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 this purpose. This concentrates the sugar, but also removes volatile flavours. An improved technique is vacuum concentration, because water evaporates at lower air pressure at already 30 °C (and less), which is not much higher than a conventional fermentation temperature. As a result, considerably less flavourings are lost. A relatively new process is Spinning Cone Column. These techniques are used in the production of RTK, among other things.
The freeze concentration (French: cryoextraction) mimics the natural processes involved in the production of ice wine. The whole grapes are frozen to minus 6 °C. First the water part freezes and leaves the remaining components in concentrated form. Then the grapes are pressed, whereby only the highly concentrated, sugar-rich extract is drained off. However, the quality of genuine ice wines is not achieved and this technique (used mainly in the New World and the French Sauternes area) is not without controversy.
In any case, must concentration is considered one of the many forms of enrichment (alcohol increase) and is subject to the relevant regulations. Under the heading of enrichment, the EU wine legislation is listed. The topic of concentration became the focus of interest as a result of the wine trade agreement between the USA and the European Union signed at the end of 2005.
Another method that can be described as concentration is the method used for the first time in France (Bordeaux, Burgundy), known as saignée (bleeding), in which a certain proportion of the grape must is drawn off during maceration and this part is produced as light rosé and the other part as red wine rich in extract. Similarly colourless wines are the wine types Weißherbst (Germany), Gleichgepresßter (Austria) and Süßdruck (Switzerland). The remaining part of the must thus results in red wines rich in colour and extract.
Complete lists of the numerous vinification measures and cellar techniques, as well as the various types of wine, sparkling wine and distillate regulated by wine law are contained under the keyword vinification. Comprehensive information on wine law can be found under the keyword wine law.