2.1. Coffee samples and chemicals

Samples of commercial Arabica and Robusta green coffee were sourced from UK and European importers with the aim to obtain a wide geographical and botanical distribution of batches. A total of 25 coffee batches were used, and from each batch 10 beans were randomly selected. The batches were commercial samples from several growing locations, namely Brazil, Colombia, Costa Rica, Ethiopia, India, Mexico, Honduras, Kenya, Nicaragua, Uganda, Rwanda and Vietnam. The dataset included samples that had been treated using both the wet (∼60%) and dry (∼40% of the total batches) post-processing techniques, in order to include all possible variation expected on new real samples on the market. As soon as the samples were received, they were stored in a storage room at controlled temperature (∼10 °C) and humidity. These coffee beans represented the samples individually analysed in the current experiment. Reference chemical compounds for the volatile compounds analysed by GC–MS were obtained from Sigma-Aldrich (Steinheim, Germany), and Fluka (Buchs, Switzerland). The following compounds were used as standards for the GC–MS analysis: 2,3-pentanedione (97%), hexanal (98%), 1-methyl-1H-pyrrole (98%), 2-methyl-pyrazine (99%), 3-hydroxy-2-butanone, 2,5-dimethylpyrazine (98%), 2,6-dimethylpyrazine (98%), ethylpyrazine (98%), 2,3-dimethylpyrazine (99%), 2-ethyl-6-methylpyrazine (95%), 2-ethyl-5-methylpyrazine (98%), 2-ethyl-3-methylpyrazine (98%), acetic acid (99.5%), acetoxyacetone (98%), 2-ethyl-3,5-dimethylpyrazine (47.5%), 5-methylfurfural (99%), 2-furanmethanol (98%), 3-methyl-butanoic acid (98%), guaiacol (98%), 4-ethylguaiacol (98%) and 4-vinylguaiacol (98%).