This physicist reveals why the way you stir your tea makes absolutely everything
At breakfast time or for a quick afternoon break, you make yourself a cup of coffee or tea, add a touch of sugar or milk, and stir. So far, nothing extraordinary. Yet, the way you stir your tea or coffee can make all the difference and produce completely different results!
The whirlpool, an ineffective... and noisy method!
As Julien Bobroff explains, King Charles of England (a leading figure in a country where tea time is a true institution) traditionally stirs his tea by making small, horizontal back-and-forth movements across the cup. Conversely, others stir the beverage by vigorously swirling the tea, creating a kind of vortex. These movements are not insignificant and produce different results! When you swirl the tea, "you give the liquid considerable speed and power. This creates a vortex in the tea or coffee, that is to say, a powerful and fairly stable top-to-bottom whirlpool," explains the scientist.
"The real problem arises when you want to stir in sugar," he continues. If you drop a sugar cube into the hot drink and stir in a circular motion with a spoon, you create a vortex that traps the sugar downwards. It won't be as well mixed and will logically dissolve less easily. Another drawback is that this movement causes splashing. The liquid risks overflowing and burning your fingers, explains the physicist. Furthermore, it makes noise because the spoon is constantly hitting the sides of the cup, which isn't very elegant!
The back-and-forth motion, the best way to stir your tea
A back-and-forth motion is much more delicate. You never touch the cup, and it's much quieter. That's how Charles III did it. The monarchy knows good manners! In short, if your goal is to dissolve the sugar thoroughly and minimize splashing while remaining as quiet as possible, you must use a back-and-forth motion with your spoon, and definitely not a swirling motion.
To go further
"It might seem trivial, but this question of mixing isn't just for show at teatime. It's a crucial issue in the chemical industry because you'll encounter the same problem when you want to mix two liquids so they react chemically," explains Julien Bobroff. The physicist goes on to explain that this is why some mixers use alternating or oscillating motions to ensure they never rotate in the same direction, resulting in an even better mix. QED!
