Potato Defect is a unique and unusual defect found only in coffees from Burundi and Rwanda. It is caused by unknown bacteria entering the coffee cherries’ pods and producing a toxin that generates an unpleasant taste.
Some studies show that: Potato Defect occurs when airborne bacteria get into a puncture or tear in the outer skin of a coffee berry. Such failures can happen for several reasons. The most common cause is Antestia ( Antestiopsis orbitalis ), a tiny, blood-sucking insect that creates holes outside the coffee fruit that allows bacteria to enter.
Potato defects are not harmful to health, but they give off a characteristic aroma when roasting and grinding coffee, like the smell of a raw potato. Potato Defects can only be detected after the coffee has been prepared, so a coffee roaster cannot detect this form of defect in a batch of coffee until it is made into a drink.
The problem is that the Potato defect does not appear in bulk but only on a few individual beans. Hence, although it affects the flavor of the whole batch of coffee, it is tough to identify and remove the defective beans. Difficult.