Impact of Water Composition on Coffee Sensory Properties: A Comprehensive Analysis

Water quality and the composition of minerals in the water impact coffee extraction and thus influence the sensory experience of coffee. This study investigated the effect of water hardness and alkalinity on the sensory properties of brewed coffee (Colombian Kachalu) using duo-trio screening and descriptive sensory analyses. Coffees brewed with ultrapure water (UPW), used as the reference, were compared with brews prepared from UPW containing additions of calcium (Ca^{2 +}), magnesium (Mg^{2 +}), and bicarbonate (HCO₃ ^-), spanning from the lower levels found within the "ideal brewing zone," and up to higher experimental extremes designed to test the limits of their sensory impact. Across all sensory evaluations, water hardness alone produced no marked flavor changes, even when calcium was added at concentrations above those typically found in drinking water. In contrast, bicarbonate had a clear and pronounced effect on the sensory profile across the full tested range. Increasing bicarbonate levels, from brew-zone concentrations and up to the experimental extreme of 300 mg/L, substantially reduced perceived acidity, fruitiness, and complexity, while increasing roasted and bitter notes. Small differences observed in samples containing both calcium and bicarbonate were attributable to reductions in effective bicarbonate concentration due to calcium carbonate (CaCO₃) precipitation rather than to any direct flavor contribution from calcium. Overall, the findings indicate that, under the experimental conditions investigated, alkalinity, not hardness, was the primary determinant of sensory changes in brewed coffee. Maintaining appropriate bicarbonate levels is therefore essential for preserving desirable flavor attributes such as acidity and complexity, whereas variations in calcium within realistic ranges showed little sensory relevance. PRACTICAL APPLICATIONS: This study shows that bicarbonate levels in water, rather than water hardness, were the main factor shaping the sensory profile of the Colombian Kachalu coffee used in this study. Even small increases in bicarbonate made the coffee less acidic and fruity and more flat or bitter. These findings suggest that controlling alkalinity may be more important than adjusting hardness when designing water for coffee brewing. Consumers, cafés, and equipment manufacturers can use these findings to optimize water composition and improve flavor consistency across different brewing environments.