Mathematicians, physicists, and materials experts might not spring to mind as the first people to consult about whether you are brewing your coffee right. But a team of such researchers from around the globe — the United States, the United Kingdom, Ireland, Australia, and Switzerland — are challenging common espresso wisdom, finding that fewer coffee beans, ground more coarsely, are the key to a drink that is cheaper to make, more consistent from shot to shot, and just as strong.
Though lots of factors are involved, the norm for brewing an espresso shot is to grind a relatively large amount of coffee beans (~20 grams) almost as finely as possible. The fine grind, common sense goes, means more surface area exposed to the brewing liquid, which ought to boost extraction yield — the fraction of the ground coffee that actually dissolves and ends up in the final drink.
But when the researchers put together a mathematical model to explain the extraction yield based on the factors under a barista’s control — options such as the masses of water and dry coffee, the fineness or coarseness of the grounds, and the water pressure — and compared its predictions to brewing experiments, it became clear that the real relationship was more complicated. Grinding as finely as the industry standard clogged the coffee bed, reducing extraction yield, wasting raw material, and introducing variation in taste by sampling some grounds and missing others entirely.
Boosting the extraction yield through one or more of the routes illustrated by the model could also lead to economic gains for cafes and to sustainability benefits for the coffee industry as a whole. For example, at the current price of roasted coffee beans, dropping the mass of dry coffee from 20 grams to 15 grams per drink would add up to savings of a few thousand dollars per year for a small cafe, and $1.1 billion per year if scaled up to the whole US coffee industry. Being more efficient with coffee bean usage would also reduce waste at a time when coffee supply is under threat from changing climate in historic production areas.
Original article: Michael I. Cameron, Dechen Morisco, Daniel Hofstetter, Erol Uman, Justin Wilkinson, Zachary C. Kennedy, Sean A. Fontenot, William T. Lee, Christopher H. Hendon, Jamie M. Foster. Systematically Improving Espresso: Insights from Mathematical Modeling and Experiment. Matter, 2020; DOI: 10.1016/j.matt.2019.12.019