Fat bloom and sugar bloom: telling them apart

A soft grey-white film with a slightly greasy feel, often blotchy rather than even. It is cocoa butter: unstable crystal forms converting toward the more stable Form VI over time, and pushing fat to the surface as they do.

It is caused by poor tempering, by warm storage, or simply by age. A bar that was never properly tempered will bloom within weeks; a well-tempered one stored cool can go a year or more.

It is reversible in the sense that remelting and re-tempering the chocolate removes it entirely — though not, of course, on a bar you want to keep whole.

A rough, gritty, chalky white crust, usually more even and less greasy than fat bloom. Running a finger over it, it feels sandy where fat bloom feels slick.

It is caused by moisture. Condensation dissolves surface sugar, and when the water evaporates the sugar recrystallises as visible crystals. The classic cause is chocolate moved from a cold fridge into a warm room.

Remelting does not remove it in the way it removes fat bloom, because the sugar has physically migrated and recrystallised at the surface — melting redistributes it but the water damage to the surface texture has already happened.

This matters more than the distinction between them. Bloomed chocolate is not mouldy, is not unsafe, and has not gone off. It has lost gloss, snap and some textural quality.

It melts and bakes perfectly well, which is the right use for it. A bloomed bar in a brownie is indistinguishable from a fresh one.

For fat bloom: temper properly, and store at a stable 15–18°C. Temperature *cycling* matters more than the absolute number — a cupboard that swings between 16°C and 26°C daily blooms chocolate faster than a steady 22°C.

For sugar bloom: keep humidity low and avoid the fridge. If the fridge is unavoidable in a hot climate, wrap airtight and let the chocolate return to room temperature still sealed, so condensation forms on the wrapper.