When chocolate's exposed to too much moisture, sugar bloom can happen. That's because sugar is a hygroscopic substance -- in other words, its crystals suck up moisture and retain it. If sugar gets wet enough, it might even dissolve a bit in the surface water. When the chocolate dries, the larger sugar crystals are left behind on the surface as a white powder.
Sometimes, the problem happens long before the product hits the shelves. If the chocolate wasn't properly refined (which reduces the size of its sugar crystals) during the chocolate-making process, the larger crystals could absorb moisture more readily. If your chocolate has a delicious filling of some kind, the culprit could be too much liquid introduced when it was formed. Sugar bloom is typically a storage issue, though; if you keep chocolate in a damp room, condensation can form on its surface. This can also happen at the grocery store or in your own fridge, so stash your chocolate in a cool, dry place if you want to avoid sugar bloom.
OK, so we know when sugar's the cause of bloom, but what about fat? Improper storage can also cause fat bloom. If it's just warm enough, the cocoa butter in the chocolate will separate a bit and settle on the surface of the chocolate, forming greasy streaks. Fluctuating temperatures can also be to blame.
However, mistakes during the chocolate-making process are most likely to cause fat bloom. Chocolate must be tempered -- a process of repeatedly raising and lowering the chocolate's temperature to create uniform, stable crystals of cocoa butter. If tempering isn't done just right, the differently sized crystals can transform over time, and voila -- you've got bloom.
Here are some other potential fat bloom-causing scenarios:
- The chocolate maker doesn't allow the sweet treat to cool properly before packaging it.
- There's another type of fat injected into the chocolate that melts at a different temperature than the cocoa butter does (this is sometimes done in less expensive chocolate because cocoa butter is pricey).
- Warm chocolate is paired with a cold filling (in general, chocolates with a filling that contains fat are more likely to fall prey to fat bloom).
Blame the chocolate maker, blame the store or blame yourself. But if you don't want to eat bloomed chocolate, you can probably find somebody who will!
- Beckett, S.T. "The Science of Chocolate." Royal Society of Chemistry. 2000.
- Longchampt, Pierre and Richard W. Hartel. "Fat bloom in chocolate and compound coatings." European Journal of Lipid Science and Technology. April 2004. (Jan. 14, 2012) http://onlinelibrary.wiley.com/doi/10.1002/ejlt.200400938/pdf
- Nemours. "Candy Experiments: Chocolate Bloom." KidsHealth. 2012. (Jan. 11, 2012) http://kidshealth.org/kid/closet/experiments/candy_chocolate.html
- Partos, Lindsey. "Fat bloom findings bring savings for chocolate makers." Food Navigator. Sept. 22, 2004. (Jan. 15, 2012) http://www.foodnavigator.com/Science-Nutrition/Fat-bloom-findings-bring-savings-for-chocolate-makers
- Smith, Kevin W. et al. "Effect of Antibloom Fat Migration from a Nut Oil Filling on the Polymorphic Transformation of Cocoa Butter." Journal of Agricultural and Food Chemistry. Feb. 7, 2008. (Jan. 15, 2012) http://dx.doi.org/10.1021/jf072151s
- Struempler, Barbara. "Blooming Chocolate Won't Hurt You." Alabama A&M and Auburn University Cooperative Extension System. 2012. (Jan. 11, 2012) http://www.aces.edu/dept/extcomm/newspaper/chocolate2.html