Why Did My Chocolate Turn White? Fat Bloom vs Sugar Bloom
On this page
Short answer: is it safe to eat?
If it’s bloom, yes. The Canadian Food Inspection Agency (CFIA) says so in one line: “Although it may affect the taste of chocolate, it is harmless and safe to eat.” It adds that chocolate with bloom “can still be eaten or used for baking.”
Sources don’t agree on the taste. CFIA says bloom may change it. Iowa State University Extension says bloom does “not affect either the taste or shelf life of chocolate” and only changes how it looks.
When America’s Test Kitchen baked truffles and cookies with bloomed chocolate, its tasters “found no differences.” So expect a dull surface, and maybe a small change in taste. Don’t expect a health problem. Other problems you can run into at home, and the guide for each, are listed in how to make chocolate at home.
The exception is a spot that might be mold, which is more of a risk in filled chocolates than in plain bars. The last section covers it.
Which bloom is it? A quick test at home
Run a finger gently over the surface. Fat bloom feels smooth, while sugar bloom leaves “a blotchy or dusty look and rough feel to the touch,” according to ISU Extension.
Don’t go by color alone. Fat bloom can range “from a uniform dull gray to a marble aspect, as well as from small individual white points to large white spots,” as a 2004 review of fat bloom research by Lonchampt and Hartel puts it. A bright white patch isn’t automatically sugar.
Where the chocolate has been is often the better clue. Sugar bloom follows water on the surface, most often after the fridge. Fat bloom follows warmth, warm and cool swings, chocolate that was never tempered, or a nut filling.
A manufacturer’s FAQ and other secondary sources say fat bloom melts away under a warm finger or a hair dryer while sugar bloom stays put. The research makes that look less clean. One older study, cited in the Lonchampt and Hartel review, found that bloom on well-tempered chocolate melted at 34°C, while the chocolate itself melted at 30°C. And on chocolate that set without tempering, some of the pale patches are areas low in fat and high in sugar rather than fat crystals, according to a 2019 University of Wisconsin thesis by Jin.
Fat bloom
Fat bloom is fat crystallizing at or near the surface. Usually that’s cocoa butter. In filled chocolates it can include oil from the filling.
What it looks and feels like
It feels smooth. It can look like anything from an even gray dullness to streaks, marbling or white dots. On chocolate that set without tempering it tends to be dramatic: Lonchampt and Hartel describe “large white spots and/or white rings surrounding a black and glossy center.”
What causes it
Nobody has fully pinned down the mechanism. Lonchampt and Hartel write that “the specific mechanisms of fat bloom still remain largely unknown.” The conditions that bring it on are much better known.
Skipped or poor tempering is the fastest route. Melted chocolate left to cool sets mostly in unstable cocoa butter polymorphs, and as they shift toward more stable forms the surface changes. Under-tempered chocolate blooms “very quickly (less than 24 h),” and in other cases “often in less than two days,” according to the review. What tempering is and why it matters covers the crystal forms in full.
Heat does the same thing to chocolate that was tempered well. Warm it enough and the cocoa butter partly melts, and when it sets again it crystallizes without control, much like untempered chocolate. Bloom follows soon after it cools. A bar that went soft in a hot car and then hardened again is a likely candidate.
Slow storage bloom is the gentle version. Well-tempered chocolate sits in form V, which is only relatively stable, and over time it can move to form VI. Lonchampt and Hartel note that bloom on well-tempered chocolate is always found in form VI, though chocolate can make that change without visible bloom. Jin’s thesis puts the usual timescale at “months or years.” Warmth speeds it up, and so do swings. In the review’s words, “even small temperature variations increase the rate of bloom formation.”
Fillings add their own oil. According to the same review, filled chocolates “are more prone to bloom than plain chocolate,” and “the higher the filling content and the smaller the chocolate part, the greater the possibility of bloom,” with the same problem when nuts go into the chocolate. In a 2024 study of hazelnut-filled pralines by Trapp and colleagues, stored at 20°C, oil moved into the shell mostly between the fourth and eighth week, and components of hazelnut oil turned up in the bloom itself.
Bloom isn’t always the first sign. In filled bars, the shell going soft and the filling going hard often limit shelf life first, as a 2021 paper by Hřivna and colleagues notes, citing earlier work by Ziegler.
Can you fix it?
You can’t wipe it off, but you can melt it. ISU Extension says bloom “is not reversible but it can be remedied by melting,” and that melting “works especially well with fat bloom.”
Melting alone isn’t the whole fix, though. Chocolate that’s melted and simply left to set is untempered chocolate, and untempered chocolate blooms within a day or two. America’s Test Kitchen saw this happen: when it dipped cookies in melted bloomed chocolate, “the chocolate took longer to set up and the bloom reappeared.” So if you want a glossy result, melt it and temper it again, following our guide to tempering at home.
If you don’t need it to look good, bake with it. CFIA, ISU Extension and America’s Test Kitchen all say bloomed chocolate is fine for baking.
