Why chocolate melts in your mouth, popcorn pops and how to toast perfect marshmallows – ABC News

It’s that time of the year when many of us are getting ready to feast on Easter chocolate and if you’re lucky, maybe a marshmallow or two over an open campfire. 

Or maybe you prefer sour lollies or popcorn?

Whatever your favourite treats, we’ve got some inside goss on what makes them so delicious.

What makes chocolate melt in your mouth?

It all comes down to a unique property of cocoa fats, which are quite different from other solid fats, like lard or butter.

“When you melt [solid] fats like lard, it doesn’t turn to liquid straight away, it slowly become more plastic,”  University of Melbourne food chemist Ken Ng says.

“They retain their shape for quite a long time if you keep the right temperature.”

He says at precisely 36.4 degrees Celsius, they suddenly become liquid.

What helps makes this chocolate so delicious is the crystalline structure hidden within it.(

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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,” Dr Ng says.

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

Also known as “form V”, this crystal structure gives a very sharp melting point of 36.4C.

“So [when you] put it on your tongue it doesn’t melt slowly, it just melts completely, and you feel that liquid sensation.”

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

Melting chocolate helps remove undesired crystalline states.(

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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.

Which method of roasting gives you the tastiest marshmallows?

Some people may cook their marshmallows in 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.

For the tastiest toasted marshmallow, avoid the flames. (

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In this range of temperatures, the very special Maillard reaction occurs.

Under heat, 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 — like if you go all out and cook your marshmallow over the flames — 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.

But Dr Ng says it’s not a black-and-white situation.

“In toasting marshmallows, I would suspect that both reactions are occurring.”

But if you’re after more complex tastes, the Maillard reaction is the one to go for.

Why do we like sour lollies?

Super sour lollies are divisive: some people love them, some people hate them, and some people love to hate them.

So what’s the appeal?

Love ’em or hate ’em, sour lollies use some simple science.(

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“There’s a certain thrill in having something which is super sour, but which is not going to harm you,” says Dr John Prescott, director of TasteMatters Research & Consulting.

Our taste buds serve to inform us about the food we eat, like if it’s potentially harmful, for example.

“Sourness probably means either things are unripe, or they’ve gone off,” Dr Prescott says.

But sourness can also add to the enjoyable experience of food, particularly when combined with other flavours, especially sweet.

“The combination of things which are sour and sweet at the same time is a very common combination — any fruit-based soft drink is basically an acid sugar balance, [as well as some] fruit,” Dr Prescott says.

If you push one of those two out of balance, however, then it starts to become less and less palatable.

“[The sour lolly] is not only very sour, it’s also sweet, and that sweetness engenders a liking for the overall flavour,” Dr Prescott says.

If you love sour gummy bears it could be due to the thrill of having something super sour that isn’t going to kill you.(

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But the context of the experience also drives the enjoyment, explains Dr Prescott.

As to why some people like sour lollies and others can’t stand them?

It may be due to a person’s intrinsic sensitivity to those flavours.

Or it could be a matter of exposure.

“Once you start eating something, you can develop a liking for pretty much anything,” Dr Prescott says.

“There’s really very few limits that people have.”

And why on Earth does popcorn pop?

Popping corn relies on two things. First is the strong outer coating of the corn kernel, called the pericarp, that can withstand a large amount of pressure.

Second is the inside of the kernel, known as the endosperm.

“The endosperm is rich in starch, but it has a small amount of water, about 14 per cent,” Dr Ng said.

“These structures allow corn to pop.”

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By heating the kernel rapidly to temperatures above 100C, the moisture inside quickly turns into steam and expands.

“But because the hull is very compact and does not allow the steam to pass through, you basically have a high-pressure environment inside the corn,” Dr Ng explains.

“It means that heat there will be more than just the heat of the steam, which is 100 degrees Celsius, it’s probably 115 degrees Celsius”.

At this high temperature, the solid starch grains begin to melt.

When heated the starch inside the corn grain splatters out creating the fluffiness of popcorn.(

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At a critical temperature of 180C, the pressure inside the kernel ruptures the pericarp, with a force of around 90 tonnes per square metre.

“You have this amazing effect where the starch splatters out of the corn grain into the fluffiness it has,” Dr Ng says.

“Because the starch all of a sudden is not under any pressure, [the corn grains] just expand out and dry straight away.”

Simultaneously, the steam rapidly escapes the kernel and causes a rapid pressure drop, resulting in the iconic “pop”.

And the grains that don’t pop?

This may be because of damage to the hard exterior — the hull — of the corn kernel.

“If the hull is damaged, under heat, [the steam] just escapes,” Dr Ng says.

“There is no build-up to the high pressure.”

Or it could be that the particular kernel has low water content, so not enough steam is generated to burst it.

And Dr Ng has one final tip: don’t try to dry out fresh corn to make popcorn.

“There are different varieties of corn, some better for making popcorn than others,” he says.

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