In coffee, factors such as geographical location, region, coffee microbiota, microclimate, processing and fermentation parameters, which started in 2014 in general terms, have been widely discussed as factors determining quality and chemicals. It has been observed that microbial growth during fermentation gives additional flavor notes due to metabolites produced in this process. It has been revealed in scientific studies conducted in 2015 that the perception of exotic notes from fermentation processes can be associated with specific compounds detected in this process and that microbiota has an important role in the development of these aromas. As it is known, basic processing methods (natural, washed and semi-washed) have recently been supported by new innovative processing methods. Anaerobic fermentation and carbonic maceration
It has quickly gained popularity in the coffee industry due to the incredible and unique flavors it can produce. Let's examine the terminology here first so we don't get bogged down in the details.
Anaerobic – Oxygen-free environment
Carbonic Maceration – Carbon dioxide rich environment
Maceration - a more inclusive term than fermentation, referring to microbial metabolism, anaerobic and carbonic have a meaning that can be used interchangeably. Both imply limited oxygen. The technique called carbonic maceration was described by Flanzy, Lanzy and Benard (1987) and the first patent was registered by Hickinbotham (1986) for use in the winemaking process to shorten processing time and create a unique body and aroma. Carbonic maceration is defined as a process that investigates the ability of intact fruits to adapt to a closed environment, deprived of oxygen and filled with carbon dioxide (CO2). The addition of CO2 causes a switch from aerobic respiratory metabolism to anaerobic fermentative metabolism in each fruit, affecting the development of the grape microbiota during the fermentation process. Coffee cherries contain many microbial groups, such as lactic acid bacteria, acetic acid bacteria, enterobacteria, and yeasts, which interact during fermentation, and the endogenous metabolism of the beans leads to a specific profile of flavor precursors of green coffee beans. Coffee processing is one of the most important processes for removing damaged beans and improving bean quality, including adjusting its taste and aroma. A 2022 study has shown that the processing conditions and fermentation of coffee berries affect the microbial profile and sensory score of beverages. A 2021 study reported the possibility of a more analytical method to evaluate the quality of coffees by comparing bioactive compounds and minimizing harmful contaminants (i.e. potentially toxic substances such as acrylamide formed during the Maillard reaction during roasting). The general objective of the first study was as follows.
To determine the effect of various processing methods (natural, washed, semi-washed, anaerobic fermentation and carbonic maceration) on antioxidant activity. To determine the content of bioactive and volatile compounds in coffees from different countries (Nicaragua, Ethiopia, Burundi and Peru) and whether different processing methods affect the antioxidant activity and bioactive and volatile compounds in specialty coffees from the same farm. The general objective of the second study was that the change in microbial profile promotes the change in sensory and chemical profile of coffee beans under carbonic maceration and fermentation. Therefore, our aim was to evaluate the sensory, chemical and microbial profile of Arabica coffee after carbonic maceration and fermentation at different times and temperatures. In the first study, 4 different 100% arabica beans were used, namely Nicaragua, Ethiopia, Peru and Burundi. Nicaraguan beans were obtained from the Nueva Segovia coffee region. The coffee was Red Catuai variety harvested in 2020 and was processed in two processes: washed and semi-washed. The Ethiopian beans were obtained from the Sidama coffee region. The coffee was an Heirloom variety harvested in 2020. The cherries in this area are grown at an altitude of 1,200 to 2,000 m. After harvesting, the cherries were placed directly in a closed tank for 7 days of anaerobic fermentation. After fermentation, the beans were processed by farmers using two drying methods called EAO and ACR (ETH-AF-EAO and ETH-AF-ACR). In the EAO method, the beans are dried by carefully placing them under covered African beds for 30 days. In the ACR method, the coffees are dried under sleeping bags in high mountains in African beds to accelerate fermentation. Instead of spreading them, they are put in large piles. The pile grows every day and is thrown into plastic bins at night, aiming to avoid the adverse effects of the weather and to accelerate uniform fermentation for 13-15 days. One person is assigned to each bed and turns the cherries every 15 minutes to ensure even drying. The mixing of coffee cherries prevents mold and ensures that the cherries dry thoroughly, and between 12:00 and 15:00 in the afternoon, the cherries are covered to prevent excessive drying. Burundi beans were sourced from the Kayanza coffee region. The beans were the Red Bourbon variety harvested in 2020. They were processed using two methods: natural and natural anaerobic fermentation. The cherries processed using the natural drying method were harvested by hand and sorted according to their size and quality. During this process, whole coffee cherries are left on the beans to dry in the sun, allowing the fruit to dry around the beans. They are taken to raised African beds where they are dried for 3-6 weeks. The beans processed using anaerobic fermentation were fermented in closed vats containing Cima yeast (Saccharomyces cerevisiae) where they were dried. Peruvian beans were sourced from the Huabal region in the Cajamarca coffee region. The beans were the Catuai variety harvested in 2020 and processed using the carbonic maceration method. In carbonic maceration, the cherries were macerated in a CO2-rich environment after being dried. The ripe cherries were harvested, washed and then spread out on a terrace where they were dried in the sun for 20-25 days. Once this process was complete, the cherries were sealed in water-filled vats with a one-way outlet at the top for 24-48 hours. When the naturally occurring yeast interacts with the sugars of the coffee fruit, carbon dioxide is released. The freshly fermented beans were gently roasted. The time after the first crack for each sample was kept to a minimum and the development time was 90 seconds. The coffees were roasted in 250 g batches.
