Applied Physics PhD student: currently studying biofilms in Prof. Michael Brenner's group. This class is changing the way he sees the world. On his morning runs he thinks about the viscoelastic properties of his Saucony shoes. At a cafe, he contemplates the physical properties of the artful foam on his latte. When he cooks dinner, he wonders if this class could lead to some consulting jobs for the food industry.
The Soft Matter Aspects of Making Chocolate
Chocolate is an ideal system for the study of soft matter, since there is a clear correspondence between its physical properties and the experience of consuming it.
- Rheology: The satisfying snap of a high-quality bar of chocolate is the result of a careful balance of particle size distribution, lipid composition, and tempering. The high viscosity of molten chocolate can result in a pasty sensation that persists in your mouth.
- Emulsions: chocolate is an emulsion of sugar and cacao particles in a continuous lipid phase. When chocolate melts in your mouth, it undergoes a phase transition to become an emulsion with a continuous aqueous phase.
- Thin films: to produce the proper particle size distribution, molten chocolate is passed through a system of rollers and is drawn along their surface as a thin film. The shearing action of the rollers breaks up large particles and aggregates.
- Phase transitions: chocolatiers have spent decades perfecting the craft of tempering, to produce a chocolate bar with the ideal physical properties. By switching between higher and lower temperatures, the chocolate makers can produce uniform lipid crystals with the correct form. Without tempering, the chocolate is soft and difficult to remove from molds.
For more information, see: E. O. Afoakwa, A. Paterson, and M. Folwer. "Factors influencing rheological and textural qualities in chocolate - a review." Trends in Food Science & Technology. 18 (2007) 290-298.