What's the Science Behind Chocolate Bloom?
- Anjali Carl
- 3 days ago
- 3 min read
One of life’s greatest joys is opening a bar of chocolate and seeing the shiny dark brown confection. However, it is equally disappointing to open that bar and see that bar dusted with a white powdery film. It tastes and smells like chocolate; it just doesn’t look like it. That white layer is called the bloom and it an an example of the chemistry behind chocolate and why it’s so temperamental.
In chocolate, there are actually two types of bloom: sugar bloom and fat bloom. While they look the same, the chemistry behind them is different.
Sugar Bloom happens because sugar is hygroscopic which means it attracts moisture. When chocolate is exposed to humidity, for example, water dissolves some of the sugar on the chocolate’s surface. When the moisture evaporates, the sugar recrystallizes leaving behind rough and grainy crystals that look white and feel sandy to touch.
Fat Bloom is the most common type of bloom and happens when the cocoa butter in chocolate melts and resolidifies but does so unevenly. Cocoa butter is a polymorphic fat which means the molecules can crystalize in six different ways. Form V is the only one that creates the smoothness and perfect snap we associate with tempered chocolate. When chocolate is tempered, chocolate makers control the temperature to encourage Form V crystals to form; this ensures the fat molecules are organizing into the right structure.
While Form V crystals are stable, they aren’t the most stable.If chocolate gets too warm, the fat crystals start to melt. And those Form V crystals can transform into Form VI crystals. Form VI are more stable but they have a higher melting point and a larger crystal structure. As the larger crystals of Form VI form, they rise to the surface of the chocolate and create that white coating. Fat bloom can happen with temperature fluctuations, improper tempering, mixing different types of chocolate with different fat compositions, and age. This is why chocolate shouldn’t be refrigerated; the temperature swings that occur when it’s taken in and out of the fridge is what causes the bloom.
Both types of bloom are due to crystallization issues but due to different mechanisms. Touch will tell you if the bloom is due to fat or sugar. Fat bloom will have a smooth and waxy surface that feels oily and melts to touch. Sugar bloom will have a more rough and grainy texture that may dissolve if you touch it with a damp finger. Chocolate itself is an emulsion- a miz of cocoa solids, sugar, and fat. When that structure destabilizes, the result is the white bloom. This is why chocolate making is so technically demanding and requires such precise focus. It requires narrow temperature windows and stable environments with respect to heat and humidity.
To prevent bloom, store chocolate at 60-70 degrees F and don’t refrigerate chocolate unless absolutely necessary. If it needs to be refrigerated, let it come to room temperature slowly and while still wrapped. Store chocolate in airtight containers to prevent sugar blook or even use silica gel packs if high humidity is common.
The next time you see bloom on your chocolate, don’t throw it away. Take a look and feel to see if you can identify the cause.
Anjali Carl is a junior at Cedar Park High School in Cedar Park, Texas. They have been excited about food science since making ice cream in a third-grade science class, and now enjoys baking and recipe development. Through their Girl Scout Gold Award project, they created two cookbooks focused on reducing food waste for food pantries and college students. They plan to study food science and eventually become an ice cream chemist.
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