Two squares of dark chocolate side by side on a slate, one glossy and deep brown, one streaked and dusted with whitish bloom, beside a broken bar showing a clean snap

Why Chocolate Turns White: Bloom, Safety and Storage

Published 10 Sep 20265 min read

A bar of good chocolate left in a warm car or forgotten through a summer can come out of its wrapper streaked or dusted white and gray, and it is tempting to throw it away. What is on it is bloom, the chocolate's own cocoa butter or sugar that has moved outward; it is not mold or spoilage, and it is safe to eat. Good storage goes a long way toward preventing it. Tempering, the step that sets cocoa butter's crystals, is covered in the guide to how bean-to-bar chocolate is made.

Why does chocolate turn white?

The white streaks or dust are bloom, not mold. Fat bloom is cocoa butter that separated and settled on the surface in larger crystals, usually after warm or long storage; sugar bloom is sugar left behind when condensation, often from the trip out of the refrigerator, dissolves it and then evaporates. Bloomed chocolate is safe to eat; only the gloss, and in a very old bar the texture, suffers.

The two kinds of bloom

Fat bloom is a matter of crystals. Cocoa butter, the fat in chocolate, can solidify in six different crystal forms, and only one of them, the one tempering aims for, gives a bar its gloss and its melt-in-the-mouth texture. When chocolate is stored too warm or too long, some of its cocoa butter separates and deposits on the surface, settling into larger crystals that scatter light instead of reflecting it, which shows as pale streaks and blotches. Cold slows it without stopping it: fat bloom can form at almost any temperature, though it generally forms more slowly as the temperature drops. The bar goes dull, but if the bloom is only on the surface it tastes the same.

Sugar bloom comes from moisture. If chocolate is moved from a cold refrigerator into warmer air, water condenses on its surface and dissolves some of the sugar; when the water evaporates, the sugar is left behind as tiny crystals, a white, powdery coating.

Popular Science describes chocolate as a mixture of cocoa particles, sugar crystals and, in milk chocolate, milk powder, all held together by cocoa butter, so the same two kinds of bloom can turn a milk chocolate bar white.

Fat bloom or sugar bloom: how to tell

	Fat bloom	Sugar bloom
Looks like	Grayish or whitish streaks, freckles or haze; overall dullness	A white, powdery coating
Cause	Cocoa butter separates, deposits on the surface and settles into larger crystals that scatter light	Condensation dissolves surface sugar, which is left behind as tiny crystals when the water evaporates
Typical trigger	Warm storage, long storage, or incompatible fats from a filling	Unwrapping chocolate straight from the refrigerator or freezer
Safe to eat	Yes; tastes fine if the bloom is only on the surface	Yes; still good to eat, just less pretty
Best use	Melting into brownies, ganache or drinking chocolate, or melting and re-tempering	Melting into brownies, ganache or drinking chocolate
Prevention	Cool storage; chocolate brands recommend about 57 to 61°F	Wrap well before chilling; leave wrapped until it reaches room temperature

Is bloomed chocolate safe to eat?

Yes, both kinds of bloom are safe to eat. Richard Hartel, a professor of food science at the University of Wisconsin quoted by Popular Science, says surface bloom has no effect other than the visual turn-off. Bloom that has worked deep into a very old bar is different: the chocolate turns cracked, dry and crusty, possibly with a waxy aftertaste, according to Hartel.

Baking with bloomed chocolate

Baking is a good use for a bloomed bar. Melting takes care of the crystals: once the chocolate is liquid in a brownie batter, a ganache or a cup of drinking chocolate (see the drinking chocolate three ways recipe), the crystal structure that bloomed no longer matters. The craft chocolate complete guide makes the same point. The one thing bloomed chocolate is not good for is any use where it needs to set hard and glossy again (dipping, coating, molding) unless it is re-tempered. King Arthur Baking's seeding method, below, is one way to re-temper at home with a double boiler and a thermometer.

When the bloom starts at the factory

Fat bloom can also begin on the production line. Wolfgang Danzl, a food engineering researcher at the Fraunhofer Institute for Process Engineering and Packaging in Germany, studied what happens in enrobing machines, where liquid chocolate flows like a curtain over the product. Some of that chocolate sticks; the rest flows off and is tempered again inside the machine, and it can wash some of the filling's fat along with it. Those filling fats, oils from nuts, coconut oil or palm kernel oil, are not cocoa butter, and they can muddle the organized crystal lattice of tempered chocolate, leaving it softer and more crumbly. The team found up to 10 percent filling fat in some chocolate, where half a percent to 2 percent is normal for most products. Fat bloom, in other words, is not always a sign of how a bar was stored.

How to store chocolate

Chocolate wants two things: cool and dry. Chocolate brands recommend a cool environment, ideally around 57 to 61°F, according to Popular Science. At home that means keeping the bar wrapped and somewhere cool, away from warm spots like a sunny windowsill. Cooler storage slows fat bloom, and a dry surface gives sugar bloom nothing to dissolve. In summer, or in a hot kitchen, the question becomes the refrigerator.

Should chocolate go in the refrigerator?

It can, if it is wrapped well. The danger is the trip out: cold chocolate unwrapped in warmer air collects condensation, and that water is what causes sugar bloom. Wrap it before it goes in, and leave it wrapped on the way out until it has come to room temperature, so the condensation forms on the wrapping rather than on the chocolate. The freezer follows the same rule. The shelf-by-shelf pantry storage guide covers the rest of the pantry.

Re-tempering at home

Tempered chocolate can be melted and tempered again; enrobing machines do exactly that with the chocolate that runs off. King Arthur Baking's seeding method, worked through with semisweet chocolate, melts about three-quarters of the chocolate, keeping it below 122°F, stirs in the remaining quarter as seed while it cools to 80 to 82°F, then rewarms it gently to 88 to 90°F, at which point it is tempered and ready to work with.

A dark bar such as Dandelion's Maya Mountain, Belize 70% (shop Dandelion Maya Mountain Belize 70%) is the kind to keep wrapped and somewhere cool. Products ship across the continental U.S. from theambrosianpantry.com, and the shop is at 263 Josephine Street in Cherry Creek, Denver, where visitors can ask staff questions. Once a bar is home, the rest of its life is up to the cupboard.