How Does CM Processing Shape Coffee Flavor?

CM stands for Carbonic Maceration, an anaerobic fermentation style that gives coffee richer aromatic layers while limiting sharp acetic acid flavors. It has evolved since its introduction and helped competitors win the World Coffee Championship in 2015 and 2018. Five of the top six finishers at the 2018 WBC used anaerobically fermented beans, showing how far coffee processing has moved beyond natural, washed, and honey methods.

Variety sets a coffee's flavor potential, but coffee bean processing decides how much of it reaches the cup. The same variety can taste entirely different depending on fermentation method, microbial activity, and drying. CM has become closely tied to competition beans, though fermentation can also lower cupping scores when it goes wrong.

Coffee processing methods have long ceased to be limited to natural, washed, honey, and wet-hulled techniques. In recent years, a method called CM processing has gradually entered the public eye. CM stands for Carbonic Maceration, which belongs to the anaerobic fermentation family. It allows coffee to present richer aromatic layers while suppressing the production of sharp acetic acid flavors. Since its inception, this processing method has continuously evolved and has twice helped competitors win the World Coffee Championship, in 2015 and 2018. This article will systematically sort out the origins and development of CM processing from perspectives including fermentation principles, microbial action, and fermentation differences among various processing methods, and explore its actual impact on coffee quality and flavor expression.

When it comes to coffee bean processing methods, classic approaches such as natural, washed, honey, and wet-hulled are already familiar to everyone. However, in recent years, a craft called CM processing has begun to appear frequently in discussions.

CM processing method

what exactly does it refer to?

There are many types of coffee bean processing methods. Although variety fundamentally determines coffee's flavor genes, using different processing techniques can make coffee beans of the same variety display completely different flavor characteristics. The most prominent processing method today is undoubtedly "anaerobic fermentation."

In recent years, coffee beans processed with "anaerobic fermentation" have repeatedly achieved excellent results on the stage of the World Barista Championship (WBC) finals, and CM has almost become synonymous with "competition beans." Among the top six competitors in the 2018 WBC, five chose "anaerobic fermentation" coffee beans as their weapon for competition.

“Carbonic Maceration”, written in English as Carbonic Maceration, abbreviated as “CM processing.”

The CM processing method can give coffee a more complex aromatic expression while reducing the appearance of sharp acetic acid flavors.

Since its birth, the CM processing method has also continued to iterate and evolve, winning the world championship twice, in 2015 and 2018, which is strong evidence of its successful evolution.

Fermentation can indeed help us improve coffee quality, but in some cases, it may also cause cupping scores to drop by at least 8 points. Especially when we cup specialty coffee scoring between 80 and 92 points, an 8-point gap is by no means a small matter.

From a scientific perspective, fermentation involves metabolic processes and also the process by which organic molecules release energy under anaerobic conditions. In the food and beverage industry, fermentation is usually used to describe the changes that occur in food under the action of microorganisms such as bacteria or yeast. This process produces ethanol (alcohol), carbon dioxide, and lactic acid and acetic acid. In short, fermentation is the process by which sugars and starches are broken down into acids or alcohol.

Yeast and bacteria play key roles in fermentation. Yeast is a microorganism, a natural wild yeast, widely present on the surfaces of grapes, cocoa beans, and other fruits. It appears in winemaking and in the processing stages of cocoa beans and coffee beans. As for bacteria, lactobacillus is representative.

Components of fermentation

Generally speaking, almost all coffee beans undergo some degree of fermentation during processing. Fully washed coffee beans basically all go through a consciously controlled fermentation stage, and after the coffee fruit has its seeds removed, it usually ferments overnight. Sometimes this is done by soaking the coffee beans in water before washing, channel grading, and drying. After fermentation is complete, continuing to soak in water can reduce the number of microorganisms, but fermentation does not completely stop during the soaking stage.

Coffee beans processed by natural drying or pulped honey natural drying also undergo external fermentation. As the moisture in the coffee beans gradually evaporates during drying, microorganisms actively break down the sugars in the fruit or in the pectin mucilage on the coffee bean surface, thereby changing the flavor direction of the coffee beans.

Unlike winemakers, who select specific yeast strains for wine fermentation, coffee growers rely on the microorganisms and yeasts carried by the coffee beans themselves for fermentation. In this respect, coffee bean fermentation is more similar to cocoa. Many coffee beans with unique origin flavors contain inherent microbial communities. After fermentation, these natural components, influenced by terroir conditions and cultivated varieties, play an irreplaceable role in flavor presentation.

There is no perfect coffee variety, nor is there a perfect process. But if we can understand more deeply the complexity of flavors in different coffee varieties and their strengths and weaknesses, and at the same time grasp the possibilities of CM processing or other controllable fermentation methods, it may be possible to maximize strengths and avoid weaknesses, highlighting the advantages of coffee beans and compensating for their shortcomings. Once we find the ideal fermentation formula, we will be able to have the technology and ability to replicate specific flavors.

The above content is compiled by CoffeeHunters, a coffee news website.