What Is Chocolate Bloom?
The short answer
Bloom is the dull white or gray film, streaks or spots that show up on the surface of chocolate. There are two kinds. Fat bloom comes from cocoa butter, or from oil in a filling. Sugar bloom comes from sugar at the surface that moisture dissolves and then leaves behind as crystals when it dries.
Both are changes in the fat or sugar already in the product, not mold. Mold is rare on chocolate but not impossible, and fillings carry more of the risk, so a spot on a filled bonbon is a separate question.
How to tell them apart
Fat bloom feels smooth. It can look like anything from a dull gray film to streaks or large white spots. You’ll often read that it melts away under a warm finger, but that’s a rule of thumb, not a documented test.
Sugar bloom feels dry and rough, and tends to look dusty or blotchy. Color alone doesn’t reliably tell the two apart.
What causes it
Fat bloom follows poor tempering, storage that swings between warm and cool, or oil moving out of a nut filling into the shell.
Sugar bloom follows condensation. The classic case is chocolate taken out of the fridge into a warm, humid room. Water settles on the surface, dissolves some sugar, then evaporates and leaves the sugar behind as fine crystals.
Whether bloomed chocolate is still worth eating, and how to bring it back, is covered in the full article.
Where you’ll see it
On bars left in a warm car or pantry, on homemade bonbons a few days after making, and in the storage advice printed on chocolate packaging.
Related terms
Fat bloom and sugar bloom have their own short entries in the glossary list, as does fat migration. Prevention starts with tempering, and the crystal side of fat bloom is explained under cocoa butter polymorphs.