The Truth Behind the Dreaded Chocolate 'Bloom'

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old expired piece of chocolate in wrapper with white stuff called a bloom

Jennifer A Smith / Getty Images

Have you ever wondered what that white stuff is that forms on the surface of chocolate that has been sitting around? More importantly, have you ever wondered if you should still go ahead and eat it?

That white stuff that you might call icky white stuff is technically called a "chocolate bloom." But why does it happen and should you steer clear of chocolate that has "bloomed?"

Those are the questions recently tackled by a research team from the German national research center Deutsches Elektronen-Synchrotron (DESY), the Hamburg University of Technology (TUHH), and Nestlé (which funded the research.) The team sought to explain the bloom so they could learn how to prevent it, and so they could answer the question once and for all about whether or not bloomed chocolate is safe to eat.

Using a powerful X-ray machine called the PETRA III, the researchers were able to study the process of chocolate blooming in real time. The team ground up the chocolate into a fine powder to speed up the blooming process and then added sunflower oil to each sample to speed up the migration of fats in the mixture. Using the PETRA III, researchers were able to watch each pore and crystal of the chocolate to determine what was happening during the blooming process.

What they found was that the chocolate bloom is caused by a migration of liquid fats to the surface of chocolate where it crystallizes.

“This can happen when liquid chocolate cools down in an uncontrolled manner and unstable crystals form. But even at room temperature, a quarter of the lipids [fat molecules] contained in chocolate are already in a liquid state,” said Svenja Reinke, the lead researcher of the study.

So what does this mean for you? Two things. First of all, that chocolate bloom is just crystallized fat, so it's perfectly safe to eat. And second, it means researchers — and chocolate manufacturers — are well on their way to better understanding, and thus preventing, the dreaded chocolate bloom from happening in the first place.

And that is some seriously sweet news.

The study was published in the recent issue of the journal Applied Materials and Interfaces.