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Why is frozen milk yellow?

  1. Aug 30, 2011 #1

    cmb

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    When you freeze semi-skimmed milk, it goes yellow, and when you unfreeze it, it goes back to white.

    I would tend to have assumed that the two colours were the same (i.e. the 'white' is just a very very light shade of the same yellow colour) so maybe the question is why the shade of it changes.

    Why do we get this change of appearance?
     
  2. jcsd
  3. Aug 30, 2011 #2

    xts

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    My ad hoc explanation (they often occur to be wrong!)

    As you freeze milk, relatively large the crystals of pure ice are forming, taking out water - thus making the liquid part to be a kind of condensed milk or coffee cream. Those are yellowish too. Light comes through large, transparent crystals of ice, getting scattered only on yellowish condensed milk.
     
  4. Aug 30, 2011 #3
    Frozen adolescent yak urine turns royal purple when it freezes, so go figure. :smile:

    Actually I think it's due to separation of fatty components due to different freezing temperatures. To test this you could try freezing different kinds of milk - whole, lowfat, nonfat, etc. I would guess that nonfat milk doesn't turn yellow, but I haven't done the experiment myself.
     
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