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Vacuum rectification

See under alcohol reduction.

A reduction of alcohol in wine can be achieved by means of various physical and/or chemical processes. Especially in southern regions this is a relatively common practice with the aim of producing aromatic and less alcohol-rich wines. The simplest and cheapest form is the addition of fruit juice or grape juice, which is used in the production of coolers, or of water (stretching). A certain alcohol content can also be obtained by stopping the fermentation by means of cooling, which is mainly practiced in Italy for simple wines. The result is sweet, sparkling and low-alcohol wines. Mostly thermal separation processes such as vacuum distillation (vacuum rectification) are used.

The boiling point of pure ethanol is about 78 °Celsius, which is used in distillation. However, this temperature would be too high for the purpose of alcohol reduction, as valuable aromatic substances would be lost. This is why this is done at a reduced pressure of 0.07 to 0.15 bar (otherwise 1 bar) in the temperature range of 30 to 60 °Celsius in order to keep any material changes to a minimum. The dwell time and temperature should be as low as possible. Other processes include electrodialysis, high-pressure extraction, filtration (nanofiltration, ultrafiltration), osmosis (reverse osmosis, osmotic distillation), pervaporation and spinning cone column. The specifications regarding the permitted processes vary from country to country. In Austria, the relevant provision...

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