The science of melting chocolate

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Share this infographic with your students, download the poster for your classroom and get students developing their knowledge of changes of state and mixtures

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This infographic is designed to be displayed as a poster in the classroom, although it could also be displayed on a projector or printed out as a handout.

Use the accompanying fact sheet and activity to explore cooling ranges of mixtures and develop graphing skills. It also offers an alternative context to the stearic acid practical and is a great opportunity to apply that learning to a new set of data.

Poster as pdf (A4 single pages or A3 one page)
Fact sheet as MS Word and pdf
Teacher notes and worksheet for age range 11–14 as MS Word or pdf
Answer sheet as MS Word or pdf

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Did you know chocolate begins to melt at a temperature lower than the temperature of the human body? That’s why when you put some in your mouth it begins to melt.

So what is the melting point of chocolate? There’s isn’t an exact point. There’s a range, because it’s a mixture.

What is chocolate made from?

Cocoa is the simple answer. Cocoa comes from the seed pods of cocoa trees. The seed pods contain beans, which are fermented, roasted and processed. Other ingredients, such as sugar and milk, are added to make the finished chocolate.

Source: © Dan Bright

Source: © Dan Bright

Cocoa comes from the beans inside the seed pods of cocoa trees. These beans contain roughly 50% cocoa butter, which is chocolate’s main ingredient. Cocoa butter is made up of three fats in roughly equal amounts. The ratio of these fats strongly affects chocolate’s melting range.

To make chocolate melt in your mouth, chocolatiers try to maximise the amount of Type V fat crystals in the mixture using a process called tempering. This involves heating and cooling the mixture to melt the different crystal types (which have different melting points) until mainly Type V remains.

Crystallisation

The fats in cocoa butter can form six different types of crystal, which melt at different temperatures:

Crystallisation type	Melting point	Taste notes
Type I	17.3°C	Soft, crumbly
Type II	23.3°C	Crumbly, melts easily
Type III	25.5°C	Firm but melts easily
Type IV	27.3°C	Firmer but melts easily
Type V	33.8°C	Best for eating: melts near body temperature, crisp snap
Type VI	36.3°C	Too hard

The melting range of chocolate depends on the types of crystals that chocolatiers create in the mixture.

Did you know …?

Chocolate with Type VI crystals is sometimes used to make heat-resistant chocolate for army survival packs.

Tempering

To make chocolate melt in your mouth, chocolatiers try to maximise the amount of Type V crystals in their creations using a process called tempering. This involves:

heating the chocolate to about 40°C to make sure all the various crystal forms are melted;
cooling it gradually to 28°C to give a mixture of Type IV and Type V crystals;
heating it again, this time to 32°C to melt the Type IV crystals;
then pouring it into moulds where it sets.

Melting ranges

The mixture of ingredients in chocolate recipes affects the melting point of the finished product. For example, adding milk to dark chocolate to make milk chocolate lowers the melting point.