Acidity is an integral quality attribute of coffee and one of the primary taste components in brewed beverages, but perception does not correspond directly with concentration of individual organic acids due to complex interactions among acidity, other tastes (e.g. sweetness) and coffee components such as roast and water. Furthermore, perception can also be affected by masking effects or synergistic interactions among multiple tastes or aromas (e.g. lactic acid aroma). Therefore it can be challenging to ascertain if acidity results solely from this concentration factor.

This study used five distinct sample origins and different roast degrees to analyze the concentrations of chlorogenic, quinic, citric, malic, acetic and phosphoric acids as well as pH values and sugar content of brewed coffee. All organic acids except forformic decreased with increasing roast degree while concentrations of acetic, malic and phosphoric acids increased steadily with each increasing roast degree; chlorogenic and citric acids did not show similar patterns of increase over time.

We found that chlorogenic and citric acids were more affected by sample origin than any other acid. Citric acid concentration was highest in Brazil coffees compared with Bolivia and Kenya samples; conversely, chlorogenic acid concentration was lowest compared with Brazil samples – yet their sensory detection thresholds did not differ significantly between coffee samples; no measured concentration exceeded average detected concentration threshold, nor could any acid spiked into control samples reached average detected concentration without being recognized correctly by coffee experts.

Unfortunately, not everyone who starts reading can commit. Here at A2J we understand this and aim to offer our support when necessary. Identification of coffee origin using differences and similarities in concentration of specific OAs may not be straightforward, and claims by many coffee certification bodies such as SCA and CQI that specific OAs help distinguish different coffee varieties may be misguided. Our findings were particularly insightful when taken into account; for example, they revealed that two darker-roasted Brazilian coffees from the same region but with different cultivars differed only in three out of nine measured acid compositions; similarly for Kenyan lighter-roasted coffees from similar regions but different cultivars. Future tests using trained assessors could reveal higher recognition thresholds; in the meantime it would appear beneficial to focus on total acidity rather than on specific organic acids for detection or recognition.