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With its rich, luxurious taste, chocolate has become one of the most popular foods in the world from its humble beginnings in the jungles of central America.

Now scientists have for the first time been able to examine the complex molecular structure of chocolate as it changes over time using x-rays.

The study helps to explain why chocolate produces such a divine sensation on the tongue, but also promises to help improve the quality of chocolate in the future.

Scientists  used high-powered x-rays to study the physical structure of chocolate at different temperatures. The image above shows how fat, marked yellow, can flow between crystals even at room temperature

The researchers found that even at room temperature up to a quarter of the fat molecules in a bar of chocolate are already in a liquid state – helping to produce that luxurious feel in the mouth.

Their study has also provided an insight into how chocolate can break down over time.

While in most households a bar will rarely be left lying around long enough, chocolate can, if stored too long or incorrectly, develop an unsightly white layer known as fat bloom.

Although harmless, fat bloom is one of the most common causes of customer complaints and can cost the chocolate industry millions every year.

Researchers at the Hamburg University of Technology used high-powered x-rays to watch the movement of liquid fats through the chocolate that lead to the problem.

They found that cocoa butter in chocolate bars can form any of six different crystal forms depending on how it is cooled after melting.

The scientists say that simple changes to the way chocolate is initially cooled and then stored could help to reduce the problem of fat blooming.

Nestle, one of the world's largest chocolate manufacturers which was also involved in the research, said it hoped to use the findings to improve the quality of chocolate.

Dr Svenja Reinke, a food scientist at the Hamburg University of Technology who led the research, said chocolate appears to be very sensitive to fluctuations in temperature.

She said: 'Just a few degrees make a big difference. At 5 degrees, basically, all cocoa butter is solid; and above about 36 degrees everything is liquid.'

She said that it may be possible to reduce fat blooms by changing how porous the chocolate is by altering the structure of the crystals that form.

Chocolate is extremely sensitive to heat and researchers say 18°C is the perfect temperature for storing bars

The image above shows the white fat crystas that can form on the surface of chocolate if stored in correctly

'One consequence might, for example, be to reduce the porosity of the chocolate during manufacture, so that the fat migrates more slowly.

'Another approach is to limit the amount of fat that is present in a liquid form by storing the product in cool, but not too cold, conditions. 18°C (64°F) is ideal.

'Cocoa butter crystallises in six different crystal forms. The amount of fluid also depends on the form of the crystals.'

The scientists, whose work is published in the journal Applied Materials and Interfaces, used the PETRA III x-ray source at the DESY particle accelerator in Hamburg.

The image above was created using the results of the x-rays to reveal the inner structure of chocolate as it forms from its ingredients - cocoa, sugar, milk powder and cocoa butter (shown in yellow in the image)

The results of the study could now be used to help manufacturers improve the chocolate they sell

The machine allowed them to monitor the changes occurring in the chocolate made up of different mixtures of cocoa, sugar, milk powder and cocoa butter in real time.

The x-rays allowed them to examine the structure of the chocolate down to a few nanometres.

Dr Stephan Roth, head of the beamline at PETRA III, said: 'For the first time, we have been able to track in detail the dynamic mechanisms that lead to the creation of fat bloom.'

Nestle now hopes to use the results to improve its chocolate and even produce new varieties that are more stable at different temperatures.

If stored for too long or at the wrong temperature white fat crystals can form on the surface, as shown above

Professor Stefan Palzer, assistant vice president for research and development at Nestle, said: 'Even though fat bloom does not actually constitute any deterioration in the quality of the product, the visual alteration associated with it can lead to a large number of consumer complaints.

'This is why fat bloom continues to be one of the most important quality defects in the confectionary industry.

'The experiments that have been conducted allow us as manufacturers of quality chocolate to draw conclusions concerning the root causes of lipid migration leading to blooming.

'These findings provide a solid foundation for developing suitable methods for avoiding one of the most important quality defects in the food industry.'