A pale film on chocolate is neither mould nor a sign that it has gone off. It is either cocoa butter that has migrated to the surface, or sugar crystals left behind after moisture evaporated. Two different faults with opposite causes: the first from heat, the second from water. You can work out which one you have in seconds.
Telling them apart by touch and by eye
| Sign | Fat bloom | Sugar bloom |
|---|---|---|
| Appearance | Soft greyish-white streaks, often patchy | Fine glittering crystals, evenly spread |
| Touch | Smudges under a finger, surface feels greasy | Rough, slightly gritty |
| Warmed in the hand | Disappears, the surface turns glossy | Stays |
| Taste | Unchanged | A faint grittiness |
The most reliable check is to rub it with a finger. Fat bloom dissolves in the warmth of your hand; sugar bloom is going nowhere.
Where fat bloom comes from
Cocoa butter in chocolate exists in several crystal forms. Properly tempered chocolate is made of form V, but that is not the most stable one: over time the fat tends to move to form VI, denser and higher-melting. During that transition part of the fat migrates to the surface and crystallises there in large crystals that scatter light.
What speeds it up:
- Temperature swings. Storage at 25 °C by day and 18 °C at night drives fat to the surface far faster than a steady 22 °C.
- Faulty tempering. If there was little form V to begin with, the transition takes days rather than months.
- Fillings with foreign fats. Nut paste, praline, coconut oil — their fats migrate into the chocolate shell and displace cocoa butter outward. This is the commonest cause of bloom on bonbons specifically, as opposed to bars.
- A shell that is too thin. The thinner the wall, the sooner fat from the filling reaches it.
Where sugar bloom comes from
The mechanics are completely different. Moisture condenses on the surface of the chocolate — out of the air, or through a temperature change. The water dissolves sugar from the surface, then evaporates, and the dissolved sugar is left behind as crystals.
The classic scenario: bonbons taken out of the fridge and left uncovered in a warm room. The cold surface is covered in condensation instantly — and an hour later it carries sugar bloom.
The second scenario is storage above 60 % relative humidity, especially in packaging that does not seal.
What can be fixed and what cannot
Fat bloom is reversible. Melt the chocolate completely, temper it again and re-cast. That restores a bar entirely.
With finished bonbons it is harder: you cannot re-temper the shell without destroying the filling. A bloomed bonbon can only be eaten — it is safe and tastes almost unchanged, but it is not going on a display.
Sugar bloom is irreversible in every form. The sugar has already come out of solution, and re-tempering will not dissolve it: it will stay as grains in the mass. Such chocolate goes into a ganache, a filling or a batter, where the crystals will disperse in the liquid phase.
How to store it so it does not happen
Three conditions, all three compulsory.
Temperature 16–18 °C, steady. A fridge is not suitable for chocolate: it is both colder than needed and above 80 % humidity.
Humidity below 55 %. Sealed packaging handles this even in a damp room.
No swings. If bonbons have been kept cold, bring them up to room temperature without unwrapping — the packaging takes the condensation and the chocolate warms up dry. That takes two to three hours.
How long a bonbon lasts
The life of a filled bonbon is set not by the chocolate but by the filling: its moisture and its water activity. A dark chocolate shell keeps for months on its own, but the ganache inside sets the real limit — usually two to four weeks.
So bloom most often appears not because storage was wrong but because the bonbon simply outlived its own construction. How to build a ganache that lasts longer is a separate piece.
Working with shells and fillings is covered across the chocolate and bonbon masterclasses.