SUMMARY
Water is the second important ingredient in coffee preparation after coffee type and affects the coffee quality. In this study, it was aimed to investigate the effects of four different water hardness (bottled, purified, medium hard and hard water) used in filter coffee preparation on volatile compounds and flavour of filter coffee. The highest number of volatile compounds were determined in filter coffee prepared using medium hard water (12 furan, 7 pyrazine, 3 pyrrole, 2 aldehyde, 1 furanone, 1 ketone, 1 pyridine and 1 thiophene group, totally 28 volatile compounds). It was determined that the hardness of the water used in the preparation of filter coffee affected the area percentages of 2-methylfuran, 2-methylbutanal, 5-methyl-3-hexanone, 1-methyl-1H-pyrrole, 2-vinyl-5-methylfuran, 2- (methoxymethyl) furan, dihydro-2-methyl- 3 (2H)-furanone, 2-ethyl-3-methyl-pyrazine, 3-ethyl-2.5-dimethyl-pyrazine, 2-furancarboxaldehyde, benzaldehyde, 2.2'-bifuran and 2.2'-methylenebisfuran volatile compounds. Aroma characters (roasted coffee (2.77), roasted hazelnuts (2.35), almonds (0.96), raw vegetables (2.69), soil (0.96)) were perceived in low intensity in filter coffee prepared with hard water. Bitter taste (3.63) was the most perceived taste character in the filter coffee prepared with hard water, while hazelnut (0.40), spice (0.63), lemon peel (0.58), sweet (1.04) and sour (1.52) taste characters were perceived at the lowest level. In filter coffee prepared with medium hard water, the characters of hazelnut (1.63), spice (1.96), lemon peel (3.21) and sweet taste (2.23) were intensely perceived. While sourness was perceived most intensely in samples prepared with soft water (3.55), the intensity of sourness decreased in coffees prepared with medium hard water (2.55), and the lowest sourness was detected in samples prepared with hard water (1.52). According to the results of this study, it was determined that the water hardness affects the flavor of filter coffee, and it is advised to use medium hard water in the preparation of filter coffee to obtain filter coffee containing more volatile compounds.