Researcher have shown there is a definitive, scientifically proven technique you can use to give your latte macchiato a beautiful textured look.
Very quickly pouring the espresso into milk can create this textured look, US researchers have found.
They weren’t interested in the best methods to make coffee-based drinks, but in the physics behind producing layered structures in soft materials.
The researchers, from the Department of Mechanical and Aerospace Engineering at Princeton University, used dyed water and a salt solution to mimic a latte macchiato.
A barista will generally make one by slowly pouring the espresso into the milk: The colder, denser milk forms the lower layer while the espresso occupies the middle under the light milk foam on top.
In their paper published by the London-based journal Nature Communications, the researchers identify “double-diffusive convection” as the mechanism causing the layering, such as occurs in the ocean due to temperature and salinity differences.
The downward jet of espresso is pushed back upwards by the denser milk, forming a mixture over the milk at the bottom, they note. At low injection speeds, the mixture remains unchanged as it cools to room temperature.
Above 21m per second, though, the espresso penetrates deeper, increasing the mixture’s thickness.
The liquid closest to the wall of the glass cools, becomes denser and sinks until it reaches a layer of equal density, at which point it starts to circulate horizontally – forming distinct layers within several minutes.
“This single-step, single-chemistry method can facilitate the fabrication of multiple-layered structures in food science, tissue engineering and other applications in materials science,” the researchers write. – dpa
This is the way it's normally done, by pouring the espresso slowly into the milk.