coffee bacteriome

First-ever characterization study of waste coffee in the drip tray of Nespresso coffee machines indicate the presence of a wide variety of bacteria

Single-serve coffee systems like Keurig and Nespresso are growing increasingly popular for their convenience and variety of coffee ‘pod’ options over traditional drip-coffee machines. A group of scientists from Spain have conducted a first-ever characterization study of bacteria found in used capsule coffee lixiviate, or the leftover coffee waste produced after water has been percolated through the coffee grinds, collected in the drip trays of multiple Nespresso machines.

They aseptically sampled the drip trays of 9 different Nespresso machines located in domestic and communal environments, all of which had been operated for over a year and used 3 to 20 times a day. The drip trays and removable parts of the machines were typically only rinsed with water to clean. DNA was isolated from the collected samples of coffee lixiviate and analyzed for matches to known bacteria.

There were 35 to 67 classes of bacteria identified in each machine sampled. The most abundant variety of bacteria were Enterococcus and Pseudomonas, while Stenotrophomas, Sphingobacterium, and Acinetobacter bacteria were also common. It is surprising to find such as diverse number of bacteria as caffeine is a naturally alkaloid substance which has anti-bacterial properties. Pseudomonas is a reported caffeine-degrading bacterium, but the discovery of Entercoccus may suggest a previously unknown caffeine-degrading ability that could be highly useful for industrial decaffeination processes.

In a separate 2-month experiment, the coffee lixiviate in a brand new machine that was used 5 times daily was also sampled to examine the bacteria colonization process and the variation of bacteria over time. General bacteria that initially grew in the machine were succeeded by a variety of ‘coffee-adapted’ bacteria similar to those from machines operated for over a year. This experiment shows the rapid speed at which a diverse bacteriome can colonize a new coffee machine.

The results from this study not only report that these common single-serve coffee machines are environments where many different types of ‘coffee-adapted’ bacteria can grow, but emphasize between the lines that your coffee machine should be frequently cleaned.



Vilanova, C., Iglesias, A. and Porcar, M. The coffee-machine bacteriome: biodiversity and colonisation of the wasted coffee tray leach. Scientific Reports, 5:17163, 2015.




Written by Fiona Wong, PhD

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