Modelling of coffee extraction during brewing using multiscale methods: An experimentally validated model

Abstract

Accurate and repeatable extraction of solubles from roasted and ground coffee with hot water is vital to produce consistently high quality coffee in a variety of brewing techniques. Despite this, there is an absence in the literature of an experimentally validated model of the physics of coffee extraction. In this work, coffee extraction from a coffee bed is modelled using a double porosity model, including the dissolution and transport of coffee. Coffee extraction experiments by hot water at 90°C were conducted in two situations: in a well stirred dilute suspension of coffee grains, and in a packed coffee bed. Motivated by experiment, extraction of coffee from the coffee grains is modelled via two mechanisms: an initial rapid extraction from damaged cells on the grain surface, followed by a slower extraction from intact cells in the grain kernel. Using volume averaging techniques, a macroscopic model of coffee extraction is developed. This model is parameterised by experimentally measured coffee bed properties. It is shown that this model can quantitatively reproduce the experimentally measured extraction profiles. The reported model can be easily adapted to describe extraction of coffee in some standard coffee brewing methods and may be useful to inform the design of future drip filter machines.