| What is the process for manufacturing expanded extruded snacks | Raw ingredient -> Extrusion -> Die cut -> Drying -> Oil & Flavouring -> Packaging |
| How does the extrusion process work | Raw material -> add water -> heat mixture -> hydrate, shear and cook -> pushed out at high pressure -> steam expands product -> product becomes glass -> extrudate is then cut with rotating blade |
| What outputs can change between different extruded snacks (outputs of the factorial design experiment) | Product size, bulk density, texture hardness or water content |
| What parameters can be controlled for an extruder | Screw (speed, shape and dimensions), temperature, screw fill (more full means a higher shear and higher starch damage) and water & ingredients |
| What are the three input factors in the factorial design experiment for extruded snakcs? | Barrel temperature, %water content and screw speed |
| What are the three different screw configurations | Single, twin (tangential) and twin (intermeshing). Single screw is normally cheaper |
| Define specific mechanical energy (SME) | How much energy we put into the extruder |
| How does specific mechanical energy vary with water content | Decreases linearly with time |
| What are the four types of parameters that can be changed in an extruder | Process, system, structure (reactions of different ingredients i.e. gelatinisation of starch etc) and product |
| What can be used instead of steam in the process and why is it better | Carbon dioxide, and used at lower temperature giving different textures |
| What is the main processing differences between pellet extruded snacks and direct extruded snacks | Usually lower temperatures and pressure forming a sheet to be cut and dried. Shear also tends to be lower |
| What is the process for manufacturing pellet extruded snacks | Raw ingredient -> extrusion -> shear and cut -> drying -> frying -> flavouring -> packing
After drying, normally takes place at another location |
| What is the manufacturing process for potato starch | Potatoes from farm -> dry cleaning -> rotary wet cleaning -> mechanical rasping -> centrifuge sieve -> fibre sieve -> hydro cyclones -> vacuum dryer -> flash dryer -> packaging.
CONDENSED PROCESS: clean -> break up -> remove cell debris -> remove water |
| What are the two main components of starch | amylose and amylopectin |
| What is the process for gelatinisation of starch | Raw starch -> heating -> swelling -> rupturing -> gelatinisation/pasting -> imploding |
| Define pasting | Second stage swelling occurs when starch is heated above gelatinisation temperature to obtain max viscosity. More amylose is leached out and eventually gels |
| Define glass | Hard and relatively brittle |
| Draw how a direct extrusion and pellet extrusion snack acts on the diagram below: | See image |
| What are steps 1-6 for direct and pellet extrusion | DIRECT:
1) raw ingredient
2) mix with water and heat
3) glass -> rubber then gelatinisation and melting
4) exit extruder and water nucleation
5) rapid expansion and boil off water
6) dry product
PELLET:
1) raw ingredient
2) extrusion heating and gelatinisation
3) drying pellet becoming glassy
4) heating and expansion
5) pellet leaves fryer and cools down
6) solid glass brittle structure |
| What are some imaging techniques for potato starch | Scanning electron microscope (SEM), x-ray tomography and stained microscopy. Smaller cell walls = harder product |
