Don Iszatt has been researching the process of coffee solids extraction across a range of espresso brew methods. Originating at Finca Coffee Roasters, he describes the origins of his study, “We wanted to take an empirical look at extraction, and found a mathematical function that describes the rate of extraction”.
Measured as a percentage of the total weight of the dry coffee and labeled the “yield”, it designates the amount of solids dissolved in the liquid of the coffee. During the initial stages of the brew the yield tends to be higher, and typically decreases as the extraction proceeds, as the extracted solids are less likely to dissolve.
During the experiment, separate espresso shot extractions were stopped at different points, so that the mass of the espresso collected and the amount of solids dissolved could be measured. One calculates the resulting espresso yield to plot its relationship to the mass. The analysis of the data can be expressed as a power function, where yield Y = 3.9 M ^ 0.45, for the mass M. Don Iszatt named this function the Espresso Power Curve (EPC).
