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7 July marks World Chocolate Day, and is there a better way to celebrate than eating one of your favourite bars?

����ý Bitesize thinks so – by studying it, of course. We’re not just talking taste-tests, either: chocolate can be used to study melting points, state changes and even be a means to measure the speed of light.

So put on your lab-coat and grab a wooden spoon, because chocolate truly is a science – and that’s Professor Willy Wonka to you.

Temper, temper: It can teach you about crystals

Have you ever noticed that white stuff putting you off your old bar of chocolate? This stuff is known as bloom and it's completely harmless (although mould can also grow on chocolate, so if you see or smell something not quite right with it, don't to eat it.) What’s happened to your bar is it has softened at some point, separating the cocoa butter from the oils and sugars, and then solidified again, forming tiny crystals of fat on the outside – this is bloom.

The low melting point of chocolate is a very exciting property. Using a technique called tempering, you can heat and cool the chocolate to give it different characteristics by influencing how these crystals rearrange their structure. The science-y word for a structure that has the ability to change is known as polymorphism. Fat from cocoa butter can change structure into six different crystalline forms via melting, and this changes the appearance or even the sound of the chocolate.

For example, to get that anti-crumble 'snap', tempering is needed, but rapid cooling of molten chocolate provides a smoother texture. Different cooling techniques also affect the glossiness and taste, and can even prevent bloom by increasing the melting point, so it melts in your mouth but not your hands.

A light snack: You can use it to measure the speed of light

Chocolate and the speed of light may not sound immediately related, but hear us out.

By melting a big bar of chocolate for a short time in a non-rotating microwave (ask an adult to help you), you can measure the distance between the melted points, and use this to work out half the wavelength of the microwaves. There will be points where the chocolate is less melted because of the oscillations of the travelling wave.

Using this and the frequency of the microwave (for most machines that's 2.45GHz), you can use the equation Speed = Wavelength x Frequency to calculate the speed of the microwaves, which should be the same as (or very close to) the speed of light. Whoever said chocolate wasn’t a light snack?

A different kind of temper: It could teach us more about mood

You may have heard of the mood-boosting effects of chocolate in the form of releasing endorphins and dopamine, which the brain creates to help relieve the effects of stress and pain. But further research has identified that increasing certain compounds in chocolate might even spark feelings of calm.

Polyphenols are a kind of antioxidant present in things like olive oil, green tea and many fruits and veg. These are known to slow cell damage and reduce inflammation, as well as other benefits. Dark chocolate is a substance known to be rich in antioxidants and has been reported to have positive effects on mood, including calmness.

Before you use this excuse to stock the house, however, it’s important to know that many things in the chocolate-making process can have an effect on polyphenol levels. Even storing cocoa beans before processing them or roasting them at different temperatures can affect polyphenols, as many are lost in the sun-drying process way in the early stages of chocolate-making.

Dark chocolate has the highest polyphenol content, whereas milk has much lower quantities (and, normally, more sugar too - so watch out!)

This article was published in June 2022