Identification of ethyl formate as a quality marker of the fermented off-note in coffee by a nontargeted chemometric approach.

The quality of coffee is influenced by many factors such as coffee variety, agricultural and postharvest conditions, roasting parameters, and brewing. The pleasure of drinking coffee may be affected by off-notes such as burnt, green, earthy, or fermented. Their presence is related to the variety, fermentation during postharvest processing, or over-roasting of the beans. Sensory expert panels trained for the evaluation of coffee are able to detect off-notes and select coffees by well-defined quality criteria. The application of instrumental approaches detecting quality markers related to the perceived off-notes is shown to be useful to assist sensory panels. This paper describes the discovery of a new marker compound related to the fermented off-note occasionally perceived in coffees. The application of untargeted chemometric methods on volatile compounds revealed correlations between individual compounds and the sensory attribute. The new marker compound was identified as ethyl formate, which can be measured in the headspace of roasted and ground coffee by various analytical techniques including online proton transfer reaction mass spectrometry.