GATE Extrusion & Texturisation Technology: practice questions

GATE — Life Sciences (XL), Section U Food Technology · India · IITs and IISc on rotation (2026: IIT Guwahati)

Original practice questions written to the published syllabus · not past papers

10worked here, free

38written to this exam in this subject

11syllabus units

What this subject covers

The extruder as a continuous cooker and shaper: single- and twin-screw extruders, the transformations of starch and protein inside them, expanded snacks, breakfast cereals, pasta, and high-moisture extrusion for meat analogues.

In the exams: GATE XE-G Section 3 (extruded products, ready-to-eat breakfast cereals); ICAR AIEEA-PG Code 18 Unit II (extrusion)

Principles of extrusion cooking
Single-screw extruders: flow and pressure
Twin-screw extruders: configuration and screw elements
Die design and product shaping
Specific mechanical energy and process variables
Starch transformations during extrusion
Protein texturisation: low-moisture and high-moisture extrusion
Expanded snacks and ready-to-eat breakfast cereals
Pasta and cold-forming extrusion
Co-extrusion and filled products
Quality evaluation of extrudates: expansion ratio and bulk density

What GATE asks from it

GATE — Engineering Sciences (XE), Section G Food Technology

Section 3 names extruded products and ready-to-eat breakfast cereals under cereal processing. Expect questions on extrusion principles, single- versus twin-screw extruders, effects of moisture and temperature on expansion, starch transformation, and calculations of SME, expansion ratio and bulk density.

GATE — Life Sciences (XL), Section U Food Technology

Same scope as XE-G; questions often link extrusion to starch and protein chemistry (gelatinisation at low moisture, fragmentation, protein texturisation).

Where the 38 questions fall

How our questions for GATE spread across the units of Extrusion & Texturisation Technology. Difficulty: 16 easy, 11 medium, 11 hard.

Principles of extrusion cooking	6
Starch transformations during extrusion	5
Expanded snacks and ready-to-eat breakfast cereals	5
Die design and product shaping	4
Specific mechanical energy and process variables	4
Twin-screw extruders: configuration and screw elements	3
Pasta and cold-forming extrusion	3
Quality evaluation of extrudates: expansion ratio and bulk density	3
Single-screw extruders: flow and pressure	2
Protein texturisation: low-moisture and high-moisture extrusion	2
Co-extrusion and filled products	1

10 practice questions, worked

Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.

1 · Principles of extrusion cooking · easy

Extrusion cooking is best described as a

low-temperature long-time process
freezing process
fermentation process
high-temperature short-time process

Answer and working

D. high-temperature short-time process

Temperatures of roughly 100–180 °C for tens of seconds cook and shape the food.

Further reading: Guy (ed.), Extrusion Cooking: Technologies and Applications

2 · Principles of extrusion cooking · medium

In many cooking extruders, most of the heat comes from

electric heaters mounted inside the hollow screw shaft
microwave sources in the barrel
viscous dissipation of mechanical energy
radiation from the die

Answer and working

C. viscous dissipation of mechanical energy

Friction and shear in the viscous melt convert motor energy into heat; barrel heating supplements it.

Further reading: Guy (ed.), Extrusion Cooking: Technologies and Applications

3 · 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

0.62 m³/h
0.31 m³/h
0.33 m³/h
8.62e-05 m³/h

Answer and working

B. 0.31 m³/h

Vz = π × 0.08 × 2 × cos 17.7° = 0.479 m/s; Qd = ½ × 0.479 × 0.06 × 0.006 = 8.62e-05 m³/s = 0.31 m³/h. Doubling omits the ½; omitting cos θ gives 0.33; the last leaves the value in m³/s.

Further reading: Harper, Extrusion of Foods

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

Net output of a single-screw extruder equals

pressure flow plus drag flow
the die flow multiplied by the screw speed in revolutions per second
drag flow minus pressure flow and leakage
leakage flow only

Answer and working

C. drag flow minus pressure flow and leakage

Back-pressure from the die opposes drag flow; leakage over flights reduces output further.

Further reading: Harper, Extrusion of Foods

5 · Die design and product shaping · medium

An extrudate leaves the die at 2.0 m/s and is cut by a two-blade knife at 600 rpm. The piece length is about

20 cm
5 cm
0.3 cm
10 cm

Answer and working

D. 10 cm

Cuts per second = 600/60 × 2 = 20; length = 2.0/20 = 0.10 m = 10 cm. 20 cm ignores the second blade; 5 and 0.3 are slips.

Further reading: Guy (ed.), Extrusion Cooking: Technologies and Applications

6 · Starch transformations during extrusion · easy

At the low moisture of extrusion, starch granules are transformed mainly by

swelling of granules in excess water, as in a sauce
fermentation by yeasts
freezing and thawing
shear and heat disrupting and melting them

Answer and working

D. shear and heat disrupting and melting them

There is too little water for full swelling; mechanical and thermal energy melt and disperse starch.

Further reading: Guy (ed.), Extrusion Cooking: Technologies and Applications

7 · Starch transformations during extrusion · hard

Waxy (amylopectin-rich) starches in extrusion tend to give

light, highly expanded products
dense, hard products
products that cannot expand
products with no starch conversion

Answer and working

A. light, highly expanded products

Amylopectin-rich melts often expand more; high-amylose starches give denser products.

Further reading: Guy (ed.), Extrusion Cooking: Technologies and Applications

8 · Expanded snacks and ready-to-eat breakfast cereals · easy

Corn curls (collets) are an example of

direct-expanded snacks
third-generation pellets
cold-formed pasta
fried potato slices

Answer and working

A. direct-expanded snacks

They expand at the die and need only drying and seasoning.

Further reading: Guy (ed.), Extrusion Cooking: Technologies and Applications

9 · Expanded snacks and ready-to-eat breakfast cereals · easy

Third-generation snack pellets are expanded

inside the extruder barrel before they reach the die
by freezing
later, by frying, hot air or microwave
by adding yeast

Answer and working

C. later, by frying, hot air or microwave

Dense glassy pellets are dried and puffed in a separate step.

Further reading: Guy (ed.), Extrusion Cooking: Technologies and Applications

10 · Expanded snacks and ready-to-eat breakfast cereals · hard

Snack pellets are dried to about 10–12 % moisture mainly to

expand them fully
make a stable, glassy intermediate
sterilise them by heat
prepare them for freezing

Answer and working

B. make a stable, glassy intermediate

Dense pellets store and ship cheaply; residual water drives later expansion.

Further reading: Guy (ed.), Extrusion Cooking: Technologies and Applications

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