A process discovered as early as the end of the 19th century in which ions (grch. ion = migrating) - i.e. particles such as atoms or molecules - are exchanged between two substances with the aid of so-called ion exchangers. Such ion exchangers are high-molecular substances such as silicate minerals (zeolites) or synthetically produced resins, which (without decomposing) are able to release their own ions and absorb others in a solution. This serves for example for water softening by removing calcium and magnesium ions from the water and exchanging them for sodium ions (from the ion exchanger). A special form is ion exchange chromatography.
Ion exchange is used in winemaking for stabilisation (removal of tartar), filtration, acidification or deacidification and for the production of RTK (rectified grape must concentrate). This is usually practised in combination with osmosis (reverse osmosis). The use of osmosis can, however, significantly alter the taste or aroma of the wine. The process has therefore been banned in accordance with EU regulations and is only permitted in exceptional cases subject to notification and with certain specifications.