Volume 2, Issue 3, 4 March 2020, Pages 631-648
Matter

Systematically Improving Espresso: Insights from Mathematical Modeling and Experiment

Michael I. Cameron 1 10, Dechen Morisco 1 10, Daniel Hofstetter 2, Erol Uman 3, Justin Wilkinson 4, Zachary C. Kennedy 5, Sean A. Fontenot 8, William T. Lee 6 7, Christopher H. Hendon 8 11, Jamie M. Foster 9

https://doi.org/10.1016/j.matt.2019.12.019

Highlights

• Development of a model for extraction of espresso
• Experimental observation of inhomogeneous extraction
• Optimization of espresso parameters to minimize coffee waste
• Implementation to yield monetary savings in a cafe setting

Progress and Potential
The modern coffee market aims to provide products which are both consistent and have desirable flavour characteristics. Espresso, one of the most widely consumed coffee beverage formats, is also the most susceptible to variation in quality. Yet, the origin of this inconsistency has traditionally, and incorrectly, been attributed to human variations. This study's mathematical model, paired with experiment, has elucidated that the grinder and water pressure play pivotal roles in achieving beverage reproducibility. We suggest novel brewing protocols that not only reduce beverage variation but also decrease the mass of coffee used per espresso by up to 25%. If widely implemented, this protocol will have significant economic impact and create a more sustainable coffee-consuming future.

Summary
Espresso is a beverage brewed using hot, high-pressure water forced through a bed of roasted coffee. Despite being one of the most widely consumed coffee formats, it is also the most susceptible to variation. We report a novel model, complimented by experiment, that is able to isolate the contributions of several brewing variables, thereby disentangling some of the sources of variation in espresso extraction. Under the key assumption of homogeneous flow through the coffee bed, a monotonic decrease in extraction yield with increasingly coarse grind settings is predicted. However, experimental measurements show a peak in the extraction yield versus grind setting relationship, with lower extraction yields at both very coarse and fine settings. This result strongly suggests that inhomogeneous flow is operative at fine grind settings, resulting in poor reproducibility and wasted raw material. With instruction from our model, we outline a procedure to eliminate these shortcomings.

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