What is a Sour Bean?
In coffee cultivation and processing, "sour beans" refer to coffee beans with a defect caused by excessive fermentation, where bacteria or mould attack the seed. This defect can result from over-fermentation, falling to the ground, or excessive time between harvest and processing. Sour beans can be identified by their yellow to brown colour and the sour, fermented, acetic, fruity, sulfurous, or vinegary taste they impart to the coffee. Sours are considered a major coffee defect and can significantly affect the quality of the coffee.
Coffee beans affected by sours are typically sorted out during processing to ensure that only high-quality beans are exported. Prevention is the best method for avoiding sours; ensuring that coffee is processed promptly after harvesting, with proper fermentation times and drying techniques, can help prevent the occurrence of sours. Additionally, good agricultural practices such as careful harvesting, sorting, and transportation can also help reduce the risk of sour beans. Coffee professionals, such as roasters and importers, should be aware of the potential for sour beans and carefully inspect green coffee samples to avoid purchasing affected coffee.