Check out the new, mobile-friendly WineSpectator.com!
Hello there! I'm Dr. Vinifera, or "Vinny" for short. Ask me your toughest wine questions, from the technical aspects of winemaking to the fine points of etiquette. I hope you find my answers educational and even amusing. Looking for a particular answer? Check my archive and my FAQs. You can also follow me on Twitter: @AskDrVinny.
Dear Dr. Vinny,
How does reverse osmosis assist in reducing high alcohol levels?
—Catherine, Cape Town, South Africa
Some winemakers like the flavors obtained from extremely ripe grapes, but not the extra alcohol that results from the high sugar levels in the fruit. Reverse osmosis (or RO for short) is one technique they can use to reduce the alcohol without changing the fruit flavors and other elements in the wine.
In RO, wine passes through a filter—a really, really tight filter. Water and ethanol are the smallest molecules in wine, so they pass through the filter most easily. Some forms of acid also pass through, but most elements—including color, tannin and, basically, flavor—do not. (These elements are saved for later use.)
Then the colorless and tasteless water and alcohol mixture is distilled to separate the alcohol from the water. The water is then recombined with the color, flavor and tannins. Result: a small batch of wine with reduced alcohol.
This small batch is then blended back into the rest of the wine, thereby diluting the alcohol without losing any of the flavor elements (and only a tiny percentage of the volume).
RO is used in other applications, most commonly in household water purification systems. Some maple syrup producers also use RO to remove water from sap before boiling it down to syrup.
Do you have a question for Dr. Vinny? Ask it here...
Learn to taste wine like a pro, pull a cork with flair, get great wine service in a restaurant and more
Learn from the experts and get the most out of each sip. Take one of our online courses or take them all—from the ABCs of Tasting to in-depth seminars on Food Pairing, California Cabernet, Bordeaux, Tuscany, Sensory Evaluation and more.
Passionate about wine? Wine Spectator magazine is looking for an enthusiastic copy editor in the New York office.
Sips & Tips | Wine & Healthy Living
Video Theater | Collecting & Auctions
New! Ratings Flash | New! Unfiltered