Experimental measurements;
Total polyphenol content was measured using a modified method for the analysis of phenols and total flavonoid content was measured using a modified method. Bioactive compounds, Chlorogenic acid (5-O-Caffeoylquinic acid, 5-O-CQA), caffeine (CAF), gallic acid (GLA) and cinnamic acid (CNA), were analyzed by high-performance liquid chromatography (HPLC). Volatile components of coffee samples were extracted by SPME and analyzed by gas chromatography-mass spectrometry (GC-MS).
And all these independent analyses were done with 3 different trials for each sample.
The test results are shown in the table below;
To summarize the table;
The washed and unroasted Nicaraguan beans yielded the highest polyphenol content, which was approximately 7 μg GAE/mg higher than the honey-processed version. The total flavonoid content was highest in Peruvian coffees. It was concluded that Ethiopian coffees processed with anaerobic fermentation had higher antioxidant capacity than Peruvian coffees processed with the natural method. The highest gallic acid content among all green beans subjected to different processes was found in Nicaraguan beans. Here, to briefly define gallic acid; Gallic acid, a non-flavanoid benzoic acid subacid, is a phenolic compound. Current studies on gallic acid have shown that it may provide antimicrobial, anti-obesity and antioxidant properties that may improve cancer and brain health.
The measurement results of these coffees in their roasted form;
The total flavonoid content in Peruvian coffee was recorded as the highest in its green form. In addition, the antioxidant capacity was highest in Peruvian coffee processed by carbonic maceration. In Burundi coffee, the total flavonoid was found to be the highest in the roasted form of the green bean processed by the natural method. According to the studies, it was expected that different processing methods would provide additional value to the coffee. The processing method affected the total polyphenol content in some coffees used. Higher polyphenol content was found in fermented coffees than in unfermented coffees. The total polyphenol content was generally higher in green bean compared to roasted coffee. The total flavonoid content in this experiment was strongly discovered in roasted Peruvian. The polyphenol content in roasted coffees ranged from 2.22 to 4.79 μg. In the experimental study titled "Microbial fermentation affects sensory, chemical, and microbial profile of coffee under carbonic maceration", it was proven that anaerobic fermentation of coffee beans and subjecting these beans to different temperatures caused better volatiles to form in coffee and increased sensory profile. In addition, it was recorded that the increase in this sensory profile started at 96th hour in different temperature conditions, in oxygen-free and carbon dioxide environment. While the optimum temperature parameters were 38 degrees Celsius in carbonic maceration of wine, a very wide temperature parameter was obtained in coffee, provided that it was 28 degrees and below 20 degrees, and the day condition was determined as minimum 5. As a summary of the findings of the 2 studies; fermentation strategies promote different biochemical interactions in sensory, chemical and microbiological terms. These strategies also provide control of microbial growth in bean development. In the 2nd study, it was observed that bean cupping score increased up to 85 thanks to the carbonic maceration method performed at 38 degrees for 120 hours and 5 days. One of the most important findings of the two studies was that anaerobically processed coffees contributed significantly to antioxidant activity. At the same time, when compared, relative volatility differences were observed in natural and fermented coffees. In summary, processing of coffee with different fermentation methods greatly affected antioxidant levels, bioactivity and volatility.
DUYGU KURTULUŞ
Co-Founder / Chemist / Nanotechnology Engineer / Hazardous Chemical Consultant / Chemical Evaluation Specialist