Nestlé-sponsored research provides answers on chocolate fat bloom

The white specks from fat bloom are made up of fats and are edible, but it still changes the chocolate’s appearance and texture. Chocolate blooming is mostly related to the migration of lipids to the surface followed by subsequent re-crystallization.

The study published in ACS Applied Materials & Interfaces​ by Svenja K. Reinke and scientists from Germany’s Institute of Solids Process Engineering and Particle Technology, Germany’s national research center DESY and Nestlé, concluded that “the mechanism for lipid migration in chocolates probably involves both capillary rise … and molecular migration”.​

Consumer complaints and sale losses​

Reinke told ConfectioneryNews: “We tried to understand how (which pathway) and why (driving force) lipids migrate through chocolate. Thereby, we want to find out if and how this migration is linked to the formation of fat blooming of chocolate, which is a major quality issue in the confectionery industry. By better understanding the mechanisms of migration in chocolate it finally might be possible to slow down this process and thereby reduce chocolate blooming”​.

Some of the main consequences of chocolate blooming include high rates of consumer complaints and large sales losses for the food industry. Many food products, such as chocolate, confectioneries, and bakery products, are multi-component materials consisting of microscopic particles embedded in a continuous matrix, explained the authors.

Nestlé provided chocolate model samples​

While previously fat and oil migration in chocolate were primarily researched on a macroscopic level, the new study investigated oil migration using synchrotron microfocus small-angle Xray scattering (μSAXS), which reveals structural changes in the nanometer range, allowing researchers to obtain insights into microscopic and molecular processes during oil migration into chocolate.

With the help of DESY’s x-ray source PETRA III, the scientists have now been able to observe the underlying processes in real time. To do so, they investigated the behavior of different mixes of chocolate components, including cocoa, sugar, milk powder and cocoa butter.

The powder materials and cocoa butter were provided by Nestlé Product Technology Center in York, while four different chocolate model samples were also used, including a pure cocoa butter (Nestlé PTC) bulk sample, cocoa butter/cocoa powder (Bensdorp, Germany), cocoa butter/skimmed milk powder (Nestlé PTC), and cocoa butter/sucrose (Sweet Family Nordzucker Puderzucker, Germany).

Reducing pores and cracks​

The researchers investigating the microscopic structural changes that occur when chocolate blooms found that the lipids that are responsible move through pores and cracks in the chocolate.  Along the way, they soften and dissolve solid cocoa butter into a liquid form. The researchers say reducing the number of pores and the liquid cocoa butter content of chocolate could help minimize blooms.          

Researchers concluded that oil is first migrating through pores and cracks in the solid structure probably driven by capillary pressure. Subsequently, chemical migration through the fat phase takes place, inducing softening and partial dissolution of the crystalline cocoa butter.

“We observed that oil is migrating into the porous system of the investigated samples within seconds and that it partly came to dissolution of cocoa butter over a longer time period in that study, which might be avoided by a less porous structure and a reduction of liquid fat content. Research is going on to understand what that means for fat bloom formation and implementation for the confectionery industry,”​ explained Reinke.

Temperature sensitivity ​

The observations allow the food industry to develop specific approaches for reducing fat bloom, announced DESY in a release. “One consequence might, for example, be to reduce the porosity of the chocolate during manufacture, so that the fat migrates more slowly,”​ explains Reinke. “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 degrees Celsius is ideal.” ​

Chocolate is very sensitive to fluctuations in temperature. “Just a few degrees make a big difference,”​ Reinke noted in the release. “At 5 degrees, basically, all cocoa butter is solid; and above about 36 degrees everything is liquid.” ​On top of this, the type of crystals in the chocolate plays an important role. “Cocoa butter crystallizes in six different crystal forms,” ​explains Reinke. “The amount of fluid also depends on the form of the crystals.”​ Manufacturers can also limit fat bloom by controlling crystallization.

As regards the following steps in this research, the focus is now on the behavior and movement of lipids in real chocolate products that are present in the market. Reinke told ConfectioneryNews: “We now want to understand migration mechanisms in real chocolates. Therefore, we [need to] investigate the migration process on different scale levels to get an overall picture of the mechanisms.” ​

Source: ACS Applied Materials & Interfaces
Published ‘Vol. 7, Issue 18, pp. 9929-9936’ (2015), doi: 10.1021/acsami.5b02092​
“Tracking structural Changes in Lipid Based Multicomponent Food Materials due to Oil Migration by microfocus Small-Angle X-ray scattering”
Authors: S. K. Reinke, S. V. Roth, G. Santoro, J. Vieira, S. Heinrich, S. Palzer