Understanding the Process: Carbonic Maceration

Continuing our series on coffee processing, we know about carbonic maceration—a unique, newer processing recipe.


Photos courtesy of Cafe Imports

Editor’s note: Check out more entries in our “Understanding the Process“ series here.

The rise of the specialty-coffee scene has helped most people know that talking about coffee as something that always tastes the same—usually dark and bitter, with no distinctive flavor—is reductive. Flavor notes can vary from hints of dark chocolate to candy peach to jasmine. These depend on lots of factors, including coffee varieties, origin, processing, and roasting style. 

Carbonic maceration is one of the lots of interesting coffee processes—and one that was developed more lately. The technique involves the utilize of carbon dioxide to soften the tissue of the coffee fruit. So what exactly is carbonic maceration?

A blue bucket of coffee seeds, already darkened by processing.
Carbonic maceration is an anaerobic recipe that introduces unique aromas to coffee seeds.

Carbonic Maceration Pointed out

Taya Brown, Ph.D., coffee production researcher and educator at Cafe Imports, can help us know more about it. 

Carbonic maceration, Taya explains, is a form of anaerobic processing. The term is borrowed from a winemaking process where bunches of grapes are fermented in tanks with their stems. Carbon dioxide is then pumped directly into the tanks. ”Including skins, seeds, and plant material under these particular environmental circumstances is a way to infuse the wine with tannins and other compounds existing in those tissues, nevertheless without having these impart their sometimes unpleasant aromas,” Taya says. ”Essentially, it’s a way to increase and enhance the flavor of what might otherwise be less flavorful and enjoyable wines.”

Nevertheless how exactly does it work when we talk about coffee? 

A coffee worker points to the nozzle on a blue tank roughly half his height. The room is full of wooden barrels stacked along the wall, and he stands next to a stand of blue barrels. The nozzle has a red cap to keep air out of the tank. Another worker observes.
In carbonic maceration, whole coffee cherries are sealed in airtight tanks, with carbon dioxide pumped in, which forces oxygen out.

How It Works

The technique is really similar for coffee, says Taya. “We ought to remember that comparisons between wine and coffee break down pretty quickly—one of the main differences is that the product we consume in wine’s case is the fruit and juice that undergoes the fermentation. In coffee it’s the seed we’re after, and that seed goes through a lot more than wine does before we consume it. The coffee seeds/beans sit through fermentation of the fruit’s flesh … (then are) cleaned of that fruit, dried, and stored, then roasted and made before we ever taste it. The current definition of carbonic maceration in coffee refers to whole cherries sealed in a container with Carbon Dioxide (CO2) actively pumped into it. CO2 creates pressure and pushes oxygen (O2) out, resulting in an anaerobic environment. CO2 is thought to favor a different metabolic force than open-air fermentation, and likewise may reduce oxidation of fruit and seed tissues.” 

While factors such as time and temperature can help create a range of different tastes, often carbonic maceration coffees have “intense flavor profiles, with boozy and cooked fruit flavors,” Tanya says. Of course, some of them are sweeter, and some more acidic. If things don’t go right, “they also run the risk of astringency, dryness, and bitterness,” she adds. 

Risk and Rewards

Taya shares her point of view on the pros and cons of carbonic maceration. 

“One thing to appreciate about carbonic maceration is the ability to control variables and target specific outcomes for coffees. Anaerobic fermentation offers a way to control the environment the coffee sits in during fermentation and, with the introduction of CO2, carbonic maceration can offer yet another degree of control. Nevertheless, to technique coffees this way needs tanks that can be sealed, one-way valves to let the O2 out and release pressure as CO2 builds up.” These tanks can be a big investment, so they may not be within reach for all producers.

Three workers sift through coffee cherries by hand. The cherries are loaded on a large tarp, and are being checked for cherries that aren't suitable for processing.
Producers sift through coffee cherries to remove defects.

Taya cautions that carbonic maceration callsfor an intimate understanding of the variables involved and a view of the end goals. Among the many important necessities is the ability to cup. ”It’s very difficult for producers to experiment, and to invest in specialized tool if they can’t cup their experiments,” Taya says. ”Many producers do have access to cupping labs, however the majority of in the world do not. Without the ability to know what the outcomes are, adding CO2 simply doesn’t offer the benefit of a controlled variable—you have to have a short feedback loop to discover flavor and quality shifts as investments are brewed and new processing steps are trialed. While it’s exciting to have new terminology, new flavor profiles, and for producers to have new avenues of appreciate addition and differentiation to explore, new processes also require investment and carry a degree of risk.” 

Blue tanks are lined neatly against a brick wall on wooden pallets. They each have a valve on top for pumping in CO2.
The tanks essential for carbonic maceration are an investment. If handled well, they reduce oxidation to coffee seeds and produce smooth tastes.

Taya’s Takeaway

As a final note, Taya adds a clarification on terminology when it comes to the carbonic maceration technique. 

“One thing to note is that, literally like with other types of anaerobic processing, carbonic maceration is truly one step and can be combined with several other steps, along with all major processing types—washed, honey, and natural,” Taya says. “In my opinion, we do a disservice to call a coffee ’an anaerobic’ or ’a carbonic maceration,’ due to the reality that we’re then ignoring any other steps a coffee went through. It would be more accurate to say ’a natural/honey/washed coffee fermented in an anaerobic environment for X number of hours.’” 


Tanya Nanetti (she/her) is a specialty-coffee barista, a traveler, and a dreamer. When she’s not behind the coffee brewing tool (or visiting some hidden corner of the world), she’s busy writing for Coffee Insurrection, a website about specialty coffee that she’s creating along with her boyfriend.

The post Knowledge the Process: Carbonic Maceration appeared first on Barista Magazine Online.

This article was first published at Barista Magazine, an online magazine dedicated to baristas and coffee professionals.