Anaerobic Fermentation has been very popular in the coffee world in recent years, mainly because Sasa Sestic, the Australian competitor who won the 2015 WBC, sparked this trend. Even among the top six competitors in the 2018 WBC, five of them used coffee beans processed with the "anaerobic fermentation method," which shows just how special it is!
In the processing of green coffee beans, "fermentation" is encountered to a greater or lesser extent, and it deeply influences the flavor direction of the coffee beans. Fermentation is generally divided into two types: "aerobic" and "anaerobic." The biggest difference between the two is that the anaerobic process is more uniform and can be controlled, while under aerobic conditions there are too many environmental variables and it is not easy to monitor. Generally speaking, most traditional processing methods are "aerobic" fermentation, and only in recent years has anaerobic fermentation processing gradually developed.
The anaerobic fermentation method, also called carbonic maceration, has processing steps inspired by red wine production, so it is also called the red wine processing method. "Grapes are placed into carbon dioxide gas, causing the grapes to enter an oxygen-free state. In this way, even without yeast, the grapes can convert their own fructose into alcohol, thus producing a special aroma, and the resulting wine has a soft aroma and rich mouthfeel." Returning to green coffee processing, freshly picked coffee cherries are placed whole into sealed metal tanks, and carbon dioxide is injected to drive out oxygen, creating an oxygen-free fermentation environment, reducing the rate of sugar decomposition in the coffee bean mucilage and the rate at which the pH value drops, thereby giving the beans higher sweetness and more distinctive flavors.
The coffee beans Sasa Sestic himself used in the 2015 WBC came from Las Nubes in Colombia and were of the Rume Sudan variety. According to his own account, the anaerobic fermentation method used for this coffee mainly involved placing ripe coffee cherries into a sealed metal container (stainless steel barrel), injecting carbon dioxide, and expelling oxygen, so that fermentation and decomposition could proceed in an oxygen-free environment. Moreover, factors such as the pH value, gas composition, humidity, temperature, and even the types and quantities of bacteria involved in fermentation could all be effectively controlled, developing better sweetness and a more balanced flavor.
However, the green bean processing currently claimed by various processing plants and under the name of anaerobic fermentation is actually not all the same. After all, this type of processing method is still in the development stage, so there is no standard or absolute version. Most of what we hear about now is based mainly on the processing method Sasa used for his coffee beans at the time, or modified from that version. For example, experimental processing methods such as recent anaerobic natural, anaerobic washed, and double anaerobic have appeared one after another, and they are very much anticipated. Adding anaerobic steps to natural or washed processing methods gives us the commonly seen anaerobic natural and anaerobic washed processing methods.
Usinganaerobic naturalfreshly pickedcoffee cherries are placed into sealed barrels for low-temperature fermentation. In an anaerobic environment, the decomposition rate of the mucilage decreases, and at the same time the pH value decreases more slowly, extending the coffee's fermentation time and thus developing more sweetness. The temperature in the entire anaerobic environment must be strictly controlled, averaging 10 to 15 degrees Celsius. After more than three days of anaerobic fermentation, the coffee cherries in the barrel are sun-dried. Finally, after drying is completed, the excess parts of the coffee cherries are removed and the coffee beans are taken out.
For example, the Front Street Colombia Flower Moon Night coffee beans on the Front Street bean list are processed using the anaerobic natural method. This Front Street Colombia Flower Moon Night coffee bean has gained richer ripe fruit sweetness and fermented aroma because of the anaerobic natural process. After roasting, it presents aromas of cranberry, strawberry jam, liqueur chocolate, and cream, as well as a rich fermented scent.
The anaerobic washed processing method, on the other hand, involves subjecting freshly picked coffee cherries to 12 hours of dry fermentation, after which the skin and pulp are removed by machine, and then the coffee beans are placed into sealed fermentation barrels for anaerobic fermentation for 24 to 48 hours. After fermentation is completed, the coffee beans in the barrel are dried. Coffee beans processed in this way present a very rich, fresh, sweet fruit mouthfeel. Front Street Colombia Rose Valley coffee beans are processed using the anaerobic washed method, and when hand-brewed one can sense the aroma of peach and rose.
So-called double anaerobic washed means it is divided into two anaerobic steps. Coffee cherries are processed immediately after picking, and the coffee cherries are placed into a sealed anaerobic environment for the first anaerobic fermentation; after fermentation, the coffee cherries are removed and the skin and pulp are removed in the same way as in the washed processing method, and the coffee beans with mucilage are again placed into a sealed anaerobic environment for a second anaerobic fermentation. Finally, the fermented coffee beans are air-dried and dried, and processing is complete once the moisture content is reduced to 11%.
The feature of undergoing two anaerobic fermentations gives it the name double anaerobic washed. The Front Street Colombia Paradise Estate Sakura coffee beans use double anaerobic washed processing, and because of this processing method they present flavors such as spiced tea, citrus, dark cocoa, and mint.
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The above content is compiled by CoffeeHunters, a coffee news website.
