Mechanical Damage Causes Potato Taste Defect in Coffee Without Antestia Bug Infestations: Evidence from Experimental Data

Potato Taste Defect (PTD) is a potato-like smell and taste found in green and roasted coffee beans and in brewed cups of coffee. This defect makes coffee unpalatable, hence reducing its value or causing it to be rejected by consumers. Occurrence of PTD in coffee has been associated with Antestia bug damage, Antestiospsi thunbergii (Hemiptera: Pentatomidae), but the processes that lead to the disorder are not well understood. The objectives of this study were: (1) to evaluate whether there is a direct relationship between cherry feeding by antestia bug and occurrence of PTD or if the same defect can manifest mechanically without antestia bug infestations and (2) to assess the relationship between cupping method and Gas Chromatography – Mass Spectrometry (GC-MS) for PTD detection. Treatments consisted of (i) insect damaged beans by caging Antestia bug on coffee branches; (ii) mechanically damaged beans without Antestia bug infestation, and (iii) control beans without any manipulation in the field. At harvest, coffee cherries were wet processed and medium roasted. Detection of PTD was done (i) using organoleptic test following the Specialty Coffee Association of America cupping protocol and (ii) using GC – MS analysis to detect the major compound responsible for the off taste, 3 - isopropyl − 2 – methoxypyrazine (IPMP). High incidence of PTD was found in beans damaged by Antestia bug or mechanically damaged; low PTD incidence was found in control beans. This is the first demonstration that mechanical damage alone in coffee berries can cause PTD in coffee. The lowest amount of IPMP was found in the control beans while the highest was detected in berries with simulated damage. There was a positive relationship between cupping methods to detect PTD and IPMP detection by GC-MS in coffee samples. These results suggest that Antestia bug is not absolutely required to cause PTD but wounds to the berries including feeding damage by this bug would allow entry of Pantoea coffeiphilia, a bacterium responsible for occurrence of PTD in coffee and the subsequent production of IPMP. Elimination of PTD in coffee requires avoiding means of entry for P. coffeiphilia in coffee beans along with proper control of Antestia bug.