What does tempering chocolate actually do?
It forces cocoa butter to crystallise in one specific form out of six possible ones — and that single structural choice determines whether chocolate snaps, shines, melts at body temperature and keeps, or whether it is dull, soft and crumbly.
The underlying fact. Cocoa butter is polymorphic: it can solidify into six different crystal structures, conventionally numbered I to VI, each with a different melting point and stability. Only form V gives good chocolate — a firm snap, a glossy surface, contraction on cooling that releases it from a mould, and a melting point just below body temperature, which is why good chocolate melts in the mouth and not in the hand.
Left to itself, cocoa butter does not choose form V. It forms a mixture dominated by less stable crystals, producing chocolate that is soft, dull, fingerprints easily and develops bloom quickly.
What tempering does. It manipulates temperature to create form V seed crystals and destroy the others, then uses those seeds to direct the whole mass as it sets.
The standard sequence for dark chocolate, with different figures for milk and white:
Melt fully, to around 45–50°C, destroying all existing crystals.
Cool to around 27–28°C, at which point many crystal forms develop, including form V.
Reheat gently to around 31–32°C, which melts the unstable lower-melting forms and leaves form V intact.
Hold at working temperature while using it.
The seeding method, which is simpler: melt, then stir in solid tempered chocolate, which supplies form V crystals directly.
How to tell it worked: it sets within minutes at room temperature, snaps cleanly, shines, and releases from a mould.
Bloom, and the two kinds:
Fat bloom — grey streaking from unstable crystals reorganising or from fat migrating, caused by poor tempering or warm storage.
Sugar bloom — a gritty white surface from moisture dissolving sugar which then recrystallises, caused by condensation, typically from refrigerating chocolate.
Both are harmless to eat and indicate storage or tempering failure.
Compound chocolate, using vegetable fat instead of cocoa butter, needs no tempering — which is why it is used for decorations.