Watch the extrusion process for making crispy snacks from taewa (Māori potatoes). These prototype snacks are being made at a pilot plant at the Riddet Institute in Palmerston North.
A mixture of taewa flour and corn flour is poured into the hopper of the extrusion machine.
Water is added to this mixture before it enters the extruder barrel.
The wet mixture is heated and kneaded by two rotating screws inside the extruder barrel.
This action causes starch granules in the flour to swell and rupture.
An homogenous dough is formed as the screws move the mixture forward through a series of heating and shearing zones.
The dough is cooked further before it enters the final high-pressure zone.
Pressure forces the dough through a small opening in a die at the end of the extruder barrel. As it exits the barrel the sudden decrease in pressure causes the dough to expand rapidly as water evaporates off.
The expanded material is cut into small bite-sized snacks. The shape of the die opening controls the shape of the snacks.
The expanded snacks then enter a dryer that reduces and stabilises the moisture content. Flavouring and colouring may be added before the snacks are packaged.