Extrusion processing is a modern cooking technique that uses heat, pressure, shear and friction to produce food products. Raw materials are fed into an extruder barrel containing a screw. As the materials are conveyed down the barrel by the rotating screw, heating and pressure increase viscosity into a semi-solid mass. The plasticized material is then forced through a die to produce the final product shape before cooling. Extrusion cooking offers advantages like lower processing costs, less space requirements, and high production rates. However, it also has disadvantages such as larger minimum lot sizes and higher initial costs.

1. Extrusion Processing
Dept. Of Processing And Food Engineering
Presented by :
Potdar Pratik Pandit

2. CONTENTS
1. Introduction and History
2. Principle
3. Factors Affecting Extrusion Cooking
4. Effect of processing variables on protein digestibility
5. Applications In Food Processing
6. Advantages & Disadvantages

3. What is Extrusion Cooking
• Modern (HTST) cooking process(
thermomechanical process) in which heat
transfer, mass transfer, pressure changes
and shear are combined to produce effects
• The food material is heated either by
external heat source or by heat produced
through dies
• Extruder is used to produce extrudate of
different shapes by forcing a specially
designed opening after a previous heating of
the material.
CookingTexturizing
Drying
Enrobing
Cooling
Puffing
Plasticizing
Mixing

4. • The main method of preservation of both hot and
cold extruded foods is by the low water activity of
product
Examples of extruded foods

5. WHY :
 Properly designed convenience foods can make an
important contribution to nutrition
 Social changes are altering traditional patterns of food
preparation

6. HISTORY

8. WORKING PRINCIPLE
• The raw materials are allowed into the extruder barrel and the screw(s) then convey the food
along it
• Further down the barrel, smaller flights restrict the volume and increase the resistance to
movement of the food

9. • As a result, it fills the barrel and the spaces between the screw flights and becomes compressed
• As it moves further along the barrel, the screw kneads the material into a semi-solid, plasticized
mass

10. • Here, frictional heat and any additional heating that is used cause the temperature to rise rapidly
• High temperature of operation in presence of water promotes gelatinization of starch components
and stretching of expandable components

11. • The food is then passed to the section of the barrel having the smallest flights, where pressure and
shearing is further increased
• Finally, it is forced through one or more restricted openings (dies) at the discharge end of the barrel
as the food emerges under pressure from the die, it expands to the final shape and cools rapidly
as moisture is flashed off as steam

12. CUTTING PRINCIPLE
• Must permit obtaining final products with
uniform size
• Product size is determined by the rotation
speed of the cutting blades
• Mechanism can be horizontal or vertical

13. 1) DRAG FLOW :- Flow of material inside the barrel due to the action of dragging
QD = 0.5 π D N Cos Φ (Wh1)FD
2) PRESSURE FLOW :- Reverse flow of the material in the screw channel
QP =
2 𝑊 𝑆𝑖𝑛Φ ℎ2−ℎ1 Δ 𝑃
12 𝐿
1
ℎ1
2−
1
ℎ2
2 μ
FP
Where, W =Width of screw channel, ΔP = pressure drop
h1 & h2 = Depths at the metering and feeding zone, respectively,
D = Barrel diameter, Φ = Helix angle,
N = screw rotation, μ = viscosity of material, and
FD & FP = drag & pressure flow correction factors, respectively.
Material flow in the barrel

14. 3) LEAKAGE FLOW :- Flow through the barrel clearance
GL =
π 𝐷ߜ3 Δ 𝑃
12
𝐿
𝑝
(e/CosΦ) μ𝒔
Where
δ = clearance between screw flight and barrel
ΔP = pressure drop
P = pitch of the screw, and
μ 𝒔 = viscosity of material flowing through channel
Φ = Helix angle
Net flow = Drag flow – Pressure flow – Leakage flow
QNET= QD- QP- QL

15. 1) Extrusion Drive:
 Power supply in food extruder is done by Electric
motors
 The size depends on the capacity of the extruder and
may be as large as 300 KW
 The speed on food extruders is normally less than 500
rpm
 The screw speed on extruder is a valuable control
parameter
EXTRUDER PARTS & COMPONENTS

