Short answer
The pale film is bloom, and there are two kinds. Fat bloom is cocoa butter that has melted and recrystallised at the surface in a less orderly crystal form, often after warm-cool cycles or poor tempering; it looks greasy-grey and smears. Sugar bloom is sugar dissolved by condensation and recrystallised as a dry, gritty white dust. Both scatter light and dull the gloss. Bloom is treated in the literature as a quality defect rather than a safety issue.
Cocoa butter can crystallise in six forms, numbered by stability. Form V gives chocolate its gloss, its snap and melting in the mouth rather than in the hand, so tempering — heating, cooling and reheating chocolate under control — is designed to seed it. A tightly packed, smooth form V surface reflects light specularly, like a mirror, which the eye reads as a deep, glossy brown. Anything that roughens the surface on the scale of light's wavelength breaks that reflection into diffuse scatter and the chocolate looks paler and greyer, even though its pigments have not changed.
In fat bloom, cocoa butter migrates to the surface and recrystallises there in the more stable form VI, as larger, irregular crystals. The main chemical signature of fat bloom is form VI where form V should be. It is encouraged by warm storage and temperature swings, which melt part of the fat and let it recrystallise; by cracks from cooling; by poor tempering; and by fats migrating from soft fillings such as nut pastes. Fat bloom feels greasy, tends to cover the surface or form marbled patterns, and melts away under a warm fingertip.
Sugar bloom forms when moisture reaches the chocolate surface — typically condensation after chocolate is taken from a fridge into a warm room, or storage in humid air. The water dissolves sugar at the surface; when it evaporates, the sugar recrystallises as a fine, dry, white layer. It feels rough rather than greasy and does not melt with warmth. A drop of water dissolves sugar bloom, which is one simple way to tell the two apart; researchers use Raman spectroscopy and X-ray diffraction to classify bloom precisely.
The two can coexist on one bar, and bloomed chocolate can be melted and re-tempered for cooking.
Stable, cool storage away from humidity prevents most bloom: a cupboard at a steady moderate temperature is better than a fridge. If chocolate must be refrigerated, keep it wrapped and let it come to room temperature before unwrapping so condensation forms on the wrapper rather than the chocolate. Makers prevent fat bloom with good tempering, formulation choices and barrier layers between fillings and shell. Consumers widely read bloom as a sign of poor quality, which is why manufacturers work to avoid it.
| Property | Fat bloom | Sugar bloom |
|---|---|---|
| What it is | Cocoa butter recrystallised at the surface (form VI) | Sugar dissolved by moisture and recrystallised |
| Feel | Greasy, smooth | Dry, slightly rough |
| Under a warm fingertip | Melts and smears | Does not melt |
| With a drop of water | No change | Dissolves |
| Typical cause | Temperature swings, poor tempering, filling fats | Condensation, humid storage |
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactModerate evidence
Cocoa butter has six crystalline polymorphs; form V is preferred by chocolate makers, and the presence of form VI instead of form V is the main chemical indication of fat bloom.
FactModerate evidence
Chocolate bloom can be caused by composition flaws such as fatty fillings, manufacturing errors such as poor tempering, and storage in warm or humid conditions; sugar bloom can result from moisture dissolving sugar that then crystallises at the surface.
Source: Point-of-care detection, characterization, and removal of chocolate bloom using a handheld Raman spectrometer; Chemical Composition of Fat Bloom on Chocolate Products Determined by Combining NMR and HPLC–MS
Colourwise interpretationModerate evidence
The whitish appearance of bloom is an optical effect of surface crystals scattering light diffusely instead of reflecting it specularly, not a change in the chocolate's brown pigments.
Based on: Colourwise's application of surface-scattering optics to the crystal changes described in the cited bloom studies.
FactLimited evidence
Bloom is viewed by consumers as an indicator of poor quality, and the bloom literature treats it as a quality defect.
Caveat: Colourwise did not locate an authoritative statement on bloom and food safety; chocolate stored badly may have other problems, so this page makes no safety claim.
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.