Sorting of Coffee Beans for 'Potato Defect' in East African Countries



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Since ancient times, coffee has been a savory drink for most of the world's population. It is the second most widely distributed commodity after crude oil in the world. Hence, there has always been a pressure on the coffee industry to produce more volume of good quality coffee. The coffee industry has not been able to meet this increasing coffee demand due to various reasons, such as low crop yield, high coffee rejection rate etc. Historically, the coffee production industry has had high rejection rates due to inadequate knowledge about the defects that plague coffee and the lack of research to detect and eliminate the defective coffee beans.

In this thesis, an attempt has been made to minimize the rejection rate of coffee beans due to a specific defect called "Potato Defect". Potato defect is very prominent in East African countries for reasons not yet known. It is caused by an increase in the concentration of 2-isopropyl -3-methoxypyrazine (IPMP), present in parts per billion concentration in coffee beans. In this thesis, various techniques have been evaluated to detect the increased concentration of IPMP, and then eliminate the 'potato defect' infected coffee beans. As these proposed techniques need to be implemented on an industrial scale, special care has been taken to keep the inspection time of coffee beans as low as possible to minimize its negative impact on the overall coffee production rate.

Considering both sensitivity and time, non destructive methods such as ion mobility spectrometry, cavity ring down spectrometry and electronic nose were assessed for their suitability to identify low concentrations of IPMP in the complex matrix of coffee volatiles. Experiments were also conducted by Solid Phase Micro Extraction (SPME), followed by multidimensional gas chromatography with simultaneous olfactory and mass spectrometric detection (GC- MS-O) technology to validate information related to the 'potato defect'. GC-MS-O could detect IPMP present in whole green coffee beans while other researchers only detected IPMP in ground coffee.

The findings of this thesis opens the doors for the coffee industry to establish non destructive, sensitive methodology to analyze further coffee aroma.