Understanding Fat Bloom
Why chocolate turns grey and dusty, and how tempering and storage keep it from happening.
Fat bloom is cocoa butter that migrated to the surface and recrystallized into unstable crystal forms. It comes from poor tempering, temperature fluctuation during storage, or both. Prevention: temper correctly, store at a stable 60–65°F, and cool freshly cast chocolate gradually. Bloomed chocolate is safe to eat and can be re-melted and re-tempered.
What fat bloom looks like
Fat bloom appears as a dull, grey-white haze or irregular patches on the surface of chocolate. In mild cases it's a faint chalky film that reduces gloss. In severe cases the entire surface turns dusty grey, sometimes with a slightly soft or waxy texture. It can appear within hours of casting (sign of failed temper) or weeks later (sign of temperature abuse during storage).
Under magnification, fat bloom looks like needle-shaped cocoa butter crystals breaking through the chocolate surface. The chocolate itself is structurally unchanged, bloom is a cosmetic and textural defect, not a sign of spoilage.
Fat bloom vs. sugar bloom
Both produce a white-grey surface discoloration, but the cause, and feel, are different.
Cocoa butter crystals on the surface
Feels smooth or slightly waxy
Caused by temperature fluctuation or poor temper
Can be re-melted and re-tempered
Sugar crystals dissolved and redeposited
Feels gritty or grainy to the touch
Caused by condensation, temperature shock from cold
Cannot be fully reversed; the texture is altered
To tell them apart: run a fingertip over the surface. Fat bloom smooths out under brief friction from body heat. Sugar bloom remains gritty, the crystals don't melt under light pressure.
Causes of fat bloom
Chocolate that was not properly tempered, or where the temper broke before casting, contains primarily unstable crystal forms (Form I–IV). These forms are metastable: they convert to lower-energy Form VI over time, causing cocoa butter to migrate and recrystallize at the surface. Bloom that appears within the first 48 hours of casting almost always traces to a tempering problem. See the tempering guide for the seed method and temperature targets.
Even properly tempered chocolate will bloom if stored in a warm environment or subjected to cycling temperatures. Cocoa butter melts partially at temperatures above 78–82°F (depending on the chocolate), then recrystallizes in unstable forms as it cools. A single trip from a 65°F pantry to a 78°F car and back is enough to initiate bloom. Cyclic fluctuation (warm days, cool nights, repeat) is more damaging than a single brief exposure.
Freshly cast chocolate needs to cool gradually and evenly to allow Form V crystals to grow uniformly. Putting molds directly in a refrigerator causes the outer surface to contract faster than the interior, creating stress that pushes cocoa butter out. A cool room at 60–65°F is better than a refrigerator for the initial set. Once fully set (30–45 minutes at room temperature), brief refrigerator time for demolding is fine.
Prevention
Can you rescue bloomed chocolate?
Fat bloom: yes. Bloomed chocolate is safe to eat, it just looks and feels wrong. The cocoa butter hasn't gone off; it's just in the wrong crystal form. Re-melt the chocolate to 50°C (fully destroying the unstable crystal structure), then re-temper using the seed method. The result will be identical to the original. This works indefinitely as long as no water or contamination entered the batch.
Sugar bloom: partially. Sugar bloom involves dissolved and redeposited sugar crystals that have changed the microstructure of the chocolate surface. Re-tempering will improve the appearance, but the texture may not fully recover. If the bloom was minor, re-tempered chocolate will be close to the original. Heavy sugar bloom (gritty, chalky throughout) is harder to correct.
Log your storage conditions alongside your temper notes. When bloom appears, your batch records help you trace whether it was a tempering issue or a storage issue.
Log a Batch →