Check out Jordan Miller’s open hardware Baricuda Extruder for 3D Printing Sugar and Chocolate shared on Thingiverse:

Introducing the Baricuda Extruder for 3D Printing Sugar and Chocolate

Derived from the venerable MakerBot MK2 Frostruder, this air-pressure driven extruder (“baric”) is a *U*niversal extruder because it adds a *D*egree *A*mplifier (yep… temperature) to let you extrude anything.

The Source Code and Files are Hosted on Github: github.com/jmil/BariCUDA

We used this to precisely extruder sugar templates for engineering vascular tissues for regenerative medicine research. See the details here:
youtube.com/watch?v=9VHFlwJQIkE

You can use it for:

1. Molten Sugar Extrusion
2. Molten Chocolate Extrusion
3. Molten PLA and ABS and other experimental plastics Extrusion
4. Molten Extrusion — This is a *U*niversal Extruder! Any thermoplastic material can be extruded.

You are only limited by your motherboard and the number of MOSFETs you have (for control of pneumatics just like the Frostruder).

Operation is IDENTICAL to the Frostruder, you just need to add a heating element and thermistor for temperature measurement.

Read more.