Technical Note #2: Managing Alcohol in Wine
Alcohol in Wine Today
The problem of alcohol in wine is just the opposite of what it was just a few decades ago. Over much of wine’s history, the problem has been grapes not getting ripe enough and alcohol levels being too low. Thus, many European regulations tie designations of wine quality to minimum degrees of alcohol. For example, to be designated as “reserve”, a Rioja must have a higher level of alcohol than the simpler “crianza”, and a Valpolicella Superiore must have higher alcohol than a regular Valpolicella.
Today, with climate change creating warmer temperatures and higher sugar potential in grapes the problem is too much alcohol. The average alcohol for Napa Valley Cabernet 30 years ago was in the mid-12% range. Today it is well over 14%, and today’s Napa Valley Cabernet is completely different from before. In Germany even 20 years ago, climate rarely allowed for grapes to reach maturity levels that would support a balanced dry Riesling of 12-13%. Today, most of the Riesling consumed in Germany is dry with alcohol levels closer to 13% than 10% due to warmer conditions overall.
In this technical note we examine the strategies and techniques used by winemakers in the vineyard and the winery to reduce excessive alcohol levels in wine. In excess, alcohol destroys the more delicate aromas and flavors in wine and undermines elegance and balance.
Today’s attempts to reduce alcohol in wine, and the controversy around some of the techniques, should be seen in context. Winemakers have long manipulated alcohol levels to achieve a particular, consistent style. Chaptalization—adding sugar to wine to increase alcohol levels—has been employed in Europe for centuries, resulting at times in violent protests1. Winemakers may also add alcohol to yield a strong, age-worthy wine. Port producers, for example, fortify red wine with brandy to raise alcohol, retain residual sugar, and yield a robust, long-lived wine. Conversely, Champagne producers purposely pick grapes with lower sugar (and potential alcohol) so that when the wine produced from them is put through secondary fermentation in the bottle, the increase in alcohol will not be so high as to make an inelegant, unbalanced sparkling wine.
Reducing Alcohol Levels
Today’s winemaking toolkit allows a producer to control alcohol by using traditional means such as picking the grapes earlier with lower sugar levels or blending less strong wines with richer ones, or by employing highly technical and sophisticated means such as reverse osmosis.
In the Vineyard
To control excessive alcohol potential in warmer areas and with global warming issues, alcohol management begins in the vineyard. Leaving a larger crop on the vine can slow down ripening, thus producing lower sugar in the grapes. Or, as has been shown at some properties in Napa [Dominus comes to mind], by decreasing the height of the canopy (and therefore fewer leaves), potential alcohol level was reduced by up to .75% in the wine. Viticultural techniques to slow vines down such as less vigorous rootstocks, later ripening clones, or a move to cooler areas, are key propositions for managing alcohol in today’s climate.
In the Winery
Winemakers also have options for reducing alcohol in the winery. The simplest, if illegal in some places (not in California), is to dilute the must with water (Jesus juice). This works of course, but it also dilutes fruit extract and changes the acid balance in the wine. Blending less alcoholic wine into one more so is also a time-honored tradition; no need for fancy equipment! Blending is an extremely important tool, particularly for wineries that bottle large volume cuvées, where the penalty for high alcohol is very large. One example serves to demonstrate. Columbia Crest may bottle 200,000 cases of Grand Reserve Cabernet in a given vintage. If the wine’s blend remains below 14%, the approximate federal tax is about $578,000; if it is over 14% that figure rises to $780,000 plus!
Yet today’s wine market still has a “jones” for rich, fleshy, ripe and fruity wines. Getting those flavors in warmer areas like Napa Valley generally requires later harvesting, waiting for the phenolic maturation to catch up to more rapid sugar accumulation and high alcohols. In cooler places or vintages producers, as in Bordeaux for example, have a different problem; their wines need concentration due to lack of sufficient sugar/alcohol in the wine to balance. What’s a winemaker to do? Enter the machine--spinning cones, reverse osmosis, cross-flow filtration, and who knows what’s next!
Spinning Cones. The Spinning Cone Column was developed in Australia by ConeTech. It consists of a vertical stainless steel cylinder that uses centrifugal force and vacuum to remove alcohol. Wine is fed into the top of the column and works its way down through a series of inverted cones, converting volatiles into a vapor stream, which is then condensed in a concentrated liquid form. This is followed by a second, higher temperature pass of the liquid through the cones to extract up to 1-2% alcohol.
Reverse Osmosis. Reverse osmosis machines have been used in Bordeaux for at least four decades – larger chateaux like Leoville Las Cases used them for years to concentrate dilute musts by removing a percentage of water, concentrating the remaining juice. [However, with today’s warmer temperatures, the Chateau no longer needs to employ it.] Removing alcohol in a percentage of blend (often no more than 10% of the total amount of juice) and blending back in the low or no alcohol permeate to the whole, may be all that is necessary to make a balanced wine that is more expressive and harmonious2.
Cross-Flow Filtration. This is a type of filtration, developed by MIT in the 1960s, in which the liquid passes tangentially across the surface of the filter rather than into the filter. Wineries began using this technology in the 1980s but encountered a number of difficulties. However, in recent years the development of new filter membranes has made cross-flow filtration superior to direct filtration3. Cross-flow filtration can address numerous problems, including alcohol adjustment. The development of new, mobile filtration systems have reduced the costs of cross-filtration to small wine producers and increased its use.
While complicated, compared to adding water, the new technologies have less negative effect on the finished wine. They are not adding water, the level of volatiles (flavor/aroma carrying) removed is lower (in Memstar’s reverse osmosis), and no high level of heat is needed to perform the functions. Back-blending the de-alcoholised permeate lowers the overall alcohol level to the desired level in an efficient, precise manner. As Clark Smith notes in his book Postmodern Winemaking, alcohol reduction techniques are used in California by up to 40% of all producers. Reverse osmosis and spinning cones are legal (within a stipulated limit) in the European Union and increasingly common, especially in Italy’s Piedmont and Tuscany regions4.
New Yeast Strains. In addition to these physical manipulations, there is the tantalizing possibility of new yeast strains that are less efficient in converting sugars to alcohol. Australian researchers at the Australian Wine Research Institute have identified a yeast strain, Metschnikowia Pulcherrima (AWRI 1149) that reduces alcohol levels by as much as 1.4%. In addition, there are genetically modified yeast strains that also reduce alcohol levels and one day may be used in making wine, if consumers become more accepting of genetically modified foods.
Good or Bad?
As with new technology more generally, the introduction of new practices to reduce alcohol in wine are controversial. Some winemakers decry any manipulation of the wine-making process. Randall Graham of California’s Bonny Doon takes a more nuanced view5:
Ultimately, however, the appropriate level of alcohol in a wine remains a matter of taste, though we would argue that location and historical considerations of balance regarding a classic style, such as Bordeaux or Barolo, should not be completely laid aside when people decide what appeals to their palate.
2 Winemaker and author Clark Smith, who in California pioneered the use of Reverse Osmosis to dealcoholize wine, provides full technical detail on the process in his recently published book Postmodern Winemaking, UC Press, 2013.
Joel Butler MW and Mike Potashnik PhD