The Role of Microbes in Coffee Fermentation and Their Impact on Coffee Quality

Coffee is one of the most important and widely used commercial crops in the world. After ripe coffee cherries are harvested, coffee must pass through several steps to become (green) raw coffee beans. Commonly, there are three different processing methods used to obtain green coffee beans from coffee cherries, namely, the wet, dry, and semidry methods. Microorganisms (yeasts and bacteria) play a major role in coffee fermentation process by degrading mucilage by producing different enzymes (pectinase), acids, and alcohols. Starter culture development is crucial and is done by selecting microorganisms that have certain characteristics, such as mucilage degradation ability, tolerance to stress during fermentation, the ability to suppress the growth of pathogenic fungi, and a positive impact on the sensory quality of the coffee. Currently, green coffee beans obtained from farms that use any of the above processing methods are fermented with selected microorganisms to improve the flavour and aroma of the coffee. This is the result of a new insight into the development of unique flavoured coffee and into engaging with the coffee market to better benefit. This review gives a comprehensive overview of the fermentation process, microorganisms and starter cultures, and fermentation's impact on coffee quality. Future prospects are also discussed through the incorporation of recent research.