Flotation Sorting

Flotation sorting is one of the first critical quality control steps in coffee processing. When coffee cherries are harvested, they are often brought to a washing station or wet mill and dumped into large tanks filled with water. This process relies on the principle of buoyancy to separate the harvest into different quality tiers.

In practice, ripe, healthy coffee cherries are dense and will sink to the bottom of the tank. Conversely, cherries that are under-ripe, over-ripe, or damaged by pests like the coffee berry borer are less dense and will float. By skimming off the floating cherries, producers can effectively remove a significant portion of potential defects before the more intensive processing stages begin.

This method is essential for maintaining the consistency of a lot. If light, defective cherries are allowed to remain with the high-quality fruit, they can introduce off-flavors, such as medicinal or rubbery notes, during fermentation and drying. By removing these early, the producer ensures that only the most uniform, sugar-rich cherries proceed to the depulping or drying stages.

While simple, flotation sorting is a highly effective, low-cost tool for quality management. It is widely used in both washed and natural processing methods. For the consumer, this means a cleaner cup with fewer defects, as the sorting process helps ensure that the final roasted coffee is free from the negative sensory impacts of low-quality or damaged fruit.