The New York Sugar and Coffee Exchange (NYSCE) established the black bean equivalent system of green grading. It is a measure of comparison for evaluating the relative seriousness of defects. For example, five quakers equal one black bean defect.
Defective coffee beans are very common. Approximately 20% of the coffee beans produced in Brazil each year are defective and need to be removed after harvesting.
Compared with healthy, good-quality coffee beans, immature beans are lighter, less humid, and deficient in key flavour and body precursors, including sucrose, protein, and total oil content.
Colour sorters are not effective at removing quakers from green coffee because their distinctive pale colour becomes exaggerated only after roasting.