From the green bean to the cup of coffee: investigating coffee roasting by on-line monitoring of volatiles

Abstract

Volatile organic compounds (VOCs), emitted from green coffee beans, during coffee roasting and from a cup of coffee, were all analysed by proton-transferreaction mass spectrometry. Firstly, the headspace (HS) of green beans was investigated. Alcohols dominate the HS, but aldehydes, hydrocarbons and organic acids were also abundant. Secondly, we roasted coffee under two different conditions and monitored on-line the VOCs emitted during the process. In a first roasting series, a batch of beans was roasted. After an initial drying phase, dominated by evaporation of water and methanol, the HS concentrations of VOCs such as acetic acid, acetaldehyde, pyridine and methylbutanal rapidly increased and went through a maximum at medium roast level. In a second series, just six beans were roasted. We observed sporadic bursts of some volatiles (furans, butanal, 2,3-pentanedione), coinciding with popping sounds. Other VOCs showed smooth time-intensity profiles (pyridine, pyrazine). These experiments gave a real-time insight into the complex processes taking place during roasting. Finally, the HS of coffee extracts, prepared from beans roasted to different roast levels, were analysed. Most VOCs showed a maximum concentration at medium roast level (e.g. pentanedione, furfural, 5-methyl furfural), while others showed a gradual increase (e.g. pyrrol) or decrease (e.g. methanol).

HS-SPME/GC/MS profiles of convectively and microwave roasted Ivory Coast Robusta coffee brews

“…One of the principal technological processes is roasting that gives rise to the formation of the characteristic flavour and taste of coffee brews ( Yeretzian et al 2002). The aroma of roasted coffee depends on the variety of coffee, agricultural factors, post-harvest treatment, and the conditions of storage and roasting (Hashim & Chaveron 1996;Semmelroch & Grosch 1996;Sanz et al 2002;Mondello et al 2005).…”

Volatile compounds profiles in unroasted Coffea arabica and Coffea canephora beans from different countries

“…Propanal was identified by Yeretzian et al (2002) in green coffee and in green robusta coffee by Nebesny et al (2007). Pentan-2-ol was marked in green Arabica coffee beans in the study by Bertrand et al (2012).…”

“…Beznene acetaldehyde (Phenylacetaldehyde) was also marked in green coffee beans in the study by Cantergiani et al (2001), Yeretzian et al (2002) and in green coffee beans (Coffea arabica) from Hawaii (Lee & Shibamoto, 2002). Also Fisk et al (2012) found these compounds in their study of roasted and ground coffee and Mestdagh et al (2014) in coffee beverage.…”

“…2-methylpropanoic acid (isobutanoic acid) was marked in green coffee beans in the study by Yeretzian et al (2002) and in green Mexican coffee by Cantergiani at al. (2001); methyl hexanoate (Hexanoic acid) (Table 2, 3 and 4) was marked in green coffee by Cantergiani at al.…”

“…(2001); methyl hexanoate (Hexanoic acid) (Table 2, 3 and 4) was marked in green coffee by Cantergiani at al. (2001), Yeretzian et al (2002), by Toci & Farah (2008) in black-immature coffee beans and by Bertrand et al (2012) in green Arabica coffee beans. 2-propionylpyrrole (1H-Pyrrole) was found in roasted coffee (Toci & Farah, 2008), in green Mexican coffee (Cantergiani et al, 2001) and in black coffee beans (Agresti et al, 2008).…”