The prices of arabica beans, the essence of coffee, have skyrocketed in recent years due to unfavorable weather conditions. Physicists are exploring whether better extraction could reduce the amount of coffee needed without compromising quality.
To measure the impact of variables on taste, the team recorded the temperature, weight, grind size, and extraction time of each brew.
Credit: Ernest Park
Researchers at the University of Pennsylvania studied fluid dynamics during coffee brewing. Their goal was to optimize flavor extraction while using fewer beans. The team combined precise measurements and high-speed analyses to observe movements invisible to the naked eye.
The study, published in
Physics of Fluids, reveals that the pouring height of water influences extraction efficiency. A stream of water poured from a certain height creates 'miniature avalanches' that better mix the beans with the water. This increased agitation allows for more flavor extraction with less coffee.
Scientists replaced coffee with transparent silica gel particles to visualize the process. A laser and high-speed camera captured water penetration into the particle bed. These observations showed that laminar flow, achieved with a gooseneck kettle, optimizes extraction.
Experiments with real coffee beans confirmed that pouring height affects coffee strength. A thicker stream poured from higher up produces stronger coffee, while a finer stream maintains extraction independent of height.
In Arnold Mathijssen's lab, researchers used a gooseneck kettle, coffee grinder, and filtration method to study fluid dynamics during brewing.
Credit: Ernest Park The implications of this research extend beyond the kitchen. The discovered principles apply to rock erosion under waterfalls or wastewater treatment. Studying coffee thus opens perspectives on complex natural and industrial phenomena.
The team continues to explore these fluid dynamics in other contexts, such as cleaning biofilms on medical devices. This research illustrates how seemingly simple studies can reveal universal mechanisms.
How does pouring height influence coffee extraction?
The height at which water is poured over coffee beans plays a crucial role in flavor extraction. A stream poured from a certain height creates enough agitation to efficiently mix water and beans, increasing their contact surface.
This effect, called a 'miniature avalanche,' results from the kinetic energy of the water stream. When water falls from sufficient height, it penetrates deeper into the coffee bed, leading to more uniform and complete extraction of aromatic compounds.
However, pouring water from too high can have the opposite effect. The stream breaks into droplets, introducing air into the mix and reducing extraction efficiency. Finding the right balance is therefore essential to optimize the process.
This discovery shows that simple adjustments in brewing technique can significantly improve coffee quality while reducing the amount of beans needed.
What is laminar flow, and why is it important for coffee?
Laminar flow refers to smooth fluid movement where particles move in parallel layers without turbulent mixing. Laminar flow allows water to pass evenly through the coffee bed, maximizing flavor extraction.
A gooseneck kettle is often used to achieve this flow. Its narrow, elongated spout allows precise control of the water stream's direction and speed, promoting optimal contact between water and coffee grounds.
Conversely, turbulent flow, caused by irregular or too-fast pouring, can lead to uneven extraction. Some parts of the coffee will be over-extracted, tasting bitter, while others will be under-extracted, lacking flavor.
Understanding and mastering laminar flow is therefore essential for preparing consistently high-quality coffee while conserving precious arabica beans.