A while ago I was cooking rice, and I noticed a recurring pattern of creation and destruction of bubbles.

It seemed like the bubble-layer would increase in height, until it 'popped', and the layer height severely decreased, see the images below, which are snips taken shortly after each other. and the Youtube video. My hypothesis is that the layer would rise to the lid, and would then squish the bubbles until destruction. But I don't have any knowledge on starchy bubble dynamics to back this up.

I don't think this is a duplicate of this question, as it is indicated that this could be linked to the starch in the water, where the other question only deals with water (without any other ingredients).

enter image description here

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    $\begingroup$ Possible duplicate of What is the reason for this pattern of noise in electric kettles? $\endgroup$ Apr 17 '18 at 15:54
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    $\begingroup$ This seems to have more to do with the mechanics of a foam of starchy water than actual boiling. In other words, boiling provides only the creation mechanism, not the more interesting destruction mechanism. $\endgroup$ Apr 17 '18 at 16:03
  • $\begingroup$ @nielsnielsen, if Chemomechanics is correct, and it's due to the starchy water, then I think it's different from kettles boiling water.? $\endgroup$
    – ROIMaison
    Apr 17 '18 at 19:35
  • $\begingroup$ got it. Let's see what the experts say... $\endgroup$ Apr 17 '18 at 22:43

This is just a guess, but, I imagine it is possible that what we see is not "repeated creation and destruction of bubbles", but rather repeated movement of bubbles up and down.

They move up under pressure built up underneath and they move down, when the vapor breaks through, which causes the pressure suddenly drop underneath and grow on top.

We can see a significant vapor activity near the valve, which is an indication that the average vapor pressure under the lid is high, but it would be difficult for the vapor to get to the top without somehow breaking through the bubbles.


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