Winespeak: Carbonic Maceration
It’s a trendy winemaking technique, albeit one that is subject to broad interpretation. What is it, and how do you recognize it in the wild?
Rarely does a relatively obscure and technical fermentation method rise in the world of wine to become more famous than many actual wine regions, but such is the case with carbonic maceration—a technique once vilified, now celebrated, and yet still not widely understood. Not only is it a complex process that often occurs beyond observation in closed tanks, its influence on wine style can vary drastically—from subtle hints to an unmistakable stamp.
A process used almost exclusively on red grapes, carbonic maceration is one method for producing fruity, soft, light-bodied, low-alcohol, perfumed, easy-drinking wines without a heavy extraction of tannin or color. It’s a technique vintners might adopt if they wanted to make very approachable wines, increase fruity aromatics in less expressive grapes, reduce acidity, lower alcohol, or establish some “natural wine” street cred.
The spiritual home of carbonic maceration is Beaujolais, in Burgundy, France. It was here where the chemist and winemaker Jules Chauvet experimented with and refined the technique. In the 1960s, Chauvet suggested producers try carbonic maceration to reduce the use of the antibacterial/antioxidant sulfur dioxide, the excessive application of which he saw as a threat to the expression and sanctity of Beaujolais wines. Along the way, he saw that carbonic maceration also reduced acetic and malic acids (also problems in fermentations at the time) as well as offering pleasant aromas and a lighter body. Influential producers began adopting versions of carbonic maceration, and modern Beaujolais was born.
In the 1990s and early 2000s, as American wine culture evolved, a backlash at the lame Beaujolais Nouveau foisted on wine lovers every November often targeted carbonic maceration as a culprit, souring the technique’s reputation. Shortly thereafter, as a new generation adopted better Beaujolais wines, carbonic maceration was looked at more appreciatively. Today, thanks in large part to the natural wine movement, a new generation of winemakers has turned to carbonic maceration because, as Chauvet showed, the process can be an effective alternative to the addition of sulfur. So today you can find light, easy-drinking carbonic wines everywhere—not just in the Gamays of Beaujolais, but in Syrah, Cab Franc, Sangiovese and just about every red grape.
Carbonic maceration occurs when whole, uncrushed bunches of grapes are placed in a closed fermentation vessel that is filled with CO2. In this “reductive” (oxygen-free) environment, the grapes begin fermenting from within (“intracellular fermentation”), but eventually rupture and release their juice as fermentation proceeds. This creates a softer, juicier, more fruit-forward wine, as less tannin is extracted from the skins. There is usually also some “stemminess,” along with scents of bubblegum and/or banana, derived from esters unique to this fermentation method. Also, the wine’s acidity falls a little bit, making softer wines. Very little tannin or color is extracted.
Full, true carbonic maceration is somewhat rare, as it requires specific equipment. First, you need hermetically sealable, usually stainless steel fermentation tanks. After being loaded with whole grapes, these are flooded with carbon dioxide to banish all the oxygen. Second, the grapes must be handled exceedingly carefully, as all the berries must be kept whole and intact. Leaving grapes as whole bunches, helps with this effort, as the stems can serve to protect the grapes, but grapes can also be destemmed, so long as they are not crushed.
Much more common is what’s known as semi-carbonic maceration. The actual recipe for semi-carbonic maceration varies from producer to producer, but, as the name implies, it involves blending carbonic maceration with a more traditional alcoholic fermentation. Like carbonic maceration, semi-carbonic is a whole berry fermentation, but is generally practiced without adding carbon dioxide. As the weight of the grape clusters on top crushes the grapes at the bottom, the alcoholic fermentation begins, producing the CO2 that then fills the tank and creates the anaerobic environment necessary for carbonic maceration.
Wines made through full carbonic maceration will tend to be very light and fruity, as you find with the more commercialized bottlings of Beaujolais nouveau. In these wines, carbonic maceration is employed until the skins break and then the juice is pumped off the skins to finish fermentation without extracting much color or tannin. In semi-carbonic maceration, after the grapes burst the juice is left in contact with the skins to finish the alcoholic fermentation. In this method, some of the characteristics of carbonic maceration are preserved in the final wine, which is darker and more extracted thanks to fermentation on the skins.
If you’ve ever thought you’ve detected Beaujolais-like aromas in a Pinot Noir, Cab Franc, or Syrah, you almost surely have. Carbonic maceration often occurs naturally to some degree in wines fermented whole-cluster, as not all the berries get crushed in the tank, even as the yeast fermentation gets going. So, even in world-class wines like DRC and Allemand, you might often smell carbonic high tones.
There are only a couple downsides to carbonic maceration, as I see it. One is that lower acidity and lack of sulfur make the wines vulnerable to bacterial spoilage, which is a big reason why volatile acidity, brettanomyces, and acetic acid are hallmarks of many natural wines. The other is that the aromatic byproducts of carbonic maceration tend to be the same, no matter the grape or the region. While these aromas are often charming and delicious, to my mind they can be detrimental to unique expression. But, hey, most of the wines I want to drink should be charming and delicious, so bring on the CO2!
Jordan Mackay is a James-Beard-award winning writer on wine, spirits and food. His work appears widely in such publications as Food & Wine, The New York Times, Decanter, and many others. He has written several wine books, including Secrets of the Sommeliers and The Sommelier’s Atlas of Taste (with Rajat Parr) and books on live-fire and meat cookery, including Franklin BBQ and Franklin Steak (with Aaron Franklin). He lives in New York’s Hudson Valley.