Hard Candy Mysteriously Melts Over Day or Two After Bring Placed In Orange Peel
April 12, 2012 12:03 PM   Subscribe

BotanyFilter: Why does hard candy melt when placed in an orange peel?

When sucking on a piece of hard candy recently, I needed to take a pill and spit out the candy into a piece of orange peel I had lying nearby on my desk. I promptly forgot about the candy and it remained lying in the bowled surface of the orange peel for a day or two until I rediscovered it -- but it had melted in the peel, despite the room being of ordinary temperature (~73F).

I decided to test it out with a piece of un-slobbered candy of the same kind (this in orange flavor, ingredients: sugar, corn syrup, citric acid, artif.flav, FD&C yellow 5 red 40.) and a day or so later it also had melted inside the bowl-shape of the peel.

I'm not sure what good or evil could come from knowing this, but any idea why? The candy had set in the same room for 4+ weeks without melting, but melted (or liquefied, broke down, etc) inside the orange peel in a matter of a day or two. It could serve as a technique for melting candy without using any heat source, although it takes a long time..
posted by Quarter Pincher to Food & Drink (9 answers total) 1 user marked this as a favorite
Sufficient local humidity? It doesn't take much for an unconstrained piece of candy to begin liquifying.
posted by aramaic at 12:04 PM on April 12, 2012

Yup, humidity.
posted by phunniemee at 12:09 PM on April 12, 2012

Best answer: Hygroscopy is the word you are looking for. It's not melting, like ice, it's dissolving in water which it has sucked out of the air and the peel. Sugar (and corn syrup) is the culprit.
posted by bonehead at 12:11 PM on April 12, 2012 [4 favorites]

The next test I'd do would be to set an unwrapped candy on the desk right next the orange peel as well as one on the orange peel. If you come back to a puddle on the desk along with a puddle in the peel, then it's got nothing to do with the peel. and it's all humidity.

If the one on the desk is still intact, then the peel is contributing something.

I don't know what that something would be. Maybe just water. Maybe the citric acid in the peel has something to do with it.

I personally don't think humidity is the whole story. I've left unwrapped hard candies out in all types of weather, and while I've come back to candies in various states of stickyness, I don't think I've ever come back to a puddle.
posted by chazlarson at 12:51 PM on April 12, 2012 [3 favorites]

Some time ago I discovered that candy corn used as decoration on a cupcake (like, stuck into the icing) would dissolve if left there for a day or two. Hygroscopy seems to explain both of these phenomena.
posted by makeitso at 1:04 PM on April 12, 2012

I'd bet that water is largely coming from the orange peel. Peels can be 80% water.

Hard candy can go sticky on a humid day. To completely liquefy, though, I suspect, the candy would have to be able to draw moisture out of the peel.
posted by bonehead at 1:05 PM on April 12, 2012

Orange peels also contain significant amounts of d-Limonene, which is a strong solvent (used in 'bio' degreasers and dewaxers).
posted by bumpkin at 1:23 PM on April 12, 2012 [1 favorite]

Citrus oil will essentially melt sugar, and hard candy is mostly sugar.
posted by dizziest at 2:44 PM on April 12, 2012 [1 favorite]

Best answer: I wanted to figure this out, so I assembled a few supplies and looked at what happens when you put a candy in an orange peel as well as a few other things.

I wanted to try to address the three main hypotheses offered above:
1. The candy absorbed water from the humidity in the air
2. The candy absorbed water from the surrounding peel
3. The dissolution of the candy was sped-up by the d-limonene in the orange peel.

I looked at candies alone, candies in orange peels, and candies in cups carved from potato. I had a set that was covered, and a set that was open to the air.

After 14 hours, the candies alone hadn't changed at all. No more sticky, no mass gain. The candies in the peel were floating in a thick liquid, coloured pink by the candies. The candies in the potato cups had completely dissolved (covered) and mostly dissolved (uncovered).

After a few calculations (see the link below for more details), it was clear that humidity wasn't a major factor. The weight of the bare candy had not changed (to +/- 0.02g), and the uncovered peel and potato cup had both lost mass to evaporation. If anything, the systems were losing water to the air, not gaining. Humidity, guess number 1 doesn't appear to be a major source of the liquid.

There were fluids around the candies, however, in both the peels and the potatoes, exactly as Quarter Pincher reported. I didn't see complete dissolution in the peels, as Quarter Pincher did, but then I only looked a the peels after half a day. In my opinion, the source of the liquid is pretty clearly moisture drawn from the peels. The effect being seen for both the covered and uncovered peels seems to rule out atmospheric moisture as a factor. Hypothesis two seems to work.

I included the potato cups to try to get at the third idea. It's credible: d-limonene is used in a number of cleaning products. If anything though, the potato cups resulted in more complete and more rapid dissolution of the candies. From this, it didn't appear that the citrus oils were that important.

I wasn't convinced though. Were potatoes good surrogates for the peels? The moisture contents of the potato were a bit higher: about 75% compared with about 60% for the peels. I was concerned that the dryness of the pith compared to the wet surface of the cut potato would have an influence too.

I decided to look at the effects of d-limonene more directly. I put three candies into shot glasses and covered them with tap water, an 8:1 water:d-limonene mixture and a shot of pure d-limonene. Overnight, water and mixture shots turned colour, and the candies dissolved at about the same rate. The one in the d-limonene alone had no change at all by the next morning.

Based on both observations, I'm not convinced that the oils from the citrus peel made a big difference.

So, in my opinion, what matters is the moisture in the peel. It's the source of the liquid that dissolves the candy. Moisture from the air and oils from the peel don't seem to be very important.

Here is a more detailed write-up with charts and tables and graphs (and a shameful confession).
posted by bonehead at 11:41 AM on April 14, 2012 [7 favorites]

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