The taste of potatoes in coffee can be attributed to what is referred to as the Potato Taste Defect (PTD). Studies have shown that the phenomenon to be caused by a chemical called 2-Isopropyl 3-methoxy pyrazine (IPMP). The defect is considered a “taste” defect and has not been found to have any health consequences. It’s generally found in coffee from East Africa but its overall prevalence is very low.