The secret to brewing the perfect cup of espresso


Caffeine fans have been attempting to pull the perfect espresso for decades. And a group of mathematicians and scientists around the globe came to the conclusion that the skill and precision needed to create that flawless espresso involves just one thing: grinding fewer coffee beans, more coarsely.

If done this way, the result turns out to be more consistent from shot to shot, just as strong as a conventional espresso, and, interestingly, cheaper to make.

The researchers’ – from the US, UK, Ireland, Australia and Switzerland – formula is contesting the standard method of most people in the coffee industry, who use fine-grind settings and plenty of coffee beans to get a mix of bitterness and acidity. This method is “unpredictable and irreproducible”, says co-senior author Christopher Hendon, a computational chemist at the University of Oregon.

"It sounds counterintuitive, but experiments and modelling suggest that efficient, reproducible shots can be achieved by simply using less coffee and grinding it more coarsely," he said. Their research was published in the journal Matter.

The norm vs. scientists’ method

While several factors make up the more conventional way of brewing an espresso, the researchers explain that the most popular way is grinding a large amount of coffee beans as finely as possible. The logical reasoning behind this is that the finely ground beans ultimately means more surface area exposed to the brewing liquid which boosts extraction yield (the amount of ground coffee that eventually dissolves, ending up in the drink).

However, after comparing their predictions with brewing experiments, the researchers argued that fine grinding, according to the industry standard, clogged the coffee bed, causing a reduction in extraction yield. They also found that this technique wastes raw material and leads to variation in taste.

Less is more

"One way to optimise 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 said.

Considering that the water flows under pressure through a mass of millions of individual coffee grains of different shapes and sizes, developing a coffee extraction model was no easy task – but the scientists drew on electrochemistry for their predictions.

What this means for the coffee industry

By boosting the extraction yield, cafés could benefit economically and ensure sustainability, the researchers said. They explain that at the current price of roasted coffee beans of 20 grams per drink, reducing it to 15 grams would lead to a whopping saving of a few thousand dollars per year for a small café. If looking at the whole US coffee industry, this would amount to $1.1 billion per year.

Even more reason to be more efficient with coffee bean usage is that a reduction in waste also means acting ethically and sparing the planet. A 2019 study published in Science Advances notes that 60% of wild coffee species are under threat of extinction.

Forbes reports that the majority of the wild coffee species are found in Africa and Madagascar, and that a triple threat of deforestation, human encroachment and disease in these areas is increasingly killing wild coffee plants. 

Image: Mike Kenneally, Unsplash

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