A process already discovered at the end of the 19th century in which ions (Greek ion = wandering) - i.e. particles such as atoms or molecules - are exchanged between two substances with the help of so-called ion exchangers. Such ion exchangers are high-molecular substances such as silicate minerals (zeolites) or synthetically produced resins, which are able (without disintegrating) to release their own ions and absorb others in a solution. This is used, for example, for water softening by removing calcium and magnesium ions from the water and exchanging them for sodium ions (of the ion exchanger). A special form is ion exchange chromatography.
Ion exchange is used in winemaking for stabilisation (removal of tartar), for filtration, for acidification or deacidification and for the production of RCGM (rectified grape must concentrate). This is usually done in combination with osmosis (reverse osmosis). However, using this method can strongly change the taste and aroma of the wine. The process was therefore banned according to EU regulation and is only permitted in exceptional cases subject to notification and certain specifications.