During the coffee processing procedure, a remarkable biological operation occurs– microorganisms work to break down coffee cherries, revealing the raw coffee beans inside. After this process, those coffee beans are ready to be dried, roasted, ground, and brewed.

What are Microorganisms?

Microorganisms, also known as microbes, are tiny living organisms too small to be seen with the naked eye. That means you can only see them using a microscope! Life forms like algae, fungi, viruses, and bacteria are all microorganisms.

Microorganisms and Coffee Fermentation

Microorganisms—primarily yeast, bacteria, and fungi—break down sugars in the coffee cherry's mucilage (the substance between the skin and the parchment) in a process called fermentation. The mucilage is a sticky layer surrounding the coffee beans and is removed before drying and roasting. There are two primary methods of coffee fermentation: dry (or natural) and wet fermentation. In the dry process, coffee cherries are left to dry out with their pulp intact, allowing the microorganisms to ferment the fruit naturally over time. The dry method can take several weeks, depending on how dry the environment is. In the wet process, the cherries are de-pulped, and the beans are soaked in water, where the microorganisms break down the remaining mucilage. This process can take 2-3 days.

In both methods, certain microorganisms can alter the coffee's flavor profile. Yeasts like Saccharomyces cerevisiae, or Brewer's yeast, can introduce "unique aroma compounds" to the coffee. Bacteria like Lactobacillus or LAB (lactic acid bacteria) can cause the coffee to have "distinct floral, fruity, or buttery" aromas. Wild strains of fungi and bacteria can result in coffees having unique and regionally distinct flavors.

The Science Behind the Flavor

The role of microorganisms play in the fermentation process goes beyond simply breaking down sugars. They are also responsible for the formation of various organic acids, esters, and alcohols, which directly influence the taste and aroma of the coffee. For instance, the production of lactic acid by lactic acid bacteria can generate a smooth, creamy texture, while the presence of acetic acid bacteria can give coffee a vinegary taste. The diversity of microorganisms is influenced by factors such as altitude, climate, and the surrounding environment, though some can be introduced to the fermentation process manually.

The complex interplay between yeast, bacteria, and fungi in traditional and modern coffee fermentation methodologies results in dozens of different aroma and flavor profiles of coffees worldwide.