Chocolate Tempering Science: Why Cocoa Butter Crystal Form Changes Everything

Melt a piece of good chocolate, pour it onto parchment, and let it set at room temperature. What you’ll get is a dull, soft slab that crumbles rather than snaps, and probably develops white streaks within a day. That’s not bad chocolate. That’s physics.

The chocolate was fine before you melted it. What changed is the crystal structure of the fat, and this is entirely reversible if you understand the process.

Cocoa Butter’s Six Personalities

Cocoa butter is the fat extracted from cacao beans. It makes up about 30-35% of a typical dark chocolate bar. Unlike butter or lard, which are mixtures of many different triglycerides with a range of melting points, cocoa butter has a relatively narrow fatty acid composition. It’s predominantly oleic, stearic, and palmitic acid, in specific arrangements.

This uniformity makes cocoa butter polymorphic in a remarkably structured way. It can crystallize into six distinct forms, labeled Form I through Form VI (sometimes labeled I-VI or using Greek letters in older literature). Each form has a different melting point and different crystal geometry.

Form I melts around 61°F (17°C). Form VI melts around 97°F (36°C). The forms in between span that range. What makes Form V special is that its melting point (around 93-95°F, 33-35°C) is just below body temperature. That’s why good chocolate melts cleanly on the tongue and not in your hand.

Think of the six forms as six different ways to stack the same furniture in a room. Most arrangements are unstable and will shift over time to something more stable. Form VI is the most stable arrangement, but it melts too high (you’d feel wax, not chocolate) and takes weeks to form naturally. Form V is the kinetically favored stable form at the right temperatures, meaning it forms reliably with correct technique and persists for months without converting further.

The Physics of the Snap and Shine

Form V crystals are small, dense, and pack uniformly. That dense packing is physically hard to deform without fracturing, which produces the characteristic sharp snap when you break a well-tempered bar.

The gloss comes from the crystal surface. Uniform Form V crystals produce a smooth surface at the microscopic level. Light reflects evenly from a smooth surface, giving the bright, mirror-like appearance. Less uniform crystal forms create a rough surface that scatters light in all directions, appearing dull or matte.

Contraction is also a Form V property. As Form V crystals form during cooling, the cocoa butter contracts slightly. This is what allows chocolate to release cleanly from molds. Untempered chocolate sticks to molds because it doesn’t contract.

The Temperature Curve

Tempering dark chocolate requires three temperature stages, each with a specific purpose.

First, melt to 115-120°F (46-49°C). At this temperature, all six crystal forms melt. The cocoa butter is fully liquid and crystal-free. If you skip this step and don’t fully clear the previous crystal structure, old crystals of wrong forms will seed new crystal growth and your temper will be wrong from the start.

Second, cool to 80-82°F (26-28°C). At this temperature, multiple crystal forms can nucleate, including Form V. Stirring constantly is critical. Stirring does two things: it keeps temperature uniform throughout the chocolate (cocoa butter cools from the outside in, and the edges can drop too far if not mixed), and it promotes crystal nucleation by creating mechanical disturbance in the crystallizing fat.

Third, reheat gently to 88-90°F (31-32°C). This is the working temperature. Reheating melts the less stable Form I through IV crystals that formed in stage two, while Form V (which has the highest melting point of the desirable forms) survives. You’re left with a seed population of Form V crystals in fully melted cocoa butter. As the chocolate cools and sets, those seed crystals template the growth of more Form V crystals.

The entire curve needs to be precise. At 82°F you’re seeding Form IV and V together. Heat to 90°F and Form IV melts but Form V survives. Let the temperature slip to 93°F and Form V starts melting too, and you’ve lost your temper.

Seeding: The Shortcut That Works

Professional chocolatiers often use the seeding method rather than the full cool-and-reheat curve. You melt chocolate to 115°F to clear all crystals, let it cool to about 95°F, then add 25-30% by weight of already-tempered chocolate (finely chopped) to the melted chocolate.

The existing Form V crystals in the added chocolate act as seeds. They provide a template for new Form V crystallization. The added mass also cools the melted chocolate toward working temperature. Stir consistently to distribute the seed crystals and maintain even temperature.

This is faster than tabling (spreading chocolate on a marble surface to cool it) and more consistent for home use.

Bloom: When Things Go Wrong

Fat bloom and sugar bloom are two different problems that look similar: a white, streaky, or powdery coating on chocolate.

Fat bloom is a crystallization problem. It happens when Form V crystals convert to more stable Form VI crystals, which grow larger and scatter light differently. This occurs when chocolate is stored at fluctuating temperatures, when tempering was incomplete (too few Form V seed crystals to provide stable structure), or when the chocolate was stored too warm. The white appearance is from large cocoa butter crystals at the surface.

Sugar bloom is a moisture problem. When chocolate gets wet (condensation from refrigerator storage or humid conditions), sugar dissolves at the surface and recrystallizes as the moisture evaporates. The result looks similar but has a grittier texture. Touching sugar-bloomed chocolate leaves a slightly sugary residue on your fingers.

Neither bloom type makes the chocolate unsafe. Both are reversible by melting and re-tempering.

Lecithin’s Role

Commercial chocolate contains lecithin, usually from soy. Lecithin is an emulsifier that coats cocoa particles and reduces viscosity. It allows less cocoa butter to achieve the same flow properties, which matters both for cost and for handling. It doesn’t directly affect cocoa butter crystallization, but it does affect how easily tempered chocolate sets by changing viscosity during the critical cooling phase. See the food additives article on lecithin for more.

The fat crystallization principles are the same whether lecithin is present or not. Lecithin just makes the physical process of working with chocolate easier.