Wednesday, February 04, 2009

"Your drink looks like it's alive!"

During lunch the other day, a coworker at a neighboring table asked me about my drink: "What is that? It looks like it's alive!" It wasn't alive, it was just a glass of sparkling water with a spoonful of Korean yuja cha (citron-honey preserve) at the bottom.

What made it look alive was bubbles of carbon dioxide that carried the fruit from the bottom to the top. At the top, the bubble either popped, detached from the fruit, or reduced in size, causing the fruit to sink back to the bottom. It was almost like a lava lamp (though in this case the forces driving the motion are chemical and physical, not thermal).

In this first video (10 seconds long), a piece of fruit on right side of the glass bobs up and down.

video

In the second video (15 seconds long), a few pieces of fruit move up and down while a group of bubbles try in vain to carry a large piece of pulp to the surface.

video

Here's what I think is happening: sparkling water is a solution of carbon dioxide (CO2) dissolved in water. The concentration of CO2 in the water is higher than what would be allowed at atmospheric pressure, so some of the CO2 comes out of solution as bubbles, which are buoyant and rise to the surface. In situations like these, bubbles tend to form on scratches and other inhomogeneous places that are called "nucleation sites" in technical lingo (the ability of roughness to cause bubbles is why some sparkling wine glasses are artificially roughened at the bottom of the glass). In my drink, the fruit pieces provide these "nucleation sites." Sometimes a piece of fruit spawns enough bubbles to make it float to the top of the liquid.

It took me a few tries to get these short, low-quality videos (using my Canon Powershot SD600 and a strangely ornery Picasa 3 that never seemed to do what it was supposed to do). As I crouched next to my counter, waiting for the bubbles to do their thing, it made me think of the rigors of nature photography, where the camera operator might sit in a tree for days, tormented by insects, buffeted by rain and wind, punished by the heat, waiting for a bird to do its courtship dance, a rare rodent to leave its nest, or some other rare occurrence, just to get a few minutes of footage. I'm grateful that there are such dedicated people out there to bring the magic of nature to our DVD players. The bonus features in "Life of Mammals" and "Life in the Undergrowth" have some stories about the trials the job of a documentary camera operator, including a harrowing tale of filming in a cave with thousands (or was it millions?) of bats, a floor covered with untold amounts of their droppings, an atmosphere rich in noxious gases, and all sorts of creepy-crawlies.




Random link from the archive: Snacks for the Ears

Technorati tags: Food : Drinks

1 comment:

Meg D said...

We used to do the same thing in the college cafeteria with a few raisins dropped into glasses of Mountain Dew or Sprite. Highly entertaining!