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I've had a few Hershey chocolate bars in the past that had a white surface coating. After a bit of searching, I found this is called bloom. I'm not sure if this is sugar bloom or fat bloom, but it was from a newly bought chocolate bar. I actually, and apparently unpopularly, enjoy this effect. Is there a way to induce it in store bought chocolate?

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Sugar bloom is a bit more stable than fat bloom, so if you like that effect I'd suggest that you try to leave the chocolate first in a slightly warm and damp environment, the sort of temperature that would make it really soft, and once it is "sweating" move it to a freezer.

Sugar bloom is caused when the moisture from the chocolate gets slight separated from the chocolate, it dissolves the surface sugars and then evaporates, leaving sugar crystals behind. So it might be possible that spraying a soft warm mist of water might help accelerate it.

I never tried to have sugar bloom intentionally, but I'll give this mist technique a shot and let you know.

  • The mist technique worked like a charm. :) – TBonamigo Nov 16 '17 at 11:14
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Since @TBonamigo have already addressed sugar blooming, I will comment on fat blooming.

Fat blooming is the migration of fat from the bulk of the chocolate to the surface. Why and how blooming happens is not an easy question, and there is a lot of research in the industry trying to address the problem.

But we can build a heuristic picture. The first important information is that when liquid cocoa butter cools, it forms a solid crystalline structure. Different spatial arrangements of the fat molecules lead to different crystalline structures, each characterized by different physical properties such as melting point, specific heat, and resistance to strain.

If you melt your chocolate and let it cool randomly, it will (almost) randomly crystallise in these different shapes. The result is a polycrystalline solid. Since some of these crystals have a lower melting point, imagine that with temperature fluctuation some of them can melt and become a liquid trapped in the unmelted crystal. But since liquids occupy a higher volume, this generates pressure that 'push' the liquid fat to the surface. This migration also increase the porosity of the chocolate which itself helps blooming.

Chocolate makers usually want to reduce this effect by controlled cooling o form a uniform structure with the most stable crystals. If most of the crystals have the same (high) melting point you reduce blooming. This is achieved by tempering, and your industrial bar is usually in this phase.


With the science in mind, an easy way to get fat blooming is untempering your chocolate by melting it completely and let it cool into a polycrystal at room temperature. From personal experience this usually leads to blooming within a few days. If you cool in the fridge and after let it sit at room temperature It might even accelerate the process, since you are creating more drastic temperature fluctuations.

  • Even just cycling from warm room temp to cool a few times can do this IME -- but that's uncontrolled. If you've got cold nights and sunny days, try leaving it in a car! – Chris H Nov 16 '17 at 21:45
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If you put it in the freezer for a while, it sometimes happens. Or long time sitting on the shelf (room temperature) I mean a long time, like years (not decades).

  • My freezer sits around -15c/5f. About how long should I leave the chocolate in for? And should I remove it from the packaging? – Daffy Nov 16 '17 at 1:52
  • Wow, I don't know how long to leave it in for. I just noticed that effect sometimes on forgotten chocolate, so don't remember when it was put into the freezer. But no, you don't have to remove the wrapper. The chocolate doesn't seem to taste particularly different to me though, when it has that white "bloom" on it. – Lorel C. Nov 16 '17 at 2:00

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