If you’re quite happy with a cup of instant – or worse still, prefer tea – we’ll be honest, this one’s probably not for you. But if you own coffee scales, can argue passionately about the importance of grind size, and time your espresso pull to the second, you may be interested to learn that a group of physicists believe they’ve optimized the process of making pour-over coffee.
Pour-over coffee is a brewing method that lots of javaphiles enjoy for its inexpensive equipment, versatility, and even the calming ritual it adds to their day. It’s a bit more hands-on than some methods, such as a French press, but much less expensive than a whole at-home espresso setup. Popular pour-over coffee makers you may have seen around include the Hario V60 and the Chemex.
But coffee itself, enjoyed by humans for thousands of years, is now under threat due to climate change. For the University of Pennsylvania scientists behind the new study, that was their motivation to find a way to get the best possible results from each bag of beans.
If you do know someone who makes pour-overs, or have tried it yourself, you’ve probably also seen the gooseneck water kettles that tend to come as part of the package. Coffee grounds are added to a damp filter in the pour-over maker, and – as the name suggests – water is poured over the top from the kettle. The brewed coffee then drips into the vessel below the maker.
It’s a simple enough procedure, but variations in any part of it can affect the end product.
“What we recommend is making the pour height as high as possible, while still maintaining a laminar flow, where the jet doesn’t break up when it impacts the coffee grinds,” said study author Ernest Park in a statement.
The key, according to physics, is in the strength of the water jet.
Image credit: Ernest Park
As it turns out, those long, curved necks on gooseneck kettles are perfect for this job. They produce a strong jet of water that creates what the team calls “an avalanche” within the coffee grounds. Grounds recirculate as the water seeps in, leading to effective mixing of water and grounds that you just can’t get with a thinner jet.
“If you have a thin jet, then it tends to break up into droplets. That’s what you want to avoid in these pour-overs, because that means the jet cannot mix the coffee grounds effectively,” explained author Margot Young.
The intrepid physicists took things a step further in their quest for pour-over perfection. As well as brewing a fair few cups of coffee, they mimicked the process using laser-illuminated particles in a transparent funnel to observe the effect of different water jets on the grains – much easier to visualize than dark-colored coffee grounds.
This study is the end of the caffeinated bean road for this particular team of physicists, whose research focus lies elsewhere. But it does highlight how many fascinating scientific discoveries could be lying in wait inside our very own homes.
“We can really learn something from both the chemistry and physics point of view by looking at the kitchen,” said author Arnold Mathijssen. “It leads to new science where you didn’t expect it.”
Once you’ve brewed your own coffee the science-approved way, why not try using it as a particle detector? And for more kitchen physics fun, ever tried sticking ice cubes in the microwave?
The study is published in the journal Physics of Fluids.
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