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I buy fresh oranges wholesale so I could enjoy fresh juice every morning, I store them in the fridge (not the freezer) so they can last for a few weeks (yes, about 60% of my fridge content at any given time is just oranges).

When I take them out to squeeze them, I have noticed a peculiar thing. More often than not, about 1 or 2 of the 20 or so oranges I pick are frozen solid, like a ball of ice.

I can't find an explanation to this that makes sense to me, as:

  • I am quite sure that my fridge never goes below zero C, as I've never found any other thing in there that's frozen or frosted or something like that.
  • The frozen oranges do not seem to share a common pattern like size, color, taste. They are all quite similar, I've seen two small ones right next to each other where one is frozen and the other isn't, same thing with larger ones.
  • It doesn't seem to happen around a particular region of my fridge. I could find some near the top, but then another one at the bottom the same day, etc...
  • The proportion I described earlier (about 1 in 18-20) seems to kind of hold but I haven't measured that rigorously.
  • Could be sugar content, but I've read that a high amount of sugar actually makes the freezing point go down (!).

So, what could be going on?

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    $\begingroup$ Could it be that the oranges are touching the walls of the fridge? Especially the wall in the back where the drain for the condense is? You have probably noticed that foods or objects that is in contact with this wall freeze rather easily. $\endgroup$
    – ludz
    Commented Oct 7, 2021 at 6:36
  • $\begingroup$ @ludz you might have something there, the freezing point of orange juice is about -1.7C $\endgroup$
    – anna v
    Commented Oct 7, 2021 at 7:10
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    $\begingroup$ Trying out Ludz suggestion you could try noting the location in the fridge that this happens, you only say about top and bottom, what about contact with back wall? $\endgroup$
    – anna v
    Commented Oct 7, 2021 at 7:12
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    $\begingroup$ I’m voting to close this question because it is more suited IMO to Seasoned Advice where they do answer technical questions on food related matters. $\endgroup$ Commented Oct 7, 2021 at 7:56
  • $\begingroup$ @StephenG I think it's worth handling here so long as we treat it as a combination of thermal flow in the refrigerator and the effect of contaminants (sugar) on the freezing point of water. $\endgroup$ Commented Oct 7, 2021 at 13:49

1 Answer 1

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This is a nontrivial question... So we start by testing the most straightforward hypothesis: An orange that was deficient in sugar would freeze at a slightly higher temperature than a sugar-rich orange. It might be sugar-deficient if picked too early. This suggests that 1 out of 20 oranges off a given tree is unripe, or at least less ripe than the others.

Next time you freeze a batch, squeeze the juice from an unfrozen orange and from a frozen orange and measure their respective sugar contents. And put a thermocouple in there and measure the true temperature of the fridge as a function of time while the experiment is running.

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  • $\begingroup$ Is there an easy, homemade way to measure sugar content? Even if it's approximate, I don't have specialized equipment here. $\endgroup$ Commented Oct 7, 2021 at 6:19
  • $\begingroup$ yes, winemakers use a simple optical device called a refractometer to measure sugar content of their grape juice, in units of degrees brix. winemaking supply stores sell them. $\endgroup$ Commented Oct 7, 2021 at 6:22
  • $\begingroup$ Nice, I'm willing to make that investment and come back with my findings in a few days, all in the name of science. The thermocouple sounds like a more expensive thing, so I guess that'll have to wait. Where I'm at it's about 20ºC all the time, so it's not like they freeze due to low temp. at night or w/e. $\endgroup$ Commented Oct 7, 2021 at 6:25
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    $\begingroup$ Refractometers are very expensive. Measure the density is much easier, you can search for "degrees Oechsle", "Brix scale", or "must weight" for more information. My bet is on frozen oranges being stored close to the rear wall of your fridge, where my fridge freezes vegetables easily. $\endgroup$
    – rfl
    Commented Oct 7, 2021 at 10:02
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    $\begingroup$ This video suggests that sugar solutions twist polarized light (dextrose, right?), so maybe you could use a pair of polarized filters (quite cheap) and measure the angle of polarization of a given amount of liquid. $\endgroup$
    – rodrigo
    Commented Oct 7, 2021 at 16:45

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