Short answer: chocolate bloom is the dull grey or white film that appears on chocolate when its cocoa butter (fat bloom) or its sugar (sugar bloom) comes to the surface and crystallises there. It is a quality defect, not a safety problem. You prevent fat bloom by tempering accurately, cooling gradually and storing chocolate cool and steady, at 18°C (64°F) or below without fluctuations; you prevent sugar bloom by keeping water away from the chocolate, above all the condensation that forms when cold chocolate meets warm, humid air.
What is chocolate bloom?
Bloom is a loss of gloss: the surface turns dull, from a grey film or marbling to small white spots or large white patches. Food scientists Lonchampt and Hartel describe it this way in their review of fat bloom (2004). Iowa State University Extension adds that bloom affects neither the taste nor the shelf life of chocolate and does not make it unsafe; it only affects how it looks. For a shop or a chocolatier that is still a real cost, because a bloomed bonbon or bar cannot be sold as a finished piece.
| Fat bloom | Sugar bloom | |
|---|---|---|
| What it is | Cocoa butter crystallising in an unstable form or at the surface | Sugar dissolved by moisture and recrystallised on the surface |
| How it feels | Smooth | Rough, dusty |
| Quick test | A spatula warmed on a 40°C (104°F) hot plate melts it | A drop of water dissolves it |
| Main causes | Poor tempering, cooling too fast, warm or fluctuating storage, fillings | Humidity, condensation, moving chocolate from cold to warm |
| Prevented by | Tempering, gradual cooling, cool and steady storage | Dry storage, sealed packaging, slow warming |
The feel comes from Iowa State University Extension; the two tests come from a 2020 study in Scientific Reports (Heuler et al.), which also found that one piece can carry both kinds of bloom. If the white film looks fuzzy or raised, it may be mold instead: read our guide to chocolate bloom vs. mold.
What causes fat bloom
Fat bloom starts in the workshop as often as in storage. Lonchampt and Hartel list these causes:
- Under-tempering: too few stable seed crystals; bloom can appear in under two days, as large white spots or white rings.
- Over-tempering: too many seed crystals; the surface is not bright out of the mould and soon turns dull grey.
- Cooling too fast: unstable crystals and fine cracks in the surface, both of which lead to bloom later.
- Warm storage: between 18°C and 30°C (64–86°F) bloom develops faster as the temperature rises; above 32–34°C (90–93°F) the cocoa butter partly melts and recrystallises out of control.
- Temperature swings: even small fluctuations speed it up; the review cites a measurable difference between chocolate kept at 24°C (75°F) and at 24 ± 1°C.
- Fillings and nuts: filled chocolates are more prone to bloom than solid ones, and the risk grows with more filling and a thinner chocolate shell. The insurers' Transport Information Service (TIS) names marzipan and nougat fillings as particularly prone.
What causes sugar bloom
Sugar bloom is a water problem. Moisture condenses on the chocolate, draws sugar to the surface and leaves it behind as fine crystals when it evaporates (Barišić et al., Molecules, 2019). The usual triggers are humid air and moving chocolate quickly from a cold place to a warm one (Abe-Inge et al., Heliyon, 2024). Iowa State University Extension notes that sugar bloom is most likely on refrigerated chocolate, and the TIS cargo guide warns that chocolate carried refrigerated at 4.4–7.2°C (40–45°F) risks condensation when it is unloaded into a warm room.
How to prevent chocolate bloom, step by step
Bloom is prevented at four points: tempering, cooling, storage and handling. Each one closes a different cause.
1. Temper accurately, every batch
Good tempering gives the largest number of the smallest crystals in the stable form, Form V, which is what gives gloss, clean release from the mould and resistance to bloom (Lonchampt and Hartel). Martellato's user manual for its Digital Meltinchoc melters (MCD101 to MCD104) sets these programs for the seeding method:
| Program | Melting | Holding (tempered) |
|---|---|---|
| Dark | 45°C (113°F) | 31°C (88°F) |
| Milk | 45°C (113°F) | 29°C (84°F) |
| White | 45°C (113°F) | 28°C (82°F) |
Your couverture's own sheet comes first when it differs: Bassan Sur del Lago 71% is melted at no more than 50°C (122°F), worked at 30–32°C (86–90°F) and used within four hours of tempering. Check every batch with a thermometer. For the full method, see our guide to tempering chocolate and the tempering troubleshooting guide.
2. Cool gradually, not cold
Cooling too fast creates unstable crystals and hair cracks, and cooling too cold can leave moisture on the pieces, which leads to sugar bloom (Lonchampt and Hartel). A 2024 study in Heliyon describes moulds cooled gradually in a cooling chamber at about 10°C (50°F); Bassan's sheet for its 71% gives a crystallisation range of 16–18°C (61–64°F). For enrobed pieces, the same review recommends that the centre be slightly warm, not cold, when it is coated.
3. Store cool, steady and dry
Keep finished chocolate cool and at a constant temperature. These are the figures the sources give:
| Source | Temperature | Relative humidity |
|---|---|---|
| Lonchampt and Hartel (2004), fat bloom review | 18°C (64°F) or below, without fluctuations | — |
| Bilait, chocolate storage cabinets | 12–18°C (54–64°F) | About 45% |
| Bassan Sur del Lago 71% product sheet | 16–20°C (61–68°F), sealed | Below 50% |
| Iowa State University Extension | 65–70°F (18–21°C), airtight, dark | Below 50–55% |
| TIS cargo guide, storage and transport | 10–18°C (50–64°F); chocolate deteriorates from 21°C (70°F) | 65–70% |
The evidence for cool storage is clear. In a 2014 Mendel University trial, six chocolate products kept at 6°C and 12°C (43°F and 54°F) showed no deterioration after ten weeks; at 20°C (68°F) fat bloom appeared on some from the sixth week, and at 30°C (86°F) all of them deteriorated clearly. For the humidity side, see our guide to the ideal humidity for storing chocolate.
