Various methods of concentrating grape must or wine by removing certain substances and/or 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 late harvesting and/or drying on straw mats/reeds and hanging the grapes on racks for longer periods (see Trockenbeerenauslese and Recioto). Osmosis (reverse osmosis, osmotic distillation) utilises different molecular sizes of liquids or the substances they contain.
Other possibilities for concentration are the utilisation of different boiling or freezing points. Low-pressure and low-temperature evaporators are used for this. This concentrates the sugar, but also removes volatile flavours. An improved technique is vacuum concentration, as water evaporates at low air pressure at just 30 °C (and below), which is not much higher than a conventional fermentation temperature. This means that far fewer flavours are lost. A relatively new process is the spinning cone column. These techniques are used in the production of RCGM (rectified grape must concentrate), among other things.
Freeze concentration (cryoextraction) mimics the natural processes involved in the production of ice wine. The whole grapes are frozen to minus 6 °C. The water content freezes first, leaving the remaining components in concentrated form. The grapes are then pressed, leaving only the highly concentrated, sugar-rich extract. However, the quality of real ice wines is not achieved and this technique (which is mainly used in the New World and in the French Sauternes region) is not without controversy.
Must concentration is definitely one of the many forms of enrichment (alcohol increase) and is subject to the relevant regulations. The EU wine regulations are listed under the keyword " enrichment". The issue of concentration became the centre of attention as a result of the wine trade agreement signed between the USA and the European Union at the end of 2005.
The method known as saignée (bleeding), which was first used in France (Bordeaux, Burgundy), can also be described as concentration, whereby a certain proportion of the grape must is drawn off during mash fermentation and this part is produced as a light-coloured rosé and the other part as an extract-rich red wine. Similar wines with a weak colour are the Weißherbst (Germany), Gleichgepreßter (Austria) and Süßdruck (Switzerland) wine types. The remaining must content results in red wines that are correspondingly richer in colour and extract.
For the production of alcoholic beverages, see Champagne (sparkling wines), distillation (distillates), spirits (types), winemaking (wines and wine types) and wine law (wine law issues).
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