What makes chocolate so … moreish?

The Easter Bunny is back in the hutch for another year. So how are you going getting over the seasonal chocolate overdose? Craving more? That’s not surprising – here’s why.

Key Points

  • Cocoa fats become liquid at precisely 36.4 degrees Celsius
  • At this temperature, chocolate becomes ‘plastic’
  • This melt-in-your-mouth quality relies on the correct crystalline structure of cocoa fat

Anticipating the joy ahead, you slip a chocolate in the mouth and … yep … there it goes! In seconds it turns from hard to softy to gooie to liquidy to … yummie?

Our investigative friends at ABC Science have taken on the onerous task of finding out why and how.

Did you know chocolate or cocoa fats become liquid at precisely 36.4 degrees celsius? That’s a key fact for understanding what your mouth knows instinctively.

Fats ain’t fats

Cocoa fats, unlike other fats, hold their shape for some time, if kept at the right temperature. But at 36.4 they become more plastic, then liquid.

This special property is due to the crystalline structure of the solid cocoa fats.

Crystalline refers to the way the solid fat molecules are packed in a regularly ordered, repeating three-dimensional pattern.

This pattern affects the properties of the substance.

For cocoa butter there are at least six different crystalline structures, and they each have different melting points.

The sweet spot

The desired crystalline structure of cocoa fat for chocolate making is the so-called "beta prime" state.

So, when you put chocolate on your tongue it doesn't melt slowly, it just melts completely, and you feel that liquid sensation.

To achieve this, a chocolatier must first remove all the other crystalline states, through a process known as tempering.

The first step is to melt the chocolate, to destroy all the cocoa butter crystals present.

Then the chocolate is cooled very precisely, to just below that magic 36.4C.

That way the ideal beta prime crystals can solidify, but other crystalline states, which have lower melting points, cannot form.

Once the undesirable crystalline states are removed, the chocolate can then be cooled and poured into moulds.

As it sets, the beta prime crystals act as a seed, driving the rest of the chocolate to also form a beta prime structure.

Once fully crystallised, a process that can take several weeks, the chocolate has a glossy appearance, snaps crisply, and has that melt-in-the-mouth feel.

What about marshmallows?

And so, to another sweet-tooth mystery: which method of roasting gives you the tastiest marshmallows?

It is common to cook marshmallows over open flames, but variable temperatures and shifting flames can increase the likelihood of creating a flaming ball of sugar.

For the best flavours, a lower temperature of 140C to 160C is key.

In this range of temperatures, the marshmallow's sugars react with its proteins, giving a rich brown colour and complex flavours.

This is the same chemical process that makes toast, barbecued meat and hot chips taste so good.

However, above 160C another reaction, caramelisation, is more likely to occur.

This only involves sugar, and while it initially leads to a satisfying golden colour and fruity, nutty and buttery flavours, it will eventually lead to charring.