Extrusion cooking is a thermomechanical process that uses an extruder to apply heat, pressure, shear and mixing to ingredients. An extruder consists of a barrel, screw, die and other components. As ingredients are conveyed through by the screw, compression increases pressure and temperature, cooking and shaping the material before it exits through the die. Extruders can be single or twin screw, and are used for processes like drying, puffing, and texturizing of foods like snacks, cereals and pet foods. Extrusion cooking offers benefits like versatility, reduced costs, high production rates and product quality with no process effluents.

1. EXTRUSION COOKING
Shubham Nimbkar
I PhD FPE

2. INTRODUCTION
• Extrusion: (Latin word extrudere): Action of pushing out
• Forcing material out of narrow gap
• Extrusion Cooking: Thermomechanical process
• Heat transfer, mass transfer, pressure changes and shear
• Cooking, sterilization, drying, melting, cooling, texturizing, conveying, puffing, mixing,
kneading, forming, etc.
• Extrusion cooker is a combination of a pump, a heat exchanger, a continuous high-
pressure-high-temperature reactor

3. BASIC STRUCTURE OF SINGLE SCREW
EXTRUDER

4. COMPONENTS
• Barrel: Hollow cylindrical enclosure. Encloses screw
• Screw/worm: A helical part that conveys, works and forces the ingredients through the
die
• Die: Small opening at the end of the extruder to shape the products
• Breaker plate: A mechanical seal between die and end of extruder
• Jacket: For heating or cooling of barrel
• Hopper: For feeding of ingredients

5. Extrusion drive
• Function: rotation of screw
• Electric motor
• Size depends on capacity of extruder (can be as large as 300 kW)
• Screw speed: usually less than 500 rpm
Feeder:
• Uniform delivery of food ingredients to the extruder
• Regulates the pressure and flow of feed
• Auger feeder, hopper, vibratory feeder.

6. BARREL
• Hollow and cylindrical (in food industry)
• The internal surface can be smooth or grooved
Single screw barrel Twin screw barrel

7. SCREW
• Most important component
• Conveys, shears and plasticizes the mass
• Diameter of a screw of a single screw extruder normally varied between 2-15 cm

8. SOME IMPORTANT TERMS
Flight: A helical conveying surface of screw, which pushes raw material further
Flow channel: a helicoidal channel between screw root and barrel
Pitch: Distance between two consecutive flights
L/D ratio: Ratio of length to diameter of screw
Compression ratio: Ratio of volume of full flight at start and end of the extruder

10. DIE
• Two main functions: Give shape and promote resistance
• Increases internal pressure
• Various designs and number of orifices
• Designed to be highly restrictive, giving increased barrel fill, residence time and energy
input

11. OPERATION
• The raw material is fed to the barrel which is conveyed further by screw
• The screw configuration is such a way that the flow channel area is progressively
reduced causing compression of the fed material.
• As it moves forward, the screw kneads the material into a semi-solid, plasticized mass

12. SECTIONS OF EXTRUDER
• Feed Section: Acts as screw conveyor. No compression or modification occurs. Deep
flights so that feed falls easily between them.
• Compression Section: Food ingredients are compressed, sheared and heated.
Material is worked into viscous dough, partially cooked at elevated temperature and
pressure.
• Metering Section: Nearest to discharge. Very shallow flights leads to increased shear
and mixing causing melting, texturization, kneading, chemical reactions, etc.

13. • Heating: through friction, heated barrel surface, direct steam injection
• Due to higher pressure, higher temperature (180-200˚C) is achieved.
• The pressure is suddenly released at the exit from the die, some water is flash
evaporated and product is puffed.
• Two flows:
• Drag flow
• Pressure driven backflow

14. Temperature and pressure profile

15. CLASSIFICATION OF EXTRUDERS
Based on
operation
Hot extruders
(>100˚C)
Cold
extruders
(<100˚C)
Based on
construction
Single screw Twin screw
Co-rotating
Counter-
rotating

16. DRY EXTRUDERS
• Does not require external source of heat or steam or jacket
heating
• Heating is accomplished only through friction
• Wide range of moisture: 10-40%
• Preconditioning with steam or water is necessary
• Temperature: 82-160˚C
• Applications:
• preparing oilseeds for screw pressing of oil
• Cereals and starches
• TVP
• Stabilization of rice bran
• Pet food

17. INTERRUPTED FLIGHT EXTRUDER
• Also called as ‘expanders’
• Shaft with interrupted flights inside a smooth
barrel
• Removable stationary pins protruding from barrel
and intermeshing with interruptions
• Provides high shear, turbulent mixing action
which provides rapid and uniform absorption of
moisture.
• Temperature: 120-150˚C
• Applications:
• Processing of pet foods
• Preparing of oilseeds for solvent extraction
• Aquaculture feed

18. TWIN SCREW EXTRUDER
• A pair of parallel screws rotating inside a barrel with an 8
shaped cross section
• Rotation: Corotating, counter-rotating
• Position: Intermeshing, non-intermeshing
• Self wiping corotating twin screw extruder is most widely
used
• Applications:
• For processing of sticky products such as caramel, candies
• Cocoa and crumb
• Dairy products
• Instant noodles

19. MAJOR FEATURES
Versatility
Reduced Cost
High production
rate and
automated
production
Product quality
No process
effluents

20. THANK YOU!!!