Tempering is a technique for getting chocolate to a state that makes it more desirable and usable. After tempering, the texture and appearance are improved – the chocolate is smooth, has a clean snap, a glossy appearance and a silky melt. Chocolate is tempered by controlling the heating and cooling of cocoa butter, so it crystallises into its most stable form – giving chocolate gloss, snap, good contraction and resistance to fat bloom. Compare this to untempered chocolate, which is soft, crumbly, bendy, streaky and dull.
Essentially, the process of tempering involves managing cocoa butter polymorphs, specifically form V crystals.
Cocoa butter polymorphism
The cocoa butter in chocolate is a fat that can crystallise into 6 (I – VI) different forms, known as cocoa butter polymorphism. If chocolate is correctly tempered, most of the cocoa butter should be in form V. Each form has its own melting point, stability and packing density:
- Less stable forms (I–IV) crystallise quickly but melt at lower temperatures and tend to transform over time into more stable forms, contributing to bloom and texture changes.
- Form V is the desired tempered state, giving typical eating chocolate its gloss, snap and melt‑in‑the‑mouth profile around body temperature.
- Form VI is even more stable and tends to develop during long storage; it can be associated with fat bloom and a firmer, waxier bite.
What tempering achieves
Properly tempered chocolate has:
- A shiny, reflective surface due to a highly ordered crystalline structure that reflects light evenly.
- A clean, sharp snap because the dense crystal network is rigid and breaks suddenly under stress.
- Good contraction on cooling, which helps it release from moulds cleanly.
- Better bloom resistance, because the cocoa butter is locked into stable crystals that are less likely to migrate and recrystallise at the surface.
The temperature curve and crystal control
Tempering follows a characteristic three‑phase temperature curve that is tuned to the chocolate’s cocoa butter profile and milk‑solids content.
- Complete melting (disordering)
- Chocolate is first heated to a temperature high enough to melt all existing crystals, typically around 45–50 °C for dark chocolate and slightly lower for milk and white.
- This erases the crystal memory, eliminating residual form IV and V, so the system can be rebuilt in a controlled way.
- Cooling and pre‑crystallisation
- The melt is then cooled into a range where crystals can nucleate rapidly, typically around 26–29 °C, depending on chocolate type.
- In this zone, numerous small nuclei form; both desirable form V and less stable polymorphs can appear, and agitation helps distribute them evenly.
- Reheating to working temperature
- The chocolate is gently reheated to a slightly higher working temperature (about 31–32 °C for dark, 29–30 °C for milk and 28–29 °C for white).
- These temperatures are carefully chosen to melt unstable low‑melting crystals (forms I–IV) while preserving form V seeds, leaving a fluid dispersion of stable crystals ready for use.
The narrowness of these ranges reflects the small melting‑point differences between polymorphs and the sensitivity of nucleation and growth rates to temperature.
Nucleation, growth, and seeding
Tempering is a classic example of controlled nucleation followed by crystal growth in a fat matrix. The key microscopic events are:
- Nucleation: As the chocolate is cooled, regions of triglycerides organise into tiny ordered clusters, which act as nuclei. The level of undercooling (how far below the equilibrium melting temperature the system is brought) strongly affects nucleation rate and crystal size.
- Crystal growth: Once nuclei form, additional molecules attach to their surfaces, building a continuous network that thickens the chocolate and eventually leads to solidification.
Practical tempering methods exploit these principles:
- Seeding method: Finely chopped, already‑tempered chocolate (rich in form V) is added to melted chocolate to provide ready‑made crystal templates. These seeds lower the energy barrier for nucleation and bias the system toward form V without excessive undercooling.
- Tabling (marble slab) method: Part of the melted chocolate is spread on a cool surface and worked until it thickens, building up crystals, then recombined with warmer chocolate. This creates and disperses an abundance of small, stable crystals while relying on mechanical shear to control growth.
In both cases, agitation is crucial: it breaks up growing crystals, distributes them through the mass, and prevents a few large clusters from dominating, which would lead to a grainy texture.
Bloom, microstructure and modern perspectives
Fat bloom—the whitish, streaky surface sometimes seen on stored or poorly handled chocolate—is caused by cocoa butter migration and recrystallisation into more stable forms at the surface. Even when the polymorph is nominally in form V, microstructural inhomogeneities can still promote bloom and mechanical weakness.
This view emphasises that getting to form V is necessary but not sufficient; the way crystals nucleate and grow and the resulting network uniformity are just as important. Variations in cocoa butter composition due to origin, processing, or formulation changes can shift ideal tempering curves, which is why manufacturers often specify brand‑ or couverture‑specific temperature bands.
In summary, tempering is the macroscopic expression of the physics of precise temperature control, deliberate seeding, continuous agitation and appropriate cooling, to yield a dense, fine and uniform form V crystal network that gives chocolate its characteristic gloss, snap and melt.