Fat Bloom: Why Chocolate Turns White or Grey
Fat bloom is the dull grey or white film, streaks or spots that appear on the surface of chocolate when its cocoa butter has rearranged into the wrong crystal form. It makes chocolate look old and feel less silky, but it's harmless to eat.
Cocoa butter and its crystals
Cocoa butter can crystallize in six different forms, numbered I to VI. Only Form V gives chocolate its glossy surface, clean snap and smooth melt right around body temperature, about 34 °C / 93 °F. Tempering chocolate is the process of encouraging only Form V crystals to form.
When chocolate's crystal structure is disrupted, some cocoa butter melts or migrates to the surface and resets as larger, unstable crystals (or slowly converts to the more stable Form VI). These larger crystals scatter light, which is what looks grey-white.
Common causes of fat bloom
- Poor tempering. Untempered or badly tempered chocolate sets soft, streaky and bloomed within hours or days.
- Heat. Chocolate left in a warm car or sunny window partly melts, then re-sets in a disorganized way.
- Temperature swings. Repeated warming and cooling gradually pushes cocoa butter to the surface.
- Fillings. Nut pastes and pralines contain liquid oils that migrate into the chocolate shell and soften it.
- Time. Over many months, even well-tempered chocolate slowly shifts to Form VI and blooms.
Fat bloom vs sugar bloom
| Fat bloom | Sugar bloom | |
|---|---|---|
| Cause | Cocoa butter recrystallizing | Moisture dissolving surface sugar, which re-dries as crystals |
| Look | Grey streaks, swirls, soft white film | Dull, powdery white coating |
| Feel | Slightly greasy, smears | Dry, dusty, rough |
| Melts on touch? | Yes | No |
| Common trigger | Heat, poor tempering | Fridge condensation, humidity |
Sugar bloom happens because sugar is hygroscopic: when cold chocolate comes out of the fridge, moisture condenses on it, dissolves some surface sugar, then evaporates and leaves sugar crystals behind.
How to prevent bloom
- Temper properly: for dark chocolate, melt to 45–50 °C / 113–122 °F, cool to 27–28 °C / 81–82 °F, then rewarm to 31–32 °C / 88–90 °F.
- Store at 15–18 °C / 59–64 °F and below about 50% humidity.
- Keep it away from heat sources and strong odours; cocoa butter absorbs smells.
- If you refrigerate it, wrap tightly and let it warm up fully before unwrapping.
How to fix it
Melt the bloomed chocolate gently, over a bain-marie or in short microwave bursts, and re-temper. Or just use it in brownies, ganache or hot chocolate, where crystal form doesn't matter.
Questions
Is chocolate with white streaks safe to eat?
Yes. Both fat bloom and sugar bloom are cosmetic. The chocolate may taste a little less smooth, but it's safe, and it's perfect for baking, where it gets melted anyway.
How can I tell fat bloom from sugar bloom?
Rub it with a finger. Fat bloom feels slightly greasy and smears or melts away. Sugar bloom feels dry and dusty, doesn't melt, and a drop of water dissolves it.
Can I fix bloomed chocolate?
Melt it and temper it again. Re-tempering rebuilds stable cocoa butter crystals, so the chocolate sets glossy and snappy.
What is the best way to store chocolate?
Keep it well wrapped, in a cool, dry, dark place at about 15–18 °C / 59–64 °F. Avoid the fridge unless your kitchen is very warm, and bring chilled chocolate back to room temperature before unwrapping.