[Anaerobic Fermentation Processing Method] Anaerobic (Anaerobic) fermentation has been a very popular post-harvest processing method in recent years. It typically involves placing coffee cherries in a sealed container or fermenting them in water in a washing tank. During this process, different microorganisms are used to ferment and create unique flavors.
The first time I heard about anaerobic fermentation was during the 2015 WBC competition, where an anaerobically fermented coffee from Australian competitor Sasa Sestic stood out. Sasa’s competition beans were fermented in a sealed tank injected with carbon dioxide to expel oxygen. In this oxygen-free environment, the breakdown of sugars in the coffee mucilage was slowed down, as was the drop in pH, resulting in a longer fermentation time. The coffee had a rounder mouthfeel, was less clean compared to aerobic fermentation methods, had higher body, and exhibited more malic/tartaric acid notes.
The characteristics of this anaerobic processing method are: 1. A fully enclosed, opaque container that can be monitored is required; 2. The container is then sealed. Fermentation is essentially the process of converting sugar into various compounds that produce alcohol and carbon dioxide, which generates high pressure inside the sealed container. This high pressure helps the seeds absorb flavor compounds from the mucilage; 3. The container is placed indoors, and the indoor temperature is strictly controlled. Controlling temperature and time allows control over the degree of fermentation in the container; 4. Finally, carbon dioxide is continuously injected into the container to expel oxygen. During fermentation, pH is an important reference indicator. Temperature and pH changes must be strictly controlled. When the sugars in the mucilage and pulp are just completely consumed, the fermentation is immediately stopped by opening the container, and the beans are dried immediately in sunlight to avoid over-fermentation. The wine processing method, also known as carbonic maceration, is inspired by wine-making techniques. Unlike traditional methods where grapes are pressed before fermentation, this method involves placing whole clusters of red grapes directly into a sealed container filled with CO2. After slow anaerobic fermentation, the result is wine with a lighter color, intense fruity aroma, and excellent taste.
Applying this concept to coffee processing, the coffee beans are depulped and then placed in a stainless steel fermentation tank where carbon dioxide is introduced and oxygen is expelled, creating a sealed, oxygen-free environment. This allows the coffee cherries to undergo strictly controlled anaerobic fermentation in the tank, developing more aromatic compounds and high-quality acidity. [Premium Washed Whisky Sherry Cask Fermentation Processing Method] “Sherry casks” are barrels used by the sherry wine industry for aging. Sherry is a famous fortified wine produced in the sunny Jerez region of southern Spain. The sherry production process must include aging through the Solera System.
The Solera System essentially refers to the blending and aging of sherries of different vintages after fortification; In the Solera System, all barrels are stacked by vintage, with the oldest sherry at the bottom and the youngest at the top. Each year, a portion of the sherry is drawn from the bottom barrels for bottling and sale, and an equivalent proportion is replenished from the barrels above.
The premium washed sherry cask fermentation method involves first subjecting harvested coffee cherries to a premium washed process. After washing, these processed cherries are placed in sherry barrels that have previously aged whisky, and fermented at a low temperature of around 15-20°C for 30-40 days, followed by sun drying. The sherry cask fermentation method gives the coffee astonishing aroma and thick mouthfeel. [Raisin Honey Processing Method] The raisin honey processing method from Costa Rica’s Musician Series retains 100% mucilage and uses a zero-water method. Typically, freshly picked coffee cherries are not depulped but are instead placed directly on drying beds to sun-dry until they reach a raisin-like state. Then the skins are removed, the mucilage is retained, and the beans are further dried. During this stage, climatic factors are key to the success of the honey process.
During the drying process, the coffee cherries must be constantly turned to ensure even drying, but the frequency of turning must be carefully managed. The drying should be slow to ensure fermentation, but not so slow as to cause over-fermentation. ；This sweet, raisin-like honey process gives the coffee flavors reminiscent of white wine, balanced acidity, and strong fermentation aromas.
[Lactic Acid Fermentation Processing Method] Lactic acid fermentation achieves a higher concentration of lactic acid bacteria during coffee fermentation through anaerobic methods. Because the most ideal coffee flavors—“body,” “high sweetness,” “caramel,” “wine-like acidity,” and “silky mouthfeel”—all depend on the lactic acid concentration during fermentation.
Before removing the skins, the cherries are placed in a sealed tank. The sugar content, temperature, and pH are recorded; ripe cherries have a high sugar content, providing ample food for naturally occurring yeast and bacteria in the air and on the coffee cherries, leading to fermentation.
One of the byproducts of this fermentation is carbon dioxide. When the tank is sealed, it gradually fills with carbon dioxide, expelling air. Under these anaerobic conditions (i.e., no oxygen), surviving bacteria produce lactic acid, hence the name. After lactic acid fermentation, LPET ferments the coffee cherries in a container for about 70 hours before removing the skins. If you want to know whether coffee cherries have undergone lactic acid fermentation, the simplest way is to observe the beans after removing the skins and pulp. If everything goes smoothly, due to the small amount of alcohol also produced during fermentation, some of the color from the pulp is transferred to the beans.
The dried green coffee beans still need to go through manual sorting before export. In the final sorting process, the ratio of green coffee beans to coffee cherries is about 1:85, meaning LPET on average needs 85 kilograms of coffee cherries to produce 10 kilograms of green beans.
[Animal-Ingested Fermentation Method] The animal-ingested fermentation method is a rather cruel coffee processing method. The most typical example is civet coffee (kopi luwak). Civets are often active at night, using their eyesight and sense of smell to selectively eat the ripest, reddest coffee cherries. The indigestible coffee beans are excreted in their feces, and people then clean and process these fecal beans to obtain these precious, internally fermented beans.
This processing method uses the lactic acid bacteria and digestive fluids in the animal’s digestive tract to replace machines or washing, removing the pulp and mucilage adhering to the surface of the beans. It also enhances the coffee’s flavor and mouthfeel, giving it a unique fermented taste.
