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Food Science


Coffee made with pew pew pew and illuminating what toilets spew

by Laura Howes
December 30, 2022 | A version of this story appeared in Volume 101, Issue 1


Cold pew pew pew

An illustration of a coffee maker reflecting green laser light.
Credit: Robin Braverman/Shutterstock/C&EN
Shine green for caffeine: Scientists make cold brew with green lasers.

Coffee—this Newscriptster gets through quite a lot of the stuff. The usual protocol for the aqueous extraction of caffeine and other organic compounds from coffee grounds involves heated water. But an alternative protocol has recently become increasingly popular: cold brew. In this method, budding baristas steep coffee grounds in cold water over a longer period (think hours rather than minutes). The result is usually less acidic and with a different flavor profile than coffee brewed with hot water.

But cold brew is not something someone can decide to make and enjoy immediately. While this home brewer can cope with a slower process as long as she gets herself organized, the times involved can be an annoyance. What if there were a way to perform a cold-brew extraction with hot-brew timescales? Researchers at the University of Duisburg-Essen led by Anna Rosa Ziefuß and her PhD supervisor Stephan Barcikowski have a solution. They brew it with lasers (npj Sci. Food 2022, DOI: 10.1038/s41538-022-00134-6). To be more precise, pulses of laser light centered at 532 nm—meaning green—are aimed at the coffee-and-water mix.

As well as being faster than cold brew (taking 3 min instead of hours and hours), the laser-based technique needs less coffee for the same amount of caffeine, making it more efficient. By analyzing the laser brew with mass spectrometry, the team showed that the laser-brewed coffee matched cold brew’s chemical profile much more than hot-brewed coffee did.

This was an in-lab experiment. Taste tests have yet to confirm the similarities using human analytical equipment. But Newscripts would be happy to volunteer for that job if the research continues. It’s incredible what lasers can brew.


What toilets spew, ew ew!

Laser light has many uses, of course. For example, the coherent beams are excellent for being scattered by particulates suspended in the air as well as in a coffee cup. At the University of Colorado Boulder, one research group that usually uses lasers to study fluid dynamics recently shined its lasers somewhere unappetizing—the toilet (Sci. Rep. 2022, DOI: 10.1038/s41598-022-24686-5). What the researchers found can’t be just flushed down the toilet. Not without putting the lid down first, at least.

A powerful green laser illuminates aerosol plumes from a toilet while it’s being flushed.
Credit: Patrick Campbell/University of Colorado Boulder
Full flush: Lasers let researchers image the plume leaping over a meter into the air.

While engineer John Crimaldi and coworkers aren’t the first to focus research on the toilet flush, the pictures from their experiments make their findings hard to ignore. For their study, the researchers decided to test a typical North American toilet as seen in public restrooms. They put a laser in front of it and connected multiple cameras to capture what happened next.

The laser created a sheet of laser light that illuminated a slice of air from the toilet bowl to nearly a meter above it. As the toilet flushed (with just clean tap water, no additions), that laser lit up all the water droplets that were ejected into the air. That illumination made it easy for the cameras to capture the plume’s size, velocity, and lifetime.

The team also used green lasers, so what’s here is a cloud of glowing green blobs of liquid leaping from the toilet bowl. Ew.

Plumes from flushing toilet bowls have been a concern for years, and the topic has gotten more attention during the COVID-19 pandemic. But the images and videos add a new, very visual understanding of the phenomenon, thanks to laser light. Newscripts will definitely be keeping the lid down whenever possible.

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