No-spill latte

Rivalries abound in human consciousness and history. The houses of York and Lancaster irritated each other so intensely that they could only settle their differences with a series of wars (and war is still war even if you name it after a flower…a rose by any other name…). Countless national antagonisms have characterised humanity throughout the centuries and millennia and they can express themselves today in contests like the “The Ashes” (between Australia and New Zealand). On a more mundane, but no less fiery, level we divide ourselves into rival camps over the choices we make daily. There is fierce bemusement between urban SUV drivers and those of more reasonably proportioned vehicles. Then there is the simmering disquiet over our diets, here is a recipe for passionate discussion: add one omnivore, one paleo advocate, and one vegan to a small room, simmer at room temperature for ten minutes, season with menu options, and watch the discussion rise. Tea and coffee drinkers too have maintained a quiet but tangible dissension across the muffin table. Even within coffee drinking ranks there murmurings too; macchiato drinkers look with aloof disdain at long black drinkers who in turn show rough contempt for latté sippers and everyone holds condescension for those who favour an instant brew. Now a new study adds to the coffee drinking discussion by giving latté drinkers some ammunition as it seems a latté is less likely to spill.

No, it is not that latté drinkers are especially careful of their precious beverage or even that long black consumers are more apt to be clumsy; it is the nature of the latté itself that makes it less likely to spill.

The researchers began their study prompted by instrictions from a coffee shop that a takeaway latté probably would not need a lid and the similar observation that Guiness, a heavily foamed beer, is less likely to slop out of its glass than other beers on the way to the table. Based on these arduous preliminary studies the researchers supposed that foam on top of a liquid makes it more stable.

To test this they used a narrow rectangular glass container that they filled with a solution of water, glycerine, and dishwashing liquid. By injecting air at a constant flow rate through a needle located at the bottom of the container the researchers created uniform layers of 3mm diameter bubbles. They then experimented with jolting movements to the container or rocking it steadily back and forth.

They found that just five layers of foam were enough to decrease waves by a factor of 10 which of course translates into much less spill. More than five layers of foam don’t have a much greater protective effect, but the foam does dissipate the energy of the sloshing liquid through friction with the sides of the container.

The researchers say this could have implications for transport of things like liquid gas in tankers where a foam may dissipate the friction of the gas on the walls of the tanker. This may well be true but in the Wars of the Bean the true gravitas of this finding lies in the hands of latté drinkers who will know have another reason to say, “I told you so”.