Spilling coffee is not the best experience. It might be hot or it might run down a business suit just before a key meeting. The risk is lowered if there is a bit of foam on the top of the coffee. This means that the latte is somewhat safe than the espresso or the regular milky coffee.
A latte (or, more precisely a caffè latte) is a a coffee drink made with espresso and steamed milk, with an added layer of foamed milk. It is a popular offering at many coffee shops.
In terms of the effects when coffee is spilled, researchers have discovered that a few layers of milky bubbles have the effect of suppressing the sloshing motion of liquids. This means when someone is making a precarious walk carrying coffee, if the coffee has a foam layer the chance of the coffee swishing out is much lower.
To research the fluid dynamics, Lab Manager magazine notes that the scientists constructed a machine made up of a narrow rectangular container built from of glass. The chamber was filled with a solution of water, glycerol and a dishwashing detergent. The researchers then injected air at a constant flow rate through a needle located at the bottom of the rectangular cell. Through this process the scientists created uniform layers of 3-millimeter-diameter bubbles.
In reviewing the outcome, the researchers are of the view that the foam dissipates the energy of the moving liquid through friction with the sides of the container.
The research is of far greater value than simply warning java lovers. This includes the safe transport of liquefied gas, as might occur with in trucks, or propellants used in rocket engines.
The study into the fluids of coffee took place at the French National Center for Scientific Research (CNRS). The research has been reported to the journal Physics of Fluids and the paper is titled “Damping of liquid sloshing by foams.”