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level: Snack Extrusion

Questions and Answers List

level questions: Snack Extrusion

QuestionAnswer
What is the process for manufacturing expanded extruded snacksRaw ingredient -> Extrusion -> Die cut -> Drying -> Oil & Flavouring -> Packaging
How does the extrusion process workRaw 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 extruderScrew (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 configurationsSingle, 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 contentDecreases linearly with time
What are the four types of parameters that can be changed in an extruderProcess, 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 betterCarbon dioxide, and used at lower temperature giving different textures
What is the main processing differences between pellet extruded snacks and direct extruded snacksUsually 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 snacksRaw ingredient -> extrusion -> shear and cut -> drying -> frying -> flavouring -> packing After drying, normally takes place at another location
What is the manufacturing process for potato starchPotatoes 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 starchamylose and amylopectin
What is the process for gelatinisation of starchRaw starch -> heating -> swelling -> rupturing -> gelatinisation/pasting -> imploding
Define pastingSecond stage swelling occurs when starch is heated above gelatinisation temperature to obtain max viscosity. More amylose is leached out and eventually gels
Define glassHard 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 extrusionDIRECT: 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 starchScanning electron microscope (SEM), x-ray tomography and stained microscopy. Smaller cell walls = harder product