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On Chocolate Bloom

Following last week’s discussion on how to “bloom” cocoa powder, several readers wrote in with questions about chocolate bloom. They wanted to know what it is exactly and how it works.

Simply put, “blooming” is a term used to describe what happens when some of the substances that make up chocolate leech out of it, pool up on the chocolate’s surface, and crystallize into tan or grey-ish films. This generally has the effect of ruining the chocolate’s texture, and really its flavor too, since the smoothness, snap, and meltability of chocolate have a great deal to do with how we experience it.

Just so we’re all clear in our terms, bar-type chocolate is a suspension. Which is to say it is a type of colloid (“stuff dispersed within other stuff“), comprised of cocoa solids, small sugar crystals, and milk solid particles, all suspended within a medium of cocoa butter crystals. It’s a type of suspension that quite easily breaks down, however, in the face of changes in temperature and humidity.

As we all know, it doesn’t take too much heat to melt chocolate. And the finer the chocolate, the more readily it melts. This meltability is a factor of two things. First, a relatively high proportion of cocoa butter, and second, a very uniform crystal structure. Well-tempered chocolate contains just three types of fat crystals (as compared to, say, butter, which can have dozens). The very simple and orderly crystal structure is what gives a high-quality chocolate bar its “snap”. It’s also what gives good chocolate its melt-in-the-mouth texture, as those three kinds of crystals all have melt points that are within a few degrees of each other. Raise them to the temperature of, say, the inside of a human mouth, a boom — they all go liquid more or less as once, bathing our taste buds in viscous, chocolatey goodness. This tendency to melt quickly and all-at-once is what’s known in scientific circles as a “sharp” melting point.

That sharp melt point can work against you, though, if the chocolate gets up to temperature before it arrives in your mouth. Chocolate, particularly very fine chocolate, starts to soften considerably as it approaches 85 degrees, and puddles at around 90. Most of us don’t try to eat it in that state, slurping it off bits of wrapper and foil (though I could tell you a few stories about Mrs. Pastry that would shock even the most round-the-bend chocoholics out there). Most of us would rather try to re-solidify the melty stuff by putting it into the refrigerator or freezer.

Which is an imperfect solution to put it mildly. For when left to its own devices, cocoa butter doesn’t form nice, neat, orderly, LEGO-like crystal structures. It rather forms random, disordered, jumbly ones, comprised not of three different crystal types, but six, four of which are highly unstable. This crystal mishmash takes up more space then the ordered rows it replaced, the result being that some of the cocoa butter is squeezed out onto the surface of chocolate mass, where it pools up and finally re-crystallizes into a grey-brown film.

In the end the re-firmed chocolate is a shadow of its former self: a good deal softer, waxier and/or chalkier than it was when it left the factory, with a dull finish (again the result of randomized crystals, which don’t reflect light rays as efficiently as tidy crystal rows do). It’s all a rather sad story. Though there is a silver lining: if you’re up for re-melting and re-tempering your bloomed chocolate, you can return it to its earlier, lovelier, tastier state.

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