Wild Harenna coffee: flavor profiling from the cherry to the cup

Coffee is one of the world’s most popular beverages, representing a major source of income for many producing countries. The typical aroma is certainly the reason of its success: it depends on the coffee variety, with its specific set of chemical precursors, as well as on the processing and consumption phases [1]. In the Harenna Forest, in the Bale National Park of Ethiopia, at an altitude of around 1800 meters, an Arabica wild coffee grows spontaneously: the Harenna Forest Wild Coffee Presidium recognizes the value of this unique and high quality product, which has been bestowed the Slow Food Presidium in 2012. It is naturally dried in loco and its exports volumes are limited, as its availability is greatly variable. The aroma of coffee is a complex bouquet of odorants of different origin: the evaluation of its composition could be used as a tool for the coffee industry to control desirable flavor outcomes of coffee through processing or other farm management technique. In this perspective, the Head-Space analysis could represent a simple, fast and accurate technique to evaluate the development of flavor-active compounds in all the phases of the coffee production. In the present study, the volatile aroma profile of Harenna wild coffee has been analysed by means of HS-SPME-GC/MS from the coffee cherry to the coffee cup, all throughout the processing phases which lead to the final product. The dried green cherries, rich in monoterpenes (especially dihydro myrcenol and limonene), esters (mainly cis-2-tertbutyl- cyclohexanol acetate), alkanes, and phenylpropanoids, also contain the precursors for the aroma compounds formation through the Maillard reaction, which takes place during the roasting phase. Pyrazines (mainly 2,6-dimethylpyrazine, 2-ethyl-6-methylpyrazine, and 2,3,5-trimethyl pyrazine) begin to be detected at 100 °C, to become the most abundant chemical class on the later roasting phases, when the temperature reaches 160, 180, and 204 °C, the final roasting temperature. Pyridines (mostly pyridine) are also developed during the roasting phase: they are only detected in the samples roasted over the temperature of 160 °C. Furans (mostly 2-furan methanol, 5-methyl furfural and furfuryl acetate) are also developed through thermal treatment, while monoterpenes decrement as they are volatilized very soon in the roasting process. This is also confirmed by their detection in the coffee silverskins, for which the volatiles emission profile is similar to the green cherries one: they retain the early-released volatiles as they are soon separated from the cherries in the roaster.