16. 2) Feeder:
 A device providing a uniform delivery of food ingredients which
are often sticky, non free-flowing substances
 It will regulate rate/pressure of flow. Some types of feeders
commonly used are vibratory feeders, variable speed auger and
weigh belts

17. 3) Barrel or sleeves :
 The barrel is divided into feeding, kneading
 They are often jacketed to permit circulating of
steam or superheated oil for heating and water
or air for cooling

18. 4) SCREW :
 Most important component
 Conveys the materials
 Diameter varies between 2-15 cm Length to
diameter ratio varies between 8-20 and helix
angle between 200 – 30o

19. 5) Die or nozzle:
 Gives shape to the final product and promote
resistance
 Increases internal pressure
 Designed to be highly restrictive, giving
increased barrel fill, residence time and energy
input

20. Extruders
On
Operation
Hot
Extruders
Cold
Extruders
On
Construction
Single Screw Twin Screw
Counter
Rotating
Co-Rotating

22. Operating data for different types of extruders

23. Ingredients
Starch
Water
Protein
Fibre
Lipids
Additives
Provides underlying structure
Complete gelatinization 120°C & 30% MC
Starch
gelatinization
and ingredient
dispersion
Form a continuous
structure Quality of the
product
 Act as a lubricant
 < 5-6 %
 Chemically unchanged
 Influences the expansion of the product
Flavoring & coloring
agents

24. • Structure forming
• Fillers
• Raising
• Plasticizing
Type of feed
materials
• 25 to 30%
• Affects die pressure
Moisture
content
• Cooking
zone 80-150° C
• Higher degree of
gelatinization
Temperatue
• Decides
residence time
• Extrudate
Characterstics
Screw speed
• Die material
Die
Characteristics
• Single screw
• Twin screw
Screw
design
Factors Affecting Extrusion Cooking

25. Effects On Quality of Extruded Products
Nutritional
Properties
Protein
Sugar
StarchDietary
Fibre
Lipids
Digestibility
Sugar losses as sucrose
--- glucose (reducing
sugars) undergo Millard
reaction with proteins
 Subjected to
relatively high
pressure
up to 103 psi
 Gel formation and
viscosity
Insignificant changes in
dietary fibre content
 Lipid is released from
cells
 Torque is decreased ---
lipid reduces slip within
the barrel

26. Effect of processing variables on protein digestibility

27. Functional
Properties
Expansion
Ratio
Bulk
Density
WAI
WSI
Hardness
Effect of the process
parameters was opposite
of expansion ratio
Most dependent on screw
speed and temperature
 Increases with increased
Temp.
 Decreases with increased
MC
 HigherWSI with higher
screw speed
 Increases with increase in
Temp.
 Inverse relationship with
extrudate expansion

28. Influence of process parameters on product expansion

29. APPLICATIONS
• Without Cooking/Distortion
• Ex:- Pasta(/gluten free), Hot Dogs,
Pastry dough, sweet potato extrudates
Cold extrusion
Breakfast/Cereal products
• cornflakes manufacture
• Nutri dal, Fortified rice(/noodles)
Confectionery products • Ex:- Fruit gums, toffee, creams,
Puffed products

30. 2) Low processing Cost
Can save 19 per cent raw material,14 per
cent labor and 44 per cent capital
investment
Eliminates water treatment costs
1) Less space
Needs less space per unit of operation than
other cooking system.
Advantages of extrusion
3) Energy efficient
Operate at relatively low moisture while
cooking food products, so less re-drying is
required

31. 4) Adaptablity
Remarkably adaptable in being able to
accommodate the demand by consumer for
new product
5) High production rates
 production rates of up to 315 kg/h for
snackfoods, 1200 kg/h for low-density cereals
and 9000 kg/h for dry expanded petfoods are
possible (Mans, 1982)
6) Automated production
Can operate continuously and have high
throughputs

32. 7) Product quality
 Involves high temperatures applied for a short
time and the limited heat treatment retains
many heat sensitive components
8) No process effluents
Low-moisture process that does not produce
process effluents
 Does not create problems of environmental pollution

33. Disdvantages
• Larger lot size required as tooling cost is high
• Variations in size/shape of final products possible
• High Initial cost
• May produce carcinogenic acrylamide

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