The Science Behind Coffee Rings: A Tale of Evaporation and Particle Migration

Unraveling the Enigma of Coffee Rings: A Comprehensive Exploration of Their Formation

Coffee rings, those ubiquitous stains that adorn our cups and countertops, are more than mere aesthetic imperfections. They are fascinating physical phenomena that have captivated scientists for decades. This article delves into the intricate world of coffee rings, shedding light on their formation, the factors that influence their appearance, and their potential applications.

Coffee rings owe their existence to a combination of evaporation and particle migration. As a drop of coffee evaporates, liquid from the interior flows towards the edges to replenish the evaporating liquid. This flow carries along the suspended coffee particles, which accumulate at the perimeter of the drop. As evaporation continues, the coffee particles become increasingly concentrated, forming the characteristic ring-shaped stain.

The Role of Particle Shape: From Spheres to Oblongs

Traditionally, coffee rings were thought to form regardless of the shape of the suspended particles. However, recent research has revealed a surprising twist. Oblong particles, unlike their spherical counterparts, tend to clump together more strongly. This clumping hinders the flow of liquid from the drop’s center to the edge, resulting in a more even distribution of particles and a less pronounced ring effect.

Applications Beyond the Coffee Cup: From Inkjet Printing to Paint Formulation

The insights gained from studying coffee rings have far-reaching implications beyond the realm of spilled beverages. In the world of inkjet printing, manufacturers strive to prevent uneven drying of ink droplets, which can lead to smudging and poor print quality. By understanding the factors that influence coffee ring formation, researchers can develop inks with reduced solid content, potentially lowering production costs.

Similarly, in the paint industry, preventing uneven drying is crucial for achieving smooth, aesthetically pleasing finishes. The principles governing coffee ring formation can guide the design of paints that dry more evenly, eliminating the need for additional solvents and reducing environmental impact.

Conclusion: Coffee Rings as a Window into the World of Physics

Coffee rings, once dismissed as mere annoyances, have emerged as a valuable tool for understanding the interplay between evaporation, particle migration, and surface tension. The research surrounding coffee rings has not only deepened our appreciation for the hidden complexities of everyday phenomena but also provided practical insights with applications in diverse fields. From inkjet printing to paint formulation, the lessons learned from coffee rings continue to inspire innovation and advance our technological capabilities.

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  • 07 April 2021: This paper has been corrected and published at https://doi org/10. 1038/s41586-021-03444-z.
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We thank H. Li, X. Shi and M. Baildon for their early contributions to this project; J. Crocker, D. Grier and A. Marcus for providing their facilities, analysis code, and knowledge; and S Garoff, L. Mahadevan, S. Esipov, R. Leheny, D. Mueth, E. Ehrichs, J. Knight, S. Blanton, N. Menon, J. Cina and L. Kadanoff for discussions. This work was supported by the NSF-MRSEC, NSF and DOE.

  • Chicago, 60637, Illinois, USA; James Franck Institute, 5640 South Ellis Avenue, Robert D. Deegan, Olgica Bakajin, Greb Huber, Sidney R. Nagel & Thomas A. Witten.
  • University of Chicago, Department of Computer Science, 1100 East 58th Street, Chicago, 60637, Illinois, USATodd F Dupont.

Correspondence to Robert D. Deegan.

Deegan, R. , Bakajin, O. , Dupont, T. et al. Capillary flow as the reason behind dried liquid drop ring stains Nature 389, 827–829 (1997). https://doi. org/10. 1038/39827.

  • Received: 01 May 1997
  • Accepted: 26 August 1997
  • Issue Date: 23 October 1997
  • DOI:

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“There are a lot of very elegant physics in a lot of everyday objects,” Yunker told LiveScience. “There are also a lot of practical applications that come out of some very basic physics.”

“I think people are very surprised that by just changing the shape of the particles without changing the chemistry, were able to avoid this effect,” said University of Pennsylvania graduate student Peter Yunker, who led the research.

Each particle, or cluster of molecules, in the case of coffee is about a micrometer (one millionth of a meter) wide, making it roughly 10,000 times larger than individual coffee molecules, according to researchers.

Now researchers have discovered a surprising twist that changes our understanding of how these stains form. It turns out that liquids, such as coffee, that are made up of spherical particles dry differently than liquids with more oblong particles, scientists have found.

As a drop of coffee dries, liquid evaporates more efficiently from the drops thinner edges. Liquid in the middle then flows outward to replenish the edges, carrying the suspended solids with it. These are then left behind in a ring around the edges of the drop when all the water has evaporated, leaving the telltale dark halo at the drops edge, with a more translucent center to the stain.

The Coffee Ring Effect (and a little magic trick)


How do you stop the coffee-ring effect?

Suppression of CRE. CRE can be suppressed through one of the three physical strategies (i) preventing the pinning of the contact line; (ii) disturbing the capillary flow towards the contact line and (iii) preventing the particles being transported to the droplet edge by the capillary flows.

How do you prevent the coffee-ring effect?

The coffee-ring effect is impeded by triggering gelation of the coating materials via a thioacetate–disulfide transition which counterbalances the capillary forces induced by evaporation.

Why do coffee cups leave rings on table?

People often refer to this as “drinks sweating.” If the wood is exposed to this direct moisture, the moisture is pushed into the table by the glass resting there. The water is bound to get into the finish of the wood and leave behind that pesky mark.

What causes mug rings?

The coffee-ring pattern originates from the capillary flow induced by the evaporation of the drop: liquid evaporating from the edge is replenished by liquid from the interior. The resulting current can carry nearly all the dispersed material to the edge.

What causes coffee ring effect?

The shape of particles in the liquid is responsible for coffee ring effect. On porous substrates, the competition among infiltration, particle motion and evaporation of the solvent governs the final deposition morphology. The pH of the solution of the drop influences the final deposit pattern.

Does coffee cause ringing in the ears?

Coffee by itself does not cause ringing in the ears. Those people who do not have the habit of consuming coffee, may suffer some symptoms such as tachycardia or insomnia if they consume large amounts of caffeine. Tinnitus (persistent ringing in the ears) may have multiple causes and should be treated by a specialist.

Why do coffee stains form a ring?

Because the particles stay in the same place instead of moving inward as the volume of coffee shrinks, the perimeter of the stain stays in tact, forming a ring. Not entirely satisfied with this explanation, another group of scientists continued to explore the effect.

Why does coffee have a dense ring?

In the science journal “Nature,” physicists published a study on the way particles move in a drop of liquid. The particles in coffee, they found, move to the perimeter of the drop, which is why a dense ring forms after evaporation.

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