[paul.fr]

Why does adding milk to my favourite  cereal, rice krispies, make them go snap, crackle and pop?

[Karen W.]

I used to eat those, and always wondered why too. They do get soggy fast if you don't partake soon after the milk is applied... I love wheat chex and shredded wheat and Those lovely cinnamon wheat chex YAYYYYYYYYYYY!

MAybe they pop because thei are little puffs with lots of air space to fill up inside them.. LOL

[Karen W.]

Maybe the spaces are forcing air out of the little crispies and this in turn may force air pockets to the surface causing bubbly poping noises that can be heard as it invades your serial!

[neilep]

Those lovely cinnamon wheat

YUK !!...the Devils Scrotum fungus raises it's ugly head again !!

[Karen W.]

LOL!! You are so full of it it 's oozing from your ears...LOL HUGS

[another_someone]

Doubt that it is the air itself, but I suspect the cellular structure of the walls expanding as the absorb the moisture, but the irregular expansion possibly is causing the whole structure to shatter (just speculation).

[Karen W.]

Hummm thats interesting. they become soggy little bits very quickly!

[Soul Surfer]

They make puffed cereals by heating the cereal well above the boiling point of water in a pressure vessel and then letting it explode by releasing the pressure suddenly.  Puffed wheat used to claim to be "shot from guns".  The water in the cereal boils violently explodes, cooks the cereal and makes it crispy.  Presumably there are small bubbles still inside the body of the cereal containing either residual pressure or vacuum and when the milk makes the cereal soft they explode or implode.  My guess is that they are more likely to be little bubbles with vacuum inside because the water that expanded as it turned to steam has now condensed.

[daveshorts]

I think you are right about how they are made, but I think the mechanism for the crackling in rice cripies is to do with stresses in the shell, because if you look at them they have holes in them, so I don't think it can be due to contained vacuum or pressure.

[Soul Surfer]

That sounds logical.  I was a bit worried about the possibility of any sort of pressure difference being maintained for a long period rapid stress relief as the material softens in the milk sounds a better bet.

[daveshorts]

I expect you will get the half in the milk swelling rapidly and cracking the half that is still dry.