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My friend (who lives in a warm, humid climate) often has issues with chocolate, due to the formation of a light-colored coating on it. I believe it is just chocolate bloom, but she thinks it's mold and should trash the chocolate. Visual inspection alone does not seem sufficiently precise to identify which of these has happened.

Is there a reliable way to test which one is the case? i.e., re-heating it, or trying to remove the coating with a knife, or some other technique which does not require using a microscope?

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up vote 4 down vote accepted

It is is almost impossible for chocolate to mold as it doesn't have any moisture, required for mold growth.

There are two types of bloom:

Sugar bloom -- wipe the chocolate with a wet finger, it will dissolve.

Fat bloom -- wipe the chococolate with a dry finger, it will feel waxy or greasy

Either tends to look like a chalky coating, not very thick, definitely not fuzzy (like mold).

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Indeed, that is a simple and convincing technique. So if after wiping the finger I still have some powdery substance which does not dissolve in water, then it's certainly mold. Right? Or could it happen that the mold might eventually dissolve? I'm expecting it should feel a bit like a Camembert cheese... – anol Aug 28 '13 at 16:44
The chances that is mold are astonishingly small, as chocolate is very inhospitable to molds, unless the chocolate was stored in very improper conditions. I don't know what mold would feel like, since I have never had it happen. I suspect it will be fuzzy as most mold fruiting bodies have that appearance. It may also be splotchy in appearance. Googling for "moldy chocolate" images didn't provide much credible information. – SAJ14SAJ Aug 28 '13 at 16:50
I believe that when it happened to my friend, it was because it had been stored in a plastic container in the fridge (which was maybe not entirely clean). This, or maybe forgetting the container on the bottom of the fridge for several months... – anol Aug 28 '13 at 17:19
That is a likely scenario for sugar bloom... – SAJ14SAJ Aug 28 '13 at 17:22
Chocolate that has been badly tempered is more susceptible to bloom, as is chocolate that has melted in it's wrapper. – silves89 Aug 30 '13 at 14:31

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