Scientists Say We're Making Espresso Wrong (and They May Be Right)

It's easy to understand the appeal of those pod-based coffee machines: Pop in a pod, press a button and done. But many of us prefer the opposite end of the effort spectrum: Choose a roaster, choose beans, choose a brewing method, choose a grind, choose a water temperature, choose a ratio of water to beans, choose a brewing time, and… I think that's it? However, with multiple variables involved, getting it right on a consistent basis can be frustrating.

Now, things may be complicated even further for espresso fans: A new study suggests that the conventional method for making espresso may be problematically inconsistent, and some of those aforementioned variables should probably be reconsidered from the ground—or grounds—up.

In the study "Systematically Improving Espresso: Insights from Mathematical Modeling and Experiment," published this week in the journal Matter, a global team of researchers from the United States, the United Kingdom, Ireland, Australia, and Switzerland have concluded that the key to consistent results—with less cost and waste—might be to make espresso with fewer beans and a coarser grind.

"Most people in the coffee industry are using fine-grind settings and lots of coffee beans to get a mix of bitterness and sour acidity that is unpredictable and irreproducible," co-senior author Christopher Hendon, a computational chemist at the University of Oregon, explained in a statement. "It sounds counterintuitive, but experiments and modeling suggest that efficient, reproducible shots can be accessed by simply using less coffee and grinding it more coarsely."

In essence, the current method for making espresso is a crapshoot. No, you won't crap out entirely: You'll still get a drinkable brew. However, speaking over the phone, Hendon explained to me that conventional brewing includes enough inevitable variability that the flavor of your shot won't be the same every time. Fine grinds tend to pack together in the bed, and as water follows the path of least resistance through them, some grinds get higher extraction rates while others are barely extracted at all. As a result, espresso shots are usually an average of extreme variation, not a consistent whole.

Figuring out how to get consistent results from millions of coffee grinds isn't easy. "You would need more computing power than Google has to accurately solve the physics and transport equations of brewing on a geometry as intricate as a coffee bed," co-senior author Jamie M. Foster, a mathematician at the University of Portsmouth in the United Kingdom, added in the study's announcement.

Luckily for the ten-person research team, though not quite Google, they were able to mathematically analyze the brewing process—getting some help from electrochemistry—then compare their models to the actual results. After making tweaks across thousands of shots, they determined the best way to achieve that previously elusive consistency: "One way to optimize extraction and achieve reproducibility is to grind coarser and use a little less water, while another is to simply reduce the mass of coffee," Hendon stated.

But what does a group of "mathematicians, physicists, and materials experts" (as the press release states) know about good tasting coffee anyway? Hendon told me a number of members in the group are coffee experts as well, but that's kind of beside the point. His convincing argument: Let's make the process of brewing espresso consistent and then make adjustments for flavor from there. Currently, baristas are metaphorically throwing darts at a moving board: Even if you like the flavor you're getting, there's little guarantee it will be the same the next time. Hendon seemed confident that, with his team's method, baristas could work their way back to the flavor profile they prefer—and then reproduce it more often.

The coffee expert I spoke to, Charles Babinski, co-founder of the Los Angeles-based coffee company Go Get Em Tiger, didn't necessarily disagree. "I follow the adage to be wary of any coffee science article that makes its way into popular media," he told me via email. "I have nothing but love and respect for Hendon, and my layman's view of his (obviously rather technical) paper is that it mostly checks out with my experiences. I have definitely witnessed lower doses and courser grounds yield comparable/better extractions than shots done within current industry best practices."

Babinski did have one bone to pick, however. "In my experience, the faster shots that Hendon and co. are describing are just not as expressive or exemplary as a 'well-extracted' longer shot," he explains. "They cover this somewhat in the paper…. I also don't think that anything they said in the paper particularly refutes my current viewpoint since the focus is on efficiency and repeatability, not quality, so I think this data could definitely be used to progress toward new approaches to coffee extraction."

Meanwhile, all this talk of taste doesn't even include the study's other big benefit: Using fewer beans costs less and creates less waste, improving sustainability. The researchers suggest a small café could save thousands while the entire U.S. coffee industry could save as much as $1.1 billion. (Or they could pass some of those savings on to us!)

But in the end, Hendon stressed that he agrees taste is king, and he's not trying to mess with that. "There is a tremendous dependency on the preferences of the person producing the coffee," he stated; "we are elucidating the variables that they need to consider if they want to better navigate the parameter space of brewing espresso." Unless, of course, you like playing craps? The highs can certainly be thrilling as long as you can handle the lows.