ICAR AICE-JRF/SRF Extrusion & Texturisation Technology: practice questions

1 · Single-screw extruders: flow and pressure · hard

A screw with D = 0.08 m turns at 2 rev/s with helix angle 17.7°; the channel is 0.06 m wide and 0.006 m deep. Using Qd = ½VzWH with Vz = πDN cos θ, the drag flow is closest to

1. 0.62 m³/h
2. 0.31 m³/h
3. 0.33 m³/h
4. 8.62e-05 m³/h

2 · Single-screw extruders: flow and pressure · medium

Grooved barrels are used in single-screw food extruders to

1. prevent slip at the barrel wall
2. heat the material by radiation
3. separate fat from the melt
4. reduce die pressure

3 · Single-screw extruders: flow and pressure · hard

Using a die with smaller openings on the same extruder generally

1. lowers die pressure and raises output
2. raises die pressure and lowers output
3. has no effect on pressure
4. stops the screw rotating

4 · Twin-screw extruders: configuration and screw elements · medium

Food twin-screw extruders commonly have length-to-diameter ratios of about

1. 2–4
2. 200–400
3. 0.2–0.4
4. 20–40

5 · Starch transformations during extrusion · medium

Vitamins are usually added to extruded cereals

1. after extrusion, by spraying or coating
2. before extrusion, so that they survive the barrel heat
3. only in the die
4. never

6 · Protein texturisation: low-moisture and high-moisture extrusion · hard

A meat analogue needs 45 N to cut perpendicular to its fibres and 15 N parallel to them. Its anisotropy index is

1. 0.33
2. 3.0
3. 30
4. 60

7 · Protein texturisation: low-moisture and high-moisture extrusion · medium

Switching to a different supplier's pea protein changes meat-analogue texture markedly. The best response is to

1. specify protein functionality and re-run extrusion trials
2. ignore the change
3. raise the price
4. stop using a cooling die and expand the product at the die instead

8 · Die design and product shaping · hard

Halving the radius of a circular die opening, other things equal, raises the die pressure drop by a factor of

1. 2
2. 4
3. 16
4. 8

9 · Protein texturisation: low-moisture and high-moisture extrusion · hard

Phase separation between protein-rich and water- or polysaccharide-rich phases in high-moisture extrusion is thought to

1. prevent any fibre formation in the cooling die
2. contribute to the layered, fibrous structure
3. cause expansion at the die
4. convert protein into starch

10 · Pasta and cold-forming extrusion · easy

Dried pasta is dried to a final moisture of about

1. 30 %, the dough moisture before drying
2. 50 %, to keep it soft in the pack
3. 0 %, removing every trace of water
4. 12 %