Abstract: An alcoholic liquid obtained by fermenting a must or a wort is initially subjected to ultrafiltration or to reverse osmosis to obtain a permeate which contains a higher proportion of water and alcohol than the starting liquid and a concentrate which contains a higher proportion of the substances that flavor the starting liquid. The permeate is then subjected to reverse osmosis using a membrane which is substantially impermeable to alcohol, while still being permeable to water. The concentrate from the second step is added to the concentrate from the first step to produce a liquid which has a higher concentration of alcohol than the starting liquid. The resulting liquid may be useable at said higher concentration as a beverage, or it may be used for transport and/or for storage, with water being added to thereto to restore the beverage substantially to its starting condition before being drunk.