For proper espresso, material scientists now suggest coarser grind and less coffee

Coffee is vitally important in my life. I consider myself fortunate that I have access to a truly amazing coffee roaster, that even in lockdown, has been keeping me supplied with freshly roasted and expertly sourced beans.

The key elements to all good coffee are good beans, proper roast, proper grind, good water, proper temperature, proper time for extraction.

Espresso is coffee, but elevated. With espresso comes the essential element of pressure, which transforms the water and coffee beans into a substance that has been studied in multiple peer-reviewed scientific studies over the years. (Seriously!)

A recent study published in Matter by Christopher Hendon and Michael Cameron focuses on the role that fluid dynamics plays in producing proper espresso. Here’s an excerpt:

I said, ‘Well hold on, there’s something physically strange happening here,’” Hendon said. “At the same time, we got started on the mathematical model, because I wanted to make sure that my sanity was intact and say that if I grind finer, I should expect higher extraction yield.”

What makes the model unique, and complicated, is its attention to detail. Senior author Jamie Foster said that the model captures the interactions between miniscule grounds of coffee, as well as the dynamics of the bed as a whole. Additionally, ground coffee comes in two sizes: boulders and fines. Too many fines can clog up the portafilter that extracts the espresso, yielding less coffee than expected.

The level of detail in the model and inclusion of pressure and espresso basket geometry distinguish this study from others that model coffee, Hendon said.

The findings seem to indicate that by using a slightly coarser grind than typically recommended for espresso, and a slightly leaner ratio of coffee to water, the results are measurably better.