An alternative way of shaping chocolate - everyone's favourite food - has been discovered.

Malcolm Mackley, professor of chemical engineering, and his PhD student Yu Wen Chen of Cambridge University have described the use of 'cold extrusion' for moulding chocolate. Solid chocolate is pressed in a die to create flexible straws, in a process which is routine for polymers, pasta and ice cream.

Most chocolate goodies are made by melting and casting methods, but Mackley's technique works at room temperature - below chocolate's melt-in-the-mouth temperature of around 40 °C.  

The straws of chocolate are flexible for a limited period of time, but long enough to be shaped. They can even be tied into knots or coiled like a spring.

Chocolate is a complex semi-solid consisting of sugar crystals and milk and cocoa solids in a matrix of fat, some of it liquid. Mackley and Chen said that some of this liquid fat moves to the walls of the die, easing the chocolate's flow in the extrusion process.

However, 'the structure of chocolate on both the micro- and nanoscale is still not fully experimentally characterised', they said.

Neil D Withers