How Come?

Archive for the ‘food’ Category

How come it’s so hard to break a piece of dry spaghetti in two?  Why does it break into more pieces?  Also, when you slurp up a strand of cooked spaghetti, why does the pasta sauce fly off?  asks a reader.

Spaghetti cooking

Before you is a pile of dry spaghetti.  Your job, should you decide to accept it, is to break each piece in half, so that the pasta fits easily into a small saucepan.  Ready, set, snap…Oops.  What should be a snap is actually frustratingly difficult, as tiny, broken bits of pasta litter the table.

Scientists tried to solve the broken pasta problem for years.  Most famously, the late physicist (and Nobel Prize winner) Richard Feynman spent an evening with friend (and supercomputer expert) W. Daniel Hillis, snapping spaghetti.  At the end of the night, there was a pile of broken spaghetti, but no satisfying theory.

But in 2005, two physicists in Paris may have solved the spaghetti puzzle.  The scientists took high-speed images of breaking spaghetti, and applied a mathematical equation describing how waves travel through a stressed object.  What they found:  As a piece of spaghetti is bent until it can curve no longer, it breaks.  The sudden release causes a burst of “flexural waves” to travel through the remaining pieces, causing them to curve sharply, too — leading to more breaking.

So in a split second, your pasta breaks into three or four pieces, instead of neatly in two.  (Watch dry spaghetti bend and fragment at www.youtube.com/watch?v=8GutricnMNc.)

Once you’ve cooked your broken (or intact) spaghetti and added sauce, you may be in the mood for slurping.  But while it’s fun to hoover up strands of spaghetti,  you could find the tablecloth–and everyone around you–covered in a fine spray of crushed tomatoes.

How come?  According to physicist Jearl Walker, of Cleveland State University, the culprit is…wait for it…the Spaghetti Effect.  It turns out that the Spaghetti Effect doesn’t just apply to pasta drawn into your mouth, but also to paper, metal, and other materials pulled into machinery.

Walker says that when a spaghetti strand is lifted from your plate, it already has some sideways swinging motion.  As you suck up the spaghetti, you leave less and less of the strand hanging free.  So the energy of motion–the kinetic energy of the strand — is concentrated in a smaller and smaller piece of strand.  Just before the strand disappears into your mouth, its sideways motion becomes violent enough to fling sauce across the table.

You can also see the Spaghetti Effect in action between meals, whenever you use the vacuum cleaner.  After you’re finished sweeping the living room, unplug the vacuum and press the cord rewind button.  As the spaghetti-like cord is sucked quickly into the base, it may begin to whip around, turning the metal-tipped plug into a moving hazard.  The solution:  Retract the cord slowly, with several gentle pushes of the button.  (And if you must slurp pasta, try to do it in slow motion.)

How come when you put sugar into boiling water, it fizzes?  asks Edward Drosse, of Smithtown, NY.

Ever add sugar to a cup of microwaved tea, only to have the tea (startlingly) boil over?  Boiling depends on bubbles, and sugar can make hot water more bubbly.

Boiling is evaporation, but fast and furious.  We can actually see the water leaving, as a cloud of steam.  It can take days for a room-temperature glass of water to evaporate, but a small pan of water can boil away in a matter of minutes.  That’s because when water reaches its boiling temperature (212 F. at sea level), it evaporates not just from the surface, but from deep within.

Adding sugar (or other ingredients, like salt) can make extremely hot water boil, or cause already-boiling water to boil faster.  How come?  Boiling begins with bubbles.  The first bubbles to appear on the walls of a heating pan of water are actually air that was dissolved in the water, re-emerging as a gas.  But as the bottom of the pan gets hot, liquid water itself begins to turn to gas.

Water begins forming vapor bubbles at hot spots here and there on the pan bottom.  Steam bubbles form most easily on a rough, uneven surface.  Tiny crevices are ideal “nucleation sites,” places where bubbles can get a foothold and grow.

When steam bubbles inflate, break free, and begin to rise, their journey is short-lived.  As a bubble floats up into cooler water in the middle of the pan, it collapses like a deflated balloon.  Why?  At lower temperatures, a bubble’s pressure drops, allowing the kitchen air — the local part of the Earth’s atmosphere — to crush it.

But when the water’s temperature reaches the boiling point throughout, the pressure in the vapor bubbles increases to that of the air.  Bubbles from down under can then rise to the surface.  Where, with tiny pops, they release their vapor into the air.

When you drop sugar (or salt, or powdered sweetener) into boiling water, the crystals provide a raft of new nucleation spots.  Presto–a crowd of new vapor bubbles forms, creating a short-lived fizzy effect.  But add sugar to microwaved water, and the effect can be much more dramatic.

When you heat a cup of water or tea in the microwave, its temperature can rise several degrees above the boiling point — while the liquid remains still and bubble-free.  Why?  When water isn’t heated from the bottom up, there are fewer hot spots.  Meanwhile, in a smooth glass or ceramic cup, there are few nucleation spots.  The result:  Water can “superheat,” without boiling.

Remove your superheated cup of tea and add sugar — or drop a teabag into superheated water — and the results can be explosive.  Runaway nucleation can cause the tea or water to suddenly boil furiously.  Scalding liquid may pour over the sides of the cup, or even spray into the air.  The lesson:  You can’t tell how hot the water is just by looking.  When in doubt, let microwaved liquids sit a while before moving.