Coffee extraction: A review of parameters and their influence on the physicochemical characteristics and flavour of coffee brews

The physicochemical characteristics and flavour of coffee are related to the volatile and non-volatile compounds produced during roasting, which reach the coffee cup upon brewing. This review focuses on interpreting the contribution that various parameters have during the coffee extraction process (coffee brewing). Coffee brewing methods and their extraction parameters were analysed in terms of phenomenological explanations and their effect on the physicochemical and flavour characteristics of brewed coffee. Many brewing methods have been developed to achieve a myriad of coffee flavour characteristics. Although several well-known brewing techniques have been adopted in the coffee industry, little associated relevant scientific data is available. Overall, these methods vary by extraction pressure, coffee/water ratio, water quality, contact time, particle size distribution, and temperature. An overview shows that all these factors modify the extraction of bioactive and volatile compounds that affect the flavour profile of the beverage. However, more in-depth explanation of the mass and energy transport phenomena would be useful to improve the understanding of the relationship between extraction variables and coffee flavour. Thus, phenomenological explanations are included to impart a better understanding of physicochemical and flavour changes in coffee beverages. Additionally, several gaps in knowledge relating to the extraction process are identified; and new trends in coffee extraction, including the cold brew method, are also discussed.