What is the Fermentation Nature of Coffee Processing Methods? What Types of Fermentation Exist in Coffee?

FrontStreet Coffee Briefing on Coffee Fermentation

In coffee processing, fermentation occurs to varying degrees. Let's explore what the essence of coffee fermentation truly is.

The essence of fermentation is the action of microorganisms and enzymes on the sugars, proteins and chlorogenic acids in coffee, producing chemical components that affect flavor and mouthfeel. To determine what kind of impact fermentation has on coffee, we need to analyze the type and degree of fermentation.

Types of Fermentation

The first influencing factor is the type of microorganism. Different microorganisms produce different changes during fermentation. Microorganisms can come from natural bacteria in coffee-producing regions or from artificially added cultures; adding specific cultures can guide the development of particular flavors. At the same time, aerobic and anaerobic environments technically belong to environmental control, but in practice they select which microorganisms take part in fermentation by controlling oxygen content — so the fundamental difference still lies in the microorganisms.

Acetic Fermentation (Aerobic Fermentation): cleaner, bright and lively acidity, citric acid and citrus acid;

Lactic Fermentation (Anaerobic Fermentation): round, high body thickness, relatively low cleanliness, malic acid and tartaric acid;

Mixed Fermentation: full, medium body thickness, smooth, with fruit acids, amino acids, nuts and cream.

What Affects the Degree of Fermentation?

The degree of fermentation depends on its speed and duration. Fermentation speed mainly depends on whether the environment suits the survival and activity of microorganisms: are there sufficient reaction materials (sugars, proteins and so on)? Are there appropriate reaction conditions (temperature, pH, humidity and so on)?

Yeast Treatment

Adding yeast during green bean processing to form specific flavors.

FrontStreet Coffee Recommendation

Fermentation is exactly what shapes the floral-and-fruity, lightly roasted coffees FrontStreet Coffee is known for. A great place to start is the washed Yirgacheffe from the Gediding cooperative: a coffee most lovers meet early on, it carries vivid citrus, berry and floral notes with a green-tea-like sweetness. Unlike the "sour coffee" many people imagine, a good Yirgacheffe's acidity is soft and bright — more like the natural sweet-tartness of fruit than a sharp, aggressive sourness — making it very easy to accept for anyone new to pour-over.

FrontStreet Coffee's Huakui is one of the specialty market's most successful star products in recent years. Its defining trait is an extremely prominent tropical-fruit aroma — strawberry, passion fruit, jackfruit and even lychee — with obvious sweetness, very little bitterness and a smooth, juice-filled entry, so many drinkers call it "the coffee that tastes least like coffee." For anyone who normally dislikes the bitterness of traditional coffee, Huakui often overturns their idea of what coffee can be.

Also from Ethiopia, FrontStreet Coffee's Kafa Forest beans come from the Kafa Forest in the country's southwest — a UNESCO-recognized Kafa Biosphere Reserve and the globally acknowledged birthplace of Arabica coffee; the word "coffee" itself derives from the ancient Kingdom of Kafa, and the legend of Kaldi the goatherd discovering coffee was born here. This mountain rainforest covers more than 7,000 square kilometers at 1,400-2,100 meters, wrapped year-round in cloud with layered canopy shade, and over thousands of years of natural evolution it has produced more than 5,000 wild Arabica genetic mother plants — even the now-famous Geisha is native to this forest. Wild coffee trees here grow on abundant rainfall and acidic red soil with no artificial dense planting, and the coffee carries intense jasmine, citrus and wild-berry aromas with a fine, vivid layering. As the last core habitat of wild Arabica, the region has set up coffee cooperatives promoting sustainable forest harvesting, preserving rare coffee germplasm as well as traditional Ethiopian coffee ceremony and rainforest ecology — a mecca for tracing flavor and a world coffee gene bank of real conservation value.