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I put bananas, honey, almonds and skimmed milk in the blender and blended it. When it was all blended the surface had a layer of tiny bubbles and there was a audible fizzing sound, like from a soft drink, both of which remained for several minutes.

Normally I'd assume the milk had turned. However this has happened enough times to rule that out. And it never happens with whole milk.

Does anyone know why this happens?

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During blending, air is put into the milk mixture. Once you switch it off, not all air is kept inside the milk but makes it's way to the surface. These are the bubbles that make you think your milk is fizzy.

Without being a chemist I assume full fat milk has more fat, therefore the emulsion is somewhat "thicker" and thus can hold the air better. There are also bubbles with full fat milk, but less than with skimmed milk. Sort of.

  • So why only with skimmed milk? The fat in the whole milk keeps the bubbles intact longer? Or what is your actual explanation for this phenomenon in skimmed milk, as Daron asked? – Lorel C. Sep 6 '17 at 15:11
  • @LorelC. Answer updated – eckes Sep 6 '17 at 15:14
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    @lorelc The foam stability of milk/cream is known to be fat dependent, with several "optimal" zones also depending on the temperature you use. I suspect it gets even more complicated for this kind of mixture. If you want to dive into very deep details, look around for capuccino nerds trying to get microfoam instead of "construction foam", there are endless threads about it on the Internet. – rumtscho Sep 6 '17 at 15:52

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