Any good barista will let you know that if you wish to make a pleasant latte you pour milk into the espresso — not the opposite method round.
However there’s one other model of latte on the market, too — the layered latte, or #layeredlatte as you’ll discover on Instagram. Created by chance, or by baristas experimenting with new drinks, these striped drinks begin with a glass of heated milk after which pour within the espresso. They’re not as fairly or in style as a unicorn Frappuccino or a rainbow latte, however they’ve their very own allure.
Bob Fankhauser, a retired engineer in Portland, Ore., unintentionally created his personal layered latte at house and wished to know why these fairly layers kind. “It’s a very intriguing phenomenon,” stated Mr. Fankhauser. “There’s no apparent purpose that the liquid ought to manage itself into totally different density layers.”
Final 12 months, Mr. Fankhauser despatched an e-mail together with pictures of his unintentional layered lattes to Howard Stone, a chemical engineer who research fluid dynamics at Princeton College and impressed him and a graduate pupil to check this out. The workforce revealed their outcomes Tuesday in Nature Communications. Anybody can do that at house, however cooks creating layered jellies or bioengineers creating artificial human tissues could discover this one-step course of helpful, they instructed.
After recreating the latte with their very own espresso and milk, the workforce created a simulated espresso drink, injecting heated, dyed freshwater into heated, denser saltwater to check the scientific parameters that make this spontaneous layering potential. Pouring scorching espresso into heat milk at a sure velocity, they discovered, induced an interplay between temperature and density that brought about the drink to separate into layers of various densities.
The identical primary phenomenon, known as double-diffusive convection, creates layers of water within the ocean. There, water containing totally different quantities of salt has totally different densities, identical to espresso and denser milk in a latte. When the liquids attempt to combine, layered patterns kind as gradients in temperature trigger a portion of the liquid to warmth up, turn into lighter and rise, whereas one other, denser portion sinks. This provides rise to convection cells that entice mixtures of comparable densities inside layers.
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