Coffee extraction kinetics

Do you remember being told in one of the first barista skills classes you did that we grind coffee evenly so that it extracts evenly? Well this is not entirely true.

The flavour and taste of a coffee beverage is the result of a complex relationship between volatile and non-volatile compounds. The extraction of those components is affected by the quality of the green coffee beans, combined with the roasting profile and extraction parameters.

The grinding step is one of the most critical parameters, depending on the roasting profile and the accuracy of the grinder machine. During the coffee extraction, the water percolation must pass through the coffee bed, distributed in inter-granular (within the grain) and intra-granular (between the grains) pores. Therefore, the compounds are extracted from the surface of particles and from within their pores. Bigger particles will allow the extraction from the kernels, which is slower than the extraction from the surface.

The result in our cup of coffee is determined by the balance between a fast extraction from the ground coffee’s surfaces and slow diffusion of compounds in the large particle kernels. Your grinder determines the size, shape and distribution of particle sizes of the ground coffee. The degree of roast determines the density and brittleness. The brewing recipe and method can manipulate the rate of extraction.

Next time you enjoy a coffee, think about the extraction level, is it balanced, was there something more that could be gained from a different roast profile or the brew recipe?

Find out more about this subject by joining our upcoming course Coffee Extraction Kinetics, which discusses the physicochemical parameters that can influence coffee extraction.