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  • Soft Matter, Article Reference: B. R. Pinzer, A. Medebach, H. J. Limbach, C. Dubois, M. Stampanoni and M. Schneebeli. 3D-characterization of three-phase systems using X-ray tomography: tracking the microstructural evolution in ice cream. Soft Matter, 2012. Epub ahead of print. DOI: 10.1039/C2SM00034B 

The "metamorphism" of ice cream

Why is ice cream an interesting subject for snow scientists? It is not only that scientists like to eat it but they also are interested in applying and extending the knowledge gained from less tasty regular snow and ice.

SLF has a unique setup for micro-tomography of frozen samples. In a coldroom, frozen samples of snow or ice cream can be measured at varying temperatures for several days or even weeks at a time. This in-situ study allows changes in the shape of ice crystals, air bubbles and sugar solution in ice cream to be continuously monitored. This methodology is the same as that used to observe snow metamorphism in detail (see ATGM- project site).

In a joint project with scientists from the Nestlé Research Center in Lausanne, the evolution of ice cream was investigated using tomography. Ice crystals affect the properties of ice cream, altering its texture and structure as they grow and change shape. These changes in the ice crystal structure of ice cream particularly occur when the freezer temperature fluctuates up and down a couple of degrees, causing slight melting and refreezing - a common occurrence in home freezers. Under these conditions, over time, ice cream may lose its creamy taste and texture and become coarse and chewy.

The in-situ x-ray tomography technology was used to study the structure and phases of ice cream during storage, with the aim of understanding how to maintain the product’s original texture and structure for longer. We showed that ice crystal growth was mostly influenced by the amplitude of the temperature cycle, while the coarsening of the air bubbles depended on the duration of the warm cycle. Using this technique, we gained a deeper understanding of the coarsening process of ice cream. The results of this study were published in the journal Soft Matter in February 2012. 

Eiscreme im Computertomografen    
Three-dimensional visualization of air bubbles (brown) in ice cream after multiple thaw-freeze cycles as seen in a micro-CT (Fig.: SLF/B. Pinzer).    

Future work by SLF scientists will involve the use of x-ray tomography to study alterations in ice crystal structure during salt treatment of winter roads as well as the metamorphism of ice, water and air mixtures seen in wet snow, a major factor in avalanche formation.

Animations


3-dimensional representation of the air cavities in a small partial volume (2.4 x 2.4 x 0.18 mm³) of ice cream. The images were captured at intervals of 4 hours; the temperature of the ice cream is indicated by the y-axis of the graph at the bottom. Copyright © 2012, Royal Society of Chemistry


This animation shows the same process with ice crystals. Copyright © 2012, Royal Society of Chemistry