4. Handle cold chocolate without condensation
Iowa State University Extension advises against storing chocolate in the refrigerator: it picks up odours and gets a moist surface when it comes back to room temperature, which causes bloom. If chocolate has to be chilled or frozen, its procedure avoids the temperature shock:
- Before freezing, put the chocolate in the refrigerator, unwrapped, for 24 hours, then wrap it well and freeze it in an airtight container.
- To use it, thaw it, still wrapped, in the refrigerator for 24 hours, then bring it to room temperature.
- Unwrap it only once it has reached room temperature.
The same logic applies to deliveries in cold weather and to pieces coming out of a cooling cabinet: let them reach room temperature in their sealed packaging before you open it.
Can you fix bloomed chocolate?
Yes, by melting it. Iowa State University Extension states that bloom is not reversible but can be remedied by melting: the fat or sugar goes back into the chocolate, and once it hardens again it has no bloom. Melting works especially well for fat bloom; sugar-bloomed chocolate must be heated with care because it may seize or turn grainy. Bloomed chocolate can also be used in baking. Re-temper it before you mould or coat with it, and look for the cause in your tempering, cooling or storage, or the bloom will come back.
Equipment that keeps bloom out of production
Each tool closes a different cause; pick by batch size and by how much of the tempering curve you want the machine to run.
| Need | Product | Price |
|---|---|---|
| Check every batch | Martellato digital thermometer 50T001 | $29.95 |
| Hold temper by seeding, small batches | Martellato Digital Meltinchoc MCD101, 3.6 L | $1,150.00 |
| Hold temper by seeding, a full shift | Martellato Digital Meltinchoc MCD102, 6 L | $1,259.99 |
| Let the machine run the whole curve, 3.5 kg | Pavoni MiniTemper 110V | $3,350.00 |
- Digital Meltinchoc: PID control up to 50°C, an integrated probe and three pre-set programs for dark, milk and white, 110 V. You add the seed chocolate; the melter holds the temperature. Martellato table-top melters come with a free spatula.
- Pavoni MiniTemper: three-stage control (melt, crystallise, harden), five programmable presets, 20–60°C in 0.5°C steps and a 3.5 kg tank; choose it when you want the machine, not the operator, to run the curve.
- Infrared thermometer: a second check on the bench, the Martellato 50T002 → $76.50.
View chocolate melters → | View tempering machines →
For larger production, Bilait, whose machines we distribute exclusively in Canada, builds tempering machines and a vertical cooling tunnel, the Verticool 275, specified for an air-conditioned room at 45% relative humidity.
How AI can help your production
Paste the tempering and storage tables above into an AI assistant and ask it to write a one-page procedure for your team, with a line to sign the melting temperature, the working temperature, the cooling time and the storage-room temperature and humidity for each batch. When bloom appears, give it the batch records and ask which step changed. A simple log turns bloom from a mystery into a cause you can fix.
AI organises the information; tasting and the final decision stay with your chef.
Bloom-resistant production at Zucchero Canada
We are an authorized distributor of Martellato and Pavoni Italia, and we sell the couverture and cacao to go with them:
- Couverture with a clear storage spec: Bassan Sur del Lago 71%, made in Canada from Venezuelan cacao, with tempering, crystallisation and storage figures on its sheet; 5 kg bag $273.00, also in 20 kg cases.
- Bean-to-bar makers: Sur del Lago cocoa beans from Venezuela, 1.5 kg bag $80.00. Your own chocolate needs the same tempering and storage discipline.
- The reference book: Chocolate by Ramon Morató, 416 pages on tempering, coating and glazing and on bonbon fillings that resist drying and crystallisation, $160.00.
Melters and couverture are stocked in Calgary and ship across Canada; food products ship within Canada only. Orders over $500 CAD get 5% off automatically at checkout. Equipping a production kitchen or buying couverture in volume? Contact our team or call 587-774-8873 (toll free 877-741-8251).
Chocolate bloom vs. mold | Ideal humidity for storing chocolate | Does chocolate go bad? | How to temper chocolate | Chocolate melters | Thermometers
This article is for information only. Every business is different: draw your own conclusions based on your own expectations, budget and goals, and talk to qualified experts before you decide or invest.
Sources: Lonchampt P. and Hartel R.W., "Fat bloom in chocolate and compound coatings", European Journal of Lipid Science and Technology 106 (2004) 241–274; Heuler J. et al., Scientific Reports 10 (2020) 9833; Barišić V. et al., "The Chemistry behind Chocolate Production", Molecules 24 (2019) 3163; Abe-Inge V. et al., Heliyon 10 (2024) e36961; Machálková L. et al., MendelNet 2014; Iowa State University Extension and Outreach, AnswerLine, "Chocolate – Shelf Life, Storage, and Bloom" (2023); Transport Information Service (German Insurance Association), "Chocolate"; Martellato, Digital Meltinchoc user and maintenance manual; Bilait catalogue 2026 and Verticool 275 datasheet; Bassan Chocolate, Pavoni Italia and Martellato product data.
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