Sugar bloom
Sugar bloom is sugar that water dissolved at the surface and left behind as fine crystals when it dried.
What it looks and feels like
It feels dry and rough. ISU Extension describes “a blotchy or dusty look.” CFIA describes “a white, speckled or spotted appearance on the surface.” Some sources say it looks whiter than fat bloom, but as the quick test above shows, color isn’t a reliable guide.
What causes it
Water on the surface causes it, and the usual source is condensation. Chocolate comes out of the fridge, warm air hits the cold surface, and water forms on it. Then, in the words of Jin’s University of Wisconsin thesis, “the dissolved sugar recrystallizes on the chocolate surface leaving a white layer with larger sugar crystals.” ISU Extension is blunt about where to look: “Sugar bloom is most likely to occur with refrigerated chocolate.”
It can start while you’re making chocolate, too. Lonchampt and Hartel list moisture deposited during cooling as a cause of sugar bloom in filled products, and a 2022 study of molds in chocolate by Iacumin and colleagues cites the advice to keep the cooling temperature just above the dew point so no condensation forms. At production scale, cooling and storage are covered in the bean-to-bar process, and mold temperature in chocolate molding.
Can you fix it?
Sometimes, with care. ISU Extension says melting removes the bloom but warns that “heating sugar bloom must be done with care as the chocolate may seize or change to a grainy form.”
Baking is the safe use for it. Both CFIA and ISU Extension say bloomed chocolate can go into baking.
How to stop it happening: storage and tempering
Temper well, then keep chocolate cool, dry, wrapped and at a steady temperature. The sources agree on that much. They differ on the exact numbers, so here’s what each one says.
| Source | Temperature | Humidity | Context |
|---|---|---|---|
| Lonchampt and Hartel, 2004 | 18°C or below, without fluctuations | Not given | Review of fat bloom research |
| ISU Extension | 65°F to 70°F (about 18 to 21°C) | Below 50 to 55% relative humidity | Home storage; fridge not recommended |
| Hřivna et al., 2021 | 6°C and 12°C did best; samples at 20°C began to deteriorate after 10 weeks | Not given | Filled bars, each wrapped, stored for 26 weeks |
| CFIA | “Consistently cool” | “Dry” | No numbers given |
The low end of ISU’s range sits right around the review’s 18°C, so a cool cupboard away from the oven and the sunny window is the place for most kitchens. Storage below 18°C held off storage bloom for over a year in one study the review cites. For how long chocolate keeps once it’s stored well, see how long chocolate lasts.
The fridge is where sources split. ISU Extension advises against it, because chocolate can pick up smells and get “a moist surface when brought back to room temperature.” Yet in the filled-bar study, the bars kept at 6°C and 12°C held up best. Cold slows fat bloom, and the risk the fridge brings is condensation, which means sugar bloom. If you do refrigerate, wrap the chocolate tightly and let it come to room temperature before you unwrap it. For the freezer, ISU Extension suggests 24 hours in the fridge first, a generous wrap and an airtight container, then 24 hours back in the fridge, still wrapped, before it goes to room temperature.
A few smaller things help. Chocolate covered in aluminum foil was protected against bloom in one study the review reports, and scratches on the surface make bloom more likely. For nut-filled pieces, cooler is better: in MRI studies the review describes, oil from the filling stayed near the filling at 19°C but moved up to just under the surface at 28°C.
Tempering is the other half, and Lonchampt and Hartel put it simply: “The smaller and more regular the size of seed crystals, the glossier the chocolate and the greater its bloom resistance.” Take the temperatures from your couverture packaging rather than a general chart, and check every batch with a test strip, as described in how to temper chocolate at home. The make section collects the other home guides.
Keep compound chocolate out of the same bowl. Lauric compound and cocoa butter soften each other and can bloom, as we explain in real vs compound chocolate.
It might not be bloom: other white spots
On plain chocolate, mold is rare but possible. Fillings are where it’s more of a risk. The Iacumin study explains that molds don’t usually grow in chocolate because its water activity is low (below 0.6), but it also reports a case of mold on chocolate bars, which had a milk cream filling. The authors link that growth to bloom combined with moisture from the bloom or from packaging. The sugary fillings in pralines keep most microbes out, yet that “is not always enough to prevent the growth of osmophilic yeasts, xerophilous molds and bacteria.”
ISU Extension’s advice is the one to follow: chocolate is safe to eat unless there are “signs of spoilage,” meaning an off odor, an off flavor or mold. If a filled piece smells off, don’t eat it. If you can’t tell whether a spot is bloom, throw it out.
Sources and open questions
The water drop test (a drop that beads up on fat bloom and spreads on sugar bloom): not traced to a study or an extension service.
Re-tempering bloomed chocolate: no source tests it directly. The advice above follows from the ISU Extension and America’s Test Kitchen findings.
Humidity levels and temperature gaps quoted online as the point where sugar bloom starts: none traced to a study.
Whether sugar bloom can be undone: some sources say it can’t, and we found no peer-reviewed work either way.