial dehydration using various methods. This is also the difference to concentrated grape must. It is usually produced by vacuum evaporation of grape must at very low temperatures to prevent the undesirable caramel taste (therefore, fire heat is obsolete). The production by means of the chemical process ion exchange is subject to strict EU regulation guidelines. A relatively new process is Spinning Cone Column, but it is not permitted within the EU. However, wines from the USA treated in this way may be marketed in the EU.
The guidelines include, among other things: pH value maximum 5, sulphur dioxide maximum 25 mg/kg, alcohol content maximum 1% vol. and sugar content not below 61.7% as measured by refractometer at 20 °C. The concentrate now has only about one fifth of its original volume. In Austria and Germany, RTK is used to enrich (increase the alcohol content) quality wines, but this is not permitted for Prädikatswein (in Austria from Kabinett). As a sweetening agent, RTK is only permitted in Austria for simple wine (table wine) and country wine(wine PGI), in Germany as a so-called sweet reserve also for quality wine but not for Prädikatswein. In colder wine-growing regions, RTK is also used for blending simple, acid-stressed wines in order to make them sweeter and milder. In England, it is also common practice to make a wine called British Wine (also Made Wine) from it (i.e. without grapes). The world's largest producer of RTK is South Africa. In Europe, large quantities are produced in Italy, France and Spain.
A complete list of the numerous vinification measures and cellar techniques, as well as the types of wine, sparkling wine and distillate regulated by wine law, can be found under the keyword vinification. Comprehensive information on wine law can be found under the keyword wine law.