Various methods of concentrating grape must or wine by removing certain substances. In most cases this is done by reducing the pure water content. The oldest form is the drying of grapes, which was already used in ancient times. Today, this is achieved by a correspondingly late harvest and/or drying on straw mats/reeds and by hanging the grapes on racks for a longer period of time (see also Trockenbeerenauslese and Recioto). In osmosis (reverse osmosis, osmotic distillation), different molecule sizes of liquids or of substances contained therein are used.
Further possibilities of concentration are the use of different boiling or freezing points. Low pressure and low temperature evaporators are used for...