16 Methods and Materials Holding samples for two days prior to drying (Treatment 3) produced an ethanol/methanol ratio > 1, whereas all other treatments presented ethanol/methanol ratio < 1. Ethanol/methanol ratio > 1 suggests ethanol fermentation dominates [3]. Ethanol fermentation had a positive correlation with the amount of most volatile mass ions measured by PTR-MS from green beans (Fig. 1). Ethanol content in the beans after roasting was proportional to what was obtained after fermentation (R = 0.937). Ethanol fermentation was also correlated to the contents of the ester family in roasted beans, specifically, to ethyl acetate, for instance (Fig. 2). MFA on DC and analytical results show the presence of these VOCs is correlated with the fermented flavour category in the brew (Figs. 3 and 4). This category includes winey, cognac/whiskey, coffee-pulp and other fermented notes. Introduction Conclusion References Results and Discussion Coffee fermentation volatiles: carry-over through roasting and their effect on brew flavour MARIO R. FERNANDEZ-ALDUENDA, Patrick Silcock*, John Birch and Karen Lusk (*) Corresponding author: pat.silcock@otago.ac.nz Aim 1. Vincent, J.-C., (1987) In: Coffee - volume 2: Technology, (Clarke, R.J., Macrae, R., Eds.); Elsevier Applied Science: London: p. 321. 2. Evangelista, S.R., Silva, C.F., da Cruz Miguel, M.G.P., de Souza Cordeiro, C., Pinheiro, A.C.M., Duarte, W.F., Schwan, R.F., (2014) Food Research International, 61: 183-195. 3. Gibson, A., (1974),East African mild arabica coffee quality characteristics associated with green bean coffee volatiles. Part II: Solai flavour, in 6th International Scientific Colloquium on Green and Roasted Coffee Chemistry. ASIC: Bogota. Treatments Freshly harvested coffee cherries were processed to achieve seven different fermentation treatments (Table 1). Washed coffee (wet method) produced from the same coffee cherries was prepared as a control. After drying, coffee cherries were hulled to produce natural, green beans. A portion of green beans from each treatment was roasted to a standard degree. Analysis Volatile organic compounds (VOC) in green beans were measured using Proton-Transfer-Reaction Mass Spectrometry (PTR-MS). VOCs from the roasted ground coffee were analysed by Static Headspace-Gas Chromatography-Mass Spectroscopy (SH-GC-MS). Roasted samples were analysed by Descriptive Cupping (DC) where certified coffee tasters, described and scored the coffees using the Specialty Coffee Association of America (SCAA) cupping protocol. Green coffee is commonly produced using the wet or dry (natural) process. The wet method has been favoured due to production efficiencies [1]. However, growth in the specialty coffee market has renewed interest in flavours that can be obtained with naturals due to longer fermentation times. Until recently, fermentation as source of desirable flavours had not been assessed [2] and specific contributions of fermentation compounds to natural coffee flavour have not been studied. Drying rate of natural coffee influences the type and degree of fermentation. Fermentation imparts specific flavour characters on natural coffee. Fermentation during post- harvest processing can modify flavour-precursor contents, but also creates some VOCs that can be partially carried over through roasting and impact the cup directly. To investigate the effect of drying rate on the development of flavour during natural coffee fermentation. Figures 1 and 2. – Effect of drying rate of natural coffee during post-harvest processing on (1) Methanol / Ethanol ratio in green coffee beans (PTR-MS) and (2) Ethyl acetate / Methyl acetate ratio in roasted beans (SH-GC-MS). Treatm ent a W > 0.91 a W 0.85- 0.91 a W < 0.85 1 - - - 2 0 0 0 3 ++ - - 4 - + - 5 - - + 6 + + - 7 + - - Legend: (-) – fast drying; (0) – normal drying; (+) – drying delay; (++) – drying suspension. Table 1. – Relative time required to pass through each of three water activity regions for each treatment. 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 1 2 3 4 5 6 7 W Ratio Treatment Fig. 1. Green beans: EtOH/MetOH (PTR-MS) 1A 1B 2A 2B 3A 3B 4A 4B 5A 5B 6A 6B 7A 7B W W -0.1 -0.05 0 0.05 0.1 -0.1 -0.05 0 0.05 0.1 0.15 0.2 F2 (16.11 %) F1 (31.51 %) Fig. 3. Descriptive cupping CA Samples (axes F1 and F2: 47.62 %) Fr_FRUITY Fr_CARAMEL Fr_CHOCOLATY Fr_FERMENTED Ar_FRUITY Ar_CARAMEL Ar_PYROLYTIC Ar_FERMENTED Fl_FRUITY Fl_VEGETABLE Fl_CARAMEL Fl_PYROLYTIC Fl_FERMENTED Af_FRUITY Af_CARAMEL Af_CHOCOLATY Af_PYROLYTIC Af_FERMENTED -0.03 -0.02 -0.01 0 0.01 0.02 0.03 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 0.05 F2 (16.11 %) F1 (31.51 %) Fig. 4. Descriptive cupping CA Descriptors (axes F1 and F2: 47.62 %) Figures 3 and 4. – Correspondence analysis (CA) map representing the projection on F1 and F2 of samples (Fig. 3) and descriptor categories (Fig. 4), for the washed control (W) and the seven treatments, evaluated using the descriptive cupping method. Samples assessed in duplicate (A and B). Cupping sections symbolised by “Fr” – Fragrance, “Ar” – Aroma, “Fl” – Flavour, “Af” – Aftertaste. - 2 4 6 8 10 12 14 1 2 3 4 5 6 7 W Peak area Millions Treatment Fig. 2. Roasted beans: Ethyl acetate (SH-GC-MS))