Food · IN60SECONDS

Why does chocolate turn white?

It’s called bloom, and it isn’t mold. Fat bloom is cocoa butter crystals showing up on the surface, and sugar bloom is sugar dissolved by moisture that dries into crystals.

Quick Answer

Chocolate turns white because of “bloom,” a change to its surface, and it isn’t mold. There are two kinds. Fat bloom happens when cocoa butter, the fat in chocolate, forms new crystals that reach the surface and scatter light, leaving a dull, whitish or streaky film. Well-made chocolate is “tempered” so its cocoa butter sets in a stable form called Form V, which gives it a glossy shine and a clean snap. Over time, and faster with warm storage or temperature swings, Form V can change into a more stable form, Form VI, whose larger crystals look white and can feel gritty. Sugar bloom is different: moisture, such as condensation, dissolves some of the sugar on the surface, and when the water evaporates the sugar re-crystallizes as a dry, dusty white layer. Poor tempering and warm or humid storage make bloom more likely.

Key Facts

Fat bloom: Cocoa butter crystals reach the surface and form a whitish film
Sugar bloom: Moisture dissolves surface sugar, which dries into white crystals
Causes: Poor tempering, temperature swings, and warm or humid storage
Is it mold?: No. Bloom is a change in fat or sugar crystals

Fat bloom vs. sugar bloom

	Fat bloom	Sugar bloom
What it is	Cocoa butter crystals on the surface	Sugar crystals left on the surface
What causes it	Poor tempering, or warm storage and temperature swings	Moisture that dissolves the surface sugar
How it looks	Hazy, streaky or dull	Dry, dusty or gritty

Sources: Chemistry World, the American Chemical Society’s journals and Popular Science.

Why tempering matters

Cocoa butter can crystallize in six different forms. Chocolate makers melt and cool the chocolate carefully, a process called tempering, so the cocoa butter sets in Form V, which gives chocolate its gloss, snap and a melting point just under body temperature. Well-tempered chocolate sets quickly with a glossy finish.

How fat bloom forms

Even well-tempered chocolate slowly changes. Form V can transform into Form VI, the most stable form, and untempered chocolate does it faster. Form VI crystals are large, scatter light and feel gritty, which is why fat bloom looks whitish and dull. Temperature swings speed up the change by letting small crystals melt and re-form on larger ones.

How sugar bloom forms

Sugar bloom has nothing to do with fat. When moisture, such as condensation from a refrigerator, lands on chocolate, it dissolves some of the sugar at the surface. When the water evaporates, the sugar recrystallizes into a grainy white layer.

Myth vs. Fact

MythWhite chocolate bars have gone moldy.

FactBloom is a surface change in fat or sugar crystals, not mold.

MythThe refrigerator keeps chocolate from blooming.

FactMoisture and condensation are a classic cause of sugar bloom, and temperature swings can cause fat bloom.

The Bottom Line

Chocolate turns white when cocoa butter crystals or sugar crystals form on its surface, a change called bloom. It isn’t mold, but temperature swings, moisture and poor tempering make it more likely.