The white bloom that occasionally forms on chocolate costs the food industry millions as a result of rejects and customer complaints. New research aims to help manufacturers prevent blooms, by shedding light on exactly how they form.

The white layer appears when liquid fats, such a cocoa butter, migrate through the chocolate to the surface and crystallise there. It is edible, but it changes the chocolate's appearance and texture, making the product less appealing to consumers.

"Despite this well-known quality issue, comparatively little has been known until now about its root causes," commented lead author Svenja Reinke from the Hamburg University of Technology (TUHH).

Experts from TUHH, research center DESY and food company Nestlé used a technique called microfocus small-angle X-ray scattering to investigate the microscopic structural changes that occur when chocolate blooms.

"The technology used to examine the samples shows us both the fat crystals and the pores inside the product, down to a scale of a few nanometers," explained Professor Stefan Heinrich from TUHH, leader of the investigation.

The study showed that the lipids which are responsible penetrate through pores and cracks in the chocolate, altering its internal structure. This process softens and dissolves solid cocoa butter into a liquid form.

The scientists hope that their observations will allow the food industry to develop new approaches for reducing fat bloom.

"One consequence might, for example, be to reduce the porosity of the chocolate during manufacture, so that the fat migrates more slowly," Reinke commented. "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. Eighteen degrees Celsius is ideal."

The type of crystals in the chocolate also plays an important role, so manufacturers can limit fat bloom by controlling crystallisation, she added.

The findings of the research have been published in the journal Applied Materials & Interfaces, published by the American Chemical Society.