Carbonic maceration is a 19th-century technique (which was probably practiced in some amount, or in a hybrid style, much earlier) currently enjoying an en vogue resurgence in some parts of the US wine industry. It is defined by a zero or limited-oxygen fermentation, in the presence of at least a portion of whole grape berries (i.e. not destemmed). Typically associated with Gamay reds from the Beaujolais region of France, carbonic maceration yields very distinctive fragrances and mouthfeel effects. In my experience, the results are low-tannin, lower-color, and highly aromatic wine (veering into the rarefied world for still red wines, at least) with some artificial strawberry, cherry candy, and even notes of fake banana flavor. In fact, amyl acetate, which is often used in commercial food production as an artificial banana flavor, is often naturally produced by yeast under carbonic maceration conditions.
So why would you want to do it if it’s so, well, odd? A lot of the winemakers who use it, myself included, do one or two carbonic lots every year so we end up with some lower-tannin, fruitier blend components to play with. It can be a fun part of your cellar spice box and can lend some je ne sais quois, to blends. A few wineries will go all out and bottle a “100% Carbonic” style red or light red wine without blending, though this is rare as that combination of flavor and aroma characters are less acceptable to the general American marketplace. With a country brought up in the last thirty years to think of Cabernet, Zinfandel, or a big red blend as the only “proper” red wine, it can be a hard sell.
My husband and I toured the Beaujolais and Rhône regions in France last year and with all the tasting we did in the actual cellars in Beaujolais, decided that we didn’t really care much for the carbonic-macerated red wines produced in that region. We can appreciate them for what they are — minimally- handled, low or no-oak, fresh wines with distinct aromas — but we also found them sharp, too acidic, and not very appealing. We vastly preferred the reds of Hermitage and Chateauneuf-du-Pape.
That doesn’t mean that you can’t try a little carbonic maceration in your home cellar, of course. Though definitions vary, a carbonic maceration process would be something like this:
• Pick whole-cluster red grapes, preferably at night/early morning so they stay cool.
• Do not destem.
• Create an oxygen-poor environment by adding carbon dioxide gas or dry ice in the fermenter.
• Put whole clusters into fermentation vessel, keep cold, around 52 °F (11 °C) (optional), adding a lower level of SO2 than you normally might use, as long as fruit is sound. Try about 15-25 ppm total SO2 addition. You want the wild yeast to contribute some of their interesting aromatics before stronger yeast take over.
• Keep a lid on the fermenter.
• Exclude oxygen for as long as possible.
• Let the tank sit for…….how long???
And so begins the tricky part, where a winemaker needs to decide how long they’re going to leave the lid on this pressure cooker before letting the tank warm up and a more traditional fermentation take place to completeness.
You see, if you just have 100% intact berries in an oxygen-deprived environment, the grape berry cells will start a chemical breakdown process whereby they will consume a small amount of carbon dioxide, malic acid, and sugar and will actually produce a small amount of alcohol, about 1-2%. Acidity is naturally reduced in this process and additional aromatic compounds are generated (the aforementioned artificial candy and banana flavors). The cells in the grape eventually die and this unique intracellular process becomes inactive at this point. That’s why you want a wine yeast to take over at some point.
However, no matter what happens, even with 100% whole clusters and cold storage temperatures, you’re going to have berries at the bottom of your tank or fermenter that will be crushed by the weight of the grapes on top of them. The released juice is full of sugar which will begin to be metabolized by the ambient yeast who either came in on the grapes or your winemaking equipment.
The key to harnessing the carbonic maceration technique in a positive way is to allow enough time for the intracellular fermentation to take place but not so much time that bacteria take over and start producing undesired compounds like ethyl acetate and acetic acid (volatile acidity or VA).
In my experience using this carbonic maceration technique, after day 1, I’ll let the tank warm up naturally over a few days then take the top off the fermenter. About day 5 or 6, I’ll introduce a small amount of yeast culture into one side of the fermenter. This ensures that you capture the interesting aromas produced during that first intracellular fermentation but then that you introduce a yeast strong enough to take the fermentation to dryness.
Additional interesting benefits (some might call them “side effects”) of carbonic maceration are related to texture. The intracellular fermentation will naturally degrade some of the malic acid, and if followed by a traditional malolactic fermentation, the malic acid level will degrade even further, resulting in a lower-acid final result. With whole bunch fermentation, sugars are released more slowly into the fermenter, prolonging the number of days of fermentation but also often producing extra glycerol which can be a positive mouthfeel and body contributor.
One can also do a very attenuated carbonic maceration by doing all of the above steps but just leaving the fermenter with the lid on tight for a day or two only and not putting in as much dry ice or carbon dioxide gas to start with. This allows some of the intracellular fermentation as well as some of the indigenous yeast to gain a foothold before inoculating with a yeast that you know can finish the job. This kind of approach is very common in my cellar today, where I let the indigenous mix of yeast and bacteria “get a little naughty” and aromatically funky before I encourage the fermentation to go to completion with a consistent predictable yeast strain.
So is carbonic maceration worth trying? That all depends on your wine style goals. If you’re not sure, try a bottle of Beaujolais Nouveau and see if you like it. You can also try a “Wine Wiz Style” attenuated carbonic maceration start to fermentation, yet finish it in almost a completely traditional way. Whichever you choose, happy macerating.