Researchers Pore Over the Physics Behind the Layered Latte

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The layered latte isn't the most widely known espresso drink on coffee-shop menus, but it is a scientific curiosity. Instead of a traditional latte, where steamed milk is poured into a shot (or several) of espresso, the layered latte is made by pouring the espresso into a glass of hot milk. The result is an Instagram-friendly drink that features a gradient of milky coffee colors from pure white on the bottom to dark brown on the top. The effect is odd enough that Princeton University researchers decided to explore the fluid dynamics that make it happen, as The New York Times reports.

In a new study in Nature Communications, Princeton engineering professor Howard Stone and his team explore just what creates the distinct horizontal layers pattern of layered latte. To find out, they injected warm, dyed water into a tank filled with warm salt water, mimicking the process of pouring low-density espresso into higher-density steamed milk.

Xue et al., Nature Communications (2017)

According to the study, the layered look of the latte forms over the course of minutes, and can last for "tens of minutes, or even several hours" if the drink isn't stirred. When the espresso-like dyed water was injected into the salt brine, the downward jet of the dyed water floated up to the top of the tank, because the buoyant force of the low-density liquid encountering the higher-density brine forced it upward. The layers become more visible when the hot drink cools down.

The New York Times explains it succinctly:

When the liquids try to mix, layered patterns form as gradients in temperature cause a portion of the liquid to heat up, become lighter and rise, while another, denser portion sinks. This gives rise to convection cells that trap mixtures of similar densities within layers.

This structure can withstand gentle movement, such as a light stirring or sipping, and can stay stable for as long as a day or more. The layers don't disappear until the liquids cool down to room temperature.

But before you go trying to experiment with layering your own lattes, know that it can be trickier than the study—which refers to the process as "haphazardly pouring espresso into a glass of warm milk"—makes it sound. You may need to experiment several times with the speed and height of your pour and the ratio of espresso to milk before you get the look just right.

[h/t The New York Times]

Amazon's Under-the-Radar Coupon Page Features Deals on Home Goods, Electronics, and Groceries

Stock Catalog, Flickr // CC BY 2.0
Stock Catalog, Flickr // CC BY 2.0

This article contains affiliate links to products selected by our editors. Mental Floss may receive a commission for purchases made through these links.

Now that Prime Day is over, and with Black Friday and Cyber Monday still a few weeks away, online deals may seem harder to come by. And while it can be a hassle to scour the internet for promo codes, buy-one-get-one deals, and flash sales, Amazon actually has an extensive coupon page you might not know about that features deals to look through every day.

As pointed out by People, the coupon page breaks deals down by categories, like electronics, home & kitchen, and groceries (the coupons even work with SNAP benefits). Since most of the deals revolve around the essentials, it's easy to stock up on items like Cottonelle toilet paper, Tide Pods, Cascade dishwasher detergent, and a 50 pack of surgical masks whenever you're running low.

But the low prices don't just stop at necessities. If you’re looking for the best deal on headphones, all you have to do is go to the electronics coupon page and it will bring up a deal on these COWIN E7 PRO noise-canceling headphones, which are now $80, thanks to a $10 coupon you could have missed.

Alternatively, if you are looking for deals on specific brands, you can search for their coupons from the page. So if you've had your eye on the Homall S-Racer gaming chair, you’ll find there's currently a coupon that saves you 5 percent, thanks to a simple search.

To discover all the deals you have been missing out on, head over to the Amazon Coupons page.

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Late MythBusters Star Grant Imahara Honored With New STEAM Foundation

Grant Imahara attends San Diego Comic-Con
Grant Imahara attends San Diego Comic-Con
Genevieve via Flickr // CC BY 2.0

Fans of MythBusters and White Rabbit Project host Grant Imahara were saddened to hear of his passing due to a brain aneurysm in July 2020 at the age of 49. Imahara, a graduate of the University of Southern California, used the television medium to share his love of science and engineering. Now, his passion for education will continue via an educational foundation developed in his name.

The Grant Imahara STEAM Foundation was announced Thursday, October 23, 2020 by family and friends on what would have been Imahara’s 50th birthday. The Foundation will provide mentorships, grants, and scholarships that will allow students from diverse backgrounds access to STEAM education, which places an emphasis on science, technology, engineering, arts, and math. (Formerly referred to as STEM, the “A” for art was added more recently.)

Imahara had a history of aiding students. While working at Industrial Light and Magic in the early 2000s, he mentored the robotics team at Richmond High School to prepare for the international FIRST Robotics Competition. Whether he was working on television or behind-the-scenes on movies like the Star Wars prequels and The Matrix sequels, Imahara always found time to promote and encourage young engineering talent.

The Grant Imahara STEAM Foundation’s founding board members include Imahara’s mother, Carolyn Imahara, and close friends Don Bies, Anna Bies, Edward Chin, Fon H. Davis, Coya Elliott, and Ioanna Stergiades.

“There are many students, like my son Grant, who need the balance of the technical and the creative, and this is what STEAM is all about,” Carolyn Imahara said in a statement. “I’m so proud of my son’s career, but I’m equally proud of the work he did mentoring students. He would be thrilled that we plan to continue this, plus much more, through The Grant Imahara STEAM Foundation.”

Imahara friend Wade Bick is also launching an effort in concert with the USC Viterbi School of Engineering to name a study lounge after Imahara. Donations can be made here.

You can find out more about the foundation, and make a donation, on its website.