Why Do Rice Crispies Pop?

When the cereal is exposed to milk or juices, the walls tend to collapse suddenly, creating the famous "Snap, crackle and pop" sounds.

http://en.wikipedia.org/wiki/Rice_Krispies

GA to you Techart!

Great reply. Informative, yet concise!

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Rebuke for erector1:

There is such a thing as the internet, and a search engine called Google. You could have found what you were looking for VERY EASILY by typing <rice krispies> in the Google search box. You would have had an immediate answer without having to wait for a reply to your post.

Learning to do/learn things for yourself strengthens your character. Sharing what you have learned makes you wise.

Mike

Yeah, but he can't really read... his writing is a proof.

Copied verbatim from Wikipedia, and nothing about mechanism.

If I'd Googled that answer I would not have been satisfied.

Let's have something that actually explains it.

Whoa! My bad - I usually check. This time I didn't.

Mike

Good Answer. In my weird imagination, it would be like pump cavitation in slow motion. The noise in pump cavitation is vapor bubbles suddenly colapsing under increased pressure. With Rice Krispies, the puffed rice "bubble walls" slowly collapse at a random frequency for the distinct noise. For some reason, I'm not surprised Wiki has a similar reason.

How else would you convince children to eat the stuff?

It is made under temperature leaving some stress in the dry wand.

In other words, the crispy side of the structure snaps, crackles, or pops when the soggy side collapses. The crispy side fails under tension.

The soggy side collapses because water in the milk forms hydrogen bonds with the hydroxyl groups on the starch, disrupting the hydrogen bonds that were formerly between starch molecules. When dry, hydrogen bonds between starch molecules are fairly strong.

So, is this reacton releasing hydrogen?

Could this be the Holy Grail of untapped energy production? A kids breakfast food?

Im going out right now tonight and dumping a box of Rice Crispies and a gallon of milk in the tank of my hydrogen powered car.

I'll let you all know what happens. bye

P.S. I got dibbs on the patent.
And let your kids know that they can't smoke within 150 feet of the breakfast table. SAFETY FIRST

I agree that the original answer was what rather than why. But I don't quite understand this answer - perhaps something is missing?

I understand that the water softens the side it contacts, but I don't recollect seeing evidence of the tension (bending forces?) that breaks the crispy side?

Can you elaborate, or do I need to buy some so I can make some observations?

I managed to follow this up a little. There were clues, but I didn't find any of the theories to be entirely convincing.

What seems certain:
. Rice Krispies are built from microporous starch that softens when exposed to water.
. There is a lot of built-in strain.

My provisional theory:
The softening of part of the walls of a pore redistributes the strain. At some position in the wall the strain exceeds breaking point, resulting in further redistribution that sets up a chain reaction. The surviving porous part of the Krispie is quite resonant, allowing coupling to the air to create the crackling you hear.
The process may be assisted by surface tension and/or by partial weakening of adjacent walls by the moisture.

Possible experiments to debunk the theory:
Isolate a Krispie, and break a bit of wall using some other method*: if this doesn't make a noise more than one time in about 20 the theory is probably junk.
*Anyone got a quiet enough pulsed laser they could focus onto a Krispie?
Place Krispie on droplet of water that is only just large enough to cause pop, and take pictures before and after - if the disruption does not extend beyond the damp section the theory is again unlikely to be correct.

Over to someone with appropriate equipments?

Hmmm. But is it the strain that causes the sudden collapse, or is it the stress?? We should send the problem to the Time Warp TV program producers and let them do a super high speed photo study of various liquids being added in micro-thin layers, vs. dropping the cellular gains into various liquids. How much does carbohydrate wetting, liquid absorption potential and liquid surface tension play in the eventual collapse? If one were to make a cereal grain 10,000 times larger than the actual cereal grain, would the shock wave of the wall collapse break the sound barrier? Could this be the ultimate anti-terrorist weapon of the future? And in addition, feed the mal-nourished of the world?

You're joking, ...right?

I'm with CMTec, I can't believe anyone is taking this seriously.

Shouldn't we be disussing more important issues such as ,can the Roadrunner really run that fast. Or why do Penguins have such short legs?

merlin.

"Shouldn't we be disussing more important issues such as ,can the Roadrunner really run that fast. Or why do Penguins have such short legs?"

Or how long does it take a grasshopper with a corkscrew leg to kick the seeds out of a dill pickle.

The reason is because Snap, Crackle, and Pop are jumping out of the rice krispies.

This is why you hear the noises. It's obvious and of course they are on the box.

Plus, you get a special surprise in each box of Kellog's rice krispies.

This explaination is not in wikipedia and it is top secret...don't tell anybody.

Especially the keebler elves.

What are the Keebler elves and can you eat them?

You are all wrong... They are filled with "Pop Rocks"

http://www.pop-rocks.com/

Josh.

Think, surface tension. Now go do the rest.

No GA's necessary...as they have thus far proven fairly worthless.

Don't have a theory to put forward, but think I see a problem with previous (except jumping mascots for which I have no theory).

But if this is based on assymetrical breakdown, followed by rupture/destruction of one side and sogging of the other, shouldn't I end up with mush upon contact with the milk?

This is a good one - I can't resist throwing in my two cents.

How about this...

Think 'wicking' inward equally in all directions. The air inside is trapped and the pressure is building, Building, BUilding, BUIlding, BUILding, BUILDing,... BUILDING... POP!

I'm not sure what makes a snap or a crackle. Maybe those are the ones that are immersed asymetrically? Oops, sorry. Snaps and crackles are off topic.:-)

Surface tension forces won't pop for that reason

One word: "Magic"

Here's an alternative theory I've found:

http://www.livescience.com/environment/060424_MM_rice_krispies.html

http://channels.isp.netscape.com/whatsnew/package.jsp?name=fte/ricekrispies/ricekrispies&floc=wn-nx

It says that the crackling from Rice Krispies comes from air escaping cavities by shattering the cavity walls. The experimental test is to hold a considerable number of rice krispies under water and see if air bubbles are released.

Personally I like to believe that those pops are sonic booms. You see, the tip of the whip is traveling faster than sounds so......wait, what were we talking about again?

Hi Roger

You made the two links the same - though when I followed the text the second is just a reportage of the first, so not worth it.

As no evidence is presented either way, I'm not convinced that surface tension is a major contributor. It looks as if I will have to buy some krispies and experiment with different fluids. If it's purely release of stress you'll get just as many crackles from a low-tension fluid (though possibly earlier). If surface tension is required, you will get far more pops from the standard fluid. (Personally, however, I don't fancy eating soap-loaded krispies).

Thanks for the heads up, I fixed the link. Yeah, I'm not sure what to believe either. Clearly the high temperatures that they are baked at make them glassy, and it's the shattering of that glass that's making the sound. Yet I'm not clear as to the cause of the shattering. The air pressure causing the pores to pop sounded reasonable, but so did the tension explanation.

Either way, it's a great cereal.

Roger

I thought those explanations were the same - that surface tension of fluid at small radius can create very high air pressure.

One reason I'm a doubter is that the air inside a krispie immediately after forming and cooling must be lower than atmospheric - so it cannot be more than atmospheric while still packaged. Far a good crackle due to compressed air, you require an adequate combination of pressure and mass - and I suspect this would need a hollow tube; releasing stress in a glassy solid is quite another matter.

Oh, I was reading the stress/strain explanation as not related to air pressure but rather expanding of the starch itself. As parts of the rice krispie gets absorb water (from the milk), it causes a deformation of the krispie resulting in some of those internal cavities breaking from the stress/strain.

The other explanation I read as when milk fills the cavities it causes an increase in air pressure until one of the cavity walls break.

One test could be to gently heat dry rice krispies (very gently). If it starts making the characteristic snap crackle pop sound than I would lean more towards air pressure and exploding cavities rather than structural instability.

Sorry - I had misread your intention.

To my mind the three plausible mechanisms (so far) can be abbreviated as:
a) Expansion of cellulose
b) Release of built-in strain
c) Air pressure build up due to surface tension
(With the third being lesslikely IMHO)

Whichever mechanism dominates, I don't think I would expect any joy from simple warming, on the basis that the krispies have already been cooled from a drying temperature?

You Wrote:"Whichever mechanism dominates, I don't think I would expect any joy from simple warming, on the basis that the krispies have already been cooled from a drying temperature?"

That's true. I wonder if the pores that are formed during heating have negative pressure after cooling? A semivacuum? Maybe when these Krispies come in contact with the milk, water, whatever it compromises the strength of these "bubbles" in the Krispie and they implode? Can we add that as option #4?

Hardness of the rice shell for pressure build-up of the popping of the starch, moisture content of the rice produced by steaming the rice a bit to cook the rice's starch. The moisture(H2-O) converts the starch into something (H-C-O) releasing (C-O). Vuala! pop starch/rice.

Am I reading this right? there's no chance of chemical conversions on the plate.

What's the next question? How do they get the caramel in a Caramilk bar? LOL

sooo... How many licks does it take to get to the center of a tootsie roll pop?