Chocolate Bloom
Tags: Knowledge, Food, Science, Cooking, Chocolate

Chocolate Bloom

One of my least favorite responsibilities is gassing up my car. I hate making the extra stop. I’d rather push the limits while driving on empty.

So, like any reasonable adult, I’ve struck a deal with myself. Any time I stop to gas up my car, I can pick out a special treat. I know, very mature of me, right?

Anyway, the reason I bring this up is that recently I forgot my chocolate bar on the passenger seat of my car.

When I was finally ready to indulge, I opened the candy only to see it covered in a white haze. It looked like mold had started chomping on my sweet treat, but luckily I knew this grayish-white coating isn’t microorganisms at all.

It’s chocolate bloom.

What’s chocolate bloom?

As an undergraduate, I first learned about chocolate bloom in a class called Confectionery Science and Technology.

I’m not joking!

This is a real class I took for college credit.

Each week we made candies ranging from bubble gum to marshmallows to toffee. Each student would leave the lab session weighed down with a backpack full of goodies.

It was here that I began to appreciate just how complex chocolate was and how easily it can develop defects like chocolate bloom.

I’m guessing many of you have seen these defects without even realizing it.

For example, have you ever seen the characteristic shiny surface of chocolate become gray or white?

That’s chocolate bloom.

It can be seen as discrete spots or more of a hazy network that traverses the surface of the chocolate. Visually, these patterns or spots may seem different, but they’re all considered bloom.

The bloomed areas might make you think the chocolate is rotten, but it actually has nothing to do with spoilage. And while it can slightly alter the texture of the bar, the confection is still totally safe to eat.

So, if it’s not microorganisms to blame, what causes this transformation in chocolate?

It turns out the culprit is cocoa butter, the main fat in chocolate.

What causes chocolate bloom?

Chocolate bloom is such a complex topic that it’s still an active area of research. In fact, the research lab that I completed my Ph.D. in always had a student or two investigating chocolate bloom.

Chocolate bloom is complicated by the fact that fats like cocoa butter are polymorphic, meaning they can take many different crystalline forms.

Most fats have three different polymorphs. We call this alpha, beta, and beta prime.

Cocoa butter, on the other hand, has six polymorphs, usually referred to as forms 1–6, which makes working with chocolate a complete headache.

Each polymorph has a different melting point and stability. This means if chocolate is melted, the cocoa butter can swap which polymorph it’s in.

When chocolate is made, manufacturers ensure the cocoa butter is in form five. This gives the chocolate a shiny look and a good snap.

But, even when cocoa butter starts in form 5 polymorph, if the temperature increases and melts the fat, it can transform into a different polymorph. Usually, one that’s more stable.

So, when I left my chocolate bar in the car, it must’ve gotten so hot that the cocoa butter began to melt. This allowed the melted form 5 crystals — the polymorph that is formed during manufacturing — to be transformed into the more stable form 6 crystals as my car cooled back down.

Here’s the problem. The form 6 polymorph is known for its large, needle-like crystals, which are separated by large crevices on the chocolate's surface. These crystals scatter light differently than form 5 and make the chocolate appear hazy and white.

In the end, it was simply a conversion of cocoa butter from form 5 to form 6 that resulted in these intricate white and gray patterns. When this happens, chocolate loses its glistening brown surface and characteristic snap when eaten.