Revealed: What makes chocolate turn white

There's nothing more comforting than a silky bar of chocolate - but every year, millions of dollars worth of bars go to waste because they become speckled with what looks like white powder.

Now it can be revealed that this strange phenomenon is due to the fat particles in the chocolate rising to the surface - and it's all down to the temperature we store our treats at.

Keeping chocolate in too cold or too warm a place will make the so-called "fat bloom" appear, which leads to thousands of customer complaints every year, according to the UK's Channel 4 series Food Unwrapped.

Co-presenter Jimmy Doherty investigates the cause of this white bloom on tonight's show, and finds out that scientists have only recently discovered how the white speckles appear on the chocolate's surface.

Using the world's biggest X-ray at a factory in Hamburg, Germany, technicians discovered that the white powder rises to the surface through tiny cracks in the chocolate, which occur when a bar hasn't been stored at the correct temperature.

The show later reveals during a visit to the Lindt factory in Switzerland that it's best to keep chocolate stored between 14 and 18 degrees Celsius to protect it from bloom.

Fat bloom isn't harmful and a chocolate bar is still edible even if you can see white specks on it.

Scientist Dr Stephen Roth explained to Jimmy how fat bloom appears on chocolate.

He said: "Crystalline fat melts and the fat can start moving via the cracks.

"This is where the fat can go into and then it goes to the surface."

Fat bloom is the biggest cause of customer complaints and costs the chocolate industry millions of dollars every year.

Chocolatiers are working on ways to prevent bloom from occurring.

The best solution at the moment is to precisely temper the chocolate which creates the perfect crystalline conditions, making it more difficult for the fat to separate and form bloom.

However Lindt's chocolatiers say the ultimate way to prevent bloom is simply to eat the chocolate quickly before it has a chance to form.