This document discusses extrusion, an important food processing technique. It defines extrusion as pushing material through an orifice or die using a piston or screw. Extruders contain three main sections - feeding, compression, and metering. They allow for continuous high-temperature short-time processing to cook, shape, and form foods. Extrusion is versatile and can produce a variety of product types from cereals to protein products in a cost-effective manner.

1. Presented to:
Er. Abhinav Kapila
Presented by:
Malvika
M.E (FT) 1st yr
1955
Dr. SS Bhatnagar University Institute of Chemical Engineering and Technology
Panjab University, Chandigarh
160014

2. INTRODUCTION
• The word “extrudate” originates from the Latin word “ex”(out) and
“trudere” (to thrust).
• Extrusion is defined as “A process in which material is pushed through
an orifice or a die of given shape, the pushing force is applied using a
piston or a screw.”
• Extrusion is also known as extrusion cooking which is a high
temperature short time (HTST) process.
• Extruder is the equipment which is used for extrusion.
• Extrudate is the final product that comes out of the extruder.

3. • Six processes involved in the process of extrusion are:
1. mixing
2. kneading
3. cooking
4. shearing
5. shaping
6. forming
Other secondary processes involved are:
conveying, separation, venting, flavor generation, plastification and
expansion of the food structure.

4. INVESTIGATOR YEAR FINDINGS
MC.Anelly
1964 First to describe a process for the
production of spongy elastic
particles from soy flour.
Atkinson
1970 Disclosure of a continuous cooking
extrusion process
EL-Dash 1981
First to process breakfast cereal
products
Noguchi 1998
Extrusion cooking of high moisture
protein foods
Fast 2000 RTE cereals

5. Saalia Ryan 2011
Degradation of afflatoxins by
extrusion
Ryan 2011
Oat based breakfast cereal
snack

6. • Versatility: A wide range of products, many of which cannot be produced
easily by any other process, is possible by changing the ingredients,
extruder operating conditions and dies.
• Cost: Extrusion has lower processing costs and higher productivity than
other cooking and forming processes.
• Productivity: Extruders can operate continuously with high out put.

7. • Product quality: Extrusion cooking involves high temperatures
applied for a short time, retaining many heat sensitive components of a
food.
• Environmentally-friendly: As a low-moisture process, extrusion cooking
does not produce significant process effluents,

8. 1. Extrusion reduces microbial contamination and causes inactivation of
enzymes due to high temperature processing.
2. The main method of preservation of both hot- and cold-extruded foods is
the low water activity of the product (0.1–0.4).
3. For semi-moist products in particular by the use of packaging materials.
4. Extrusion brings
• gelatinization of starch
• denaturation of proteins
• modification of lipids
• inactivation of enzymes and reduces microbial contamination
• reduces many anti nutritional factors

9. • Adaptability: The extrusion process is remarkably adaptable in being able to
accommodate the demand by consumers for new product
• Product characteristics: A variety of shapes, texture, color and appearances can be
produced,
which is not easily formed using other production methods.
• Energy efficient: Extruders operate at relatively low moisture while cooking food
products, so less re-drying is required

10. • Less space: Extrusion processing needs less space per unit of operation
than other cooking system.
• Low cost: extrusion has lower processing costs than other cooking and
forming processes. We can save 19 per cent raw material, 14 per cent
labor and 44 per cent capital investment

11. 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.

12. • 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.
• If the food is heated above 100ºC the process is known as extrusion
cooking (or hot extrusion).

13. • 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.

14. • 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.

15. Types of product Examples
Cereal based products Instant drinks
Weaning foods
Puffed breakfast cereal
Pasta products
Sugar based products Chewing gum
liquorice
Toffee
Caramel
Fruit gums
Protein based products Texturised Vegetable Protein
(TVP)
Semi moist and expended pet
foods, animal feeds
Protein supplements
Sausage products
