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My mom gave puffed rice to eat, I had quite wet hands. I saw that, each puffed rice pieces started hanging to the hand, when I brought my hand in contact with them. I thought about electrostatics initially to be the cause. Actually, the electrostatics usually deals with rough surfaces. Here due to hand being wet, it has got smooth surface. Then, what might be reason? I started thinking, suddenly I thought it to be because of hydrophillic nature of kadale puri (puffed rice). Is it really because of hydrophillic nature of puffed rice?

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    $\begingroup$ you should better use the term 'Puffed Rice' rather than 'kadale puri'.. $\endgroup$ – blackSmith Nov 6 '13 at 13:21
  • $\begingroup$ I think it's a combination of hydrophilic surfaces trying to spread water out and water's high surface tension trying to pull itself back together, creating a sort of elastic tension. Likely more of a physical process than a chemical one. $\endgroup$ – Nicolau Saker Neto Nov 6 '13 at 13:50
  • $\begingroup$ In many cases of stickiness, where obviousness is not a given (thus mostly excludes dipole-dipole int.), it is a slew of usually weak intermolecular forces such as the London dispersion force which are increased by special material properties such as surface area and resonance assistance. $\endgroup$ – Lorenz Lo Sauer Nov 7 '13 at 18:56

This thesis, (Texture and Hydration of Expanded Rice, Clive Norton, September 1998), has a vast amount of information on rice, including puffed rice.

Rice is mostly starch, which when heated is gelatinised. This causes "the breaking of hydrogen bonds between poly-α-1,4-glucan chains, leading to loss of crystallinity" allowing those hydrogen bonding sites to absorb more water. The loss of crstallinity also leads to air pockets making puffed rice sponge like. The starches become "interspersed with gas pockets" which are filled by water through capillary action.

So, puffing makes the starch more hydrophillic, exposing hydrogen bonding sites, and the air pockets act as capillaries. The puffing also increases the ratio of surface area to weight. These factors cause the rice to be liftable with a "water chain".


Hydrophilic surface and capillary action is sertainly part of the answer together with the surface tension of water trying to minimize its surface area. But another part is probably the very low weight of puffed rice! That makes the effect of the beforementioned forces more noticeable. If the rice grains would be heavier (denser) you would probably not notice the same stickyness.


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