The Perfect Chocolate for the Perfect One


Valentine’s day is near! Get your heart shape chocolate ready and show your boo how much you love him/her.

The perfect chocolate has a smooth and shining look, snaps easily, and melts in your mouth. To make the perfect chocolate, you need to meticulously control the melting and cooling process.


It may surprise you that chocolate is a crystalline material. Actually, many common objects like copper, gold, and table salt are all crystalline.

To be counted as crystalline materials, it does not have to be shinning or “crystal-like”, it only needs to have highly ordered microstructures. In metals, atoms are stacked together in a pattern. As shown in this microscopic picture of gold, each individual white dot represents a gold atom.

ImageForArticle_4333(1).jpgMicroscopic image of Au (source:

There are many different ways atoms can be orderly arranged. They can be packed in squares, triangles, or hexagons, and each pattern represents a phase. Crystals with different phase have different macroscopic properties: melt temperature, mechanical property, optical property, etc.


Chocolate with the wrong phase melts in your hand, instead of in the mouth. It also doesn’t snap properly, and have a matte finish.

The most common tell that the chocolate is in the wrong phase is chocolate blooming, which you see the chocolate has a milky skin.

ChocolateBloom_grande_2588b339-66d8-4ed6-92ca-5fc1cddbf60d.jpgchocolate blooming (source:

So why do we have different phases, if it is just the same base atoms? The answer is in the balance between thermodynamics and kinetics.

Turns out at different temperatures, the atoms have different preferred arrangement, aka phase.  But they don’t all get to be at the preferred arrangement, because as temeprature decreases, atoms lose their mobility, and are locked into the atomic arrangement at higher temperature.

Quenching_large.JPGsteel quenching (scoure:

Sometimes, the atomic arrangement at higher temperature gives us desirable property and we want to preserve that. In the case of sword making, the glowing hot sword is qunched into cold water to quickly lower the temperature.  We want to preserve the higher temeprature phase because steel with that phase is mechanically stronger.

For the case of chocolate, the higher temperature phase structure is not desirable. The process of melting chocolate and cooling it down to the correct crystal phase is called tempering, during which the chocolate is slowly heated up over a bowl of hot water steam to melt, and then spread on to marble table top to cooled down with a median speed. chocolate on marble top (source:

The water steam keeps the temeprature steady at 100˚C. If the temp is too high, the milk and fat seperate out from the chocolate. After melting, the marble top drops the temeprature of the chocolate in the desirable rate for the correct crystal phase to form.

If the chocolate is not heated or cooled property, it will blooms, and the texture of chocolate will either be too tough or too soft.

If you haven’t got the perfect one, at least you got the secret for the perfect chocolate! Happy Valentine’s day everyone!






Published by

Huang Zhuojun

I'm a Ph.D. student, studying Materials Science and Engineering at Stanford University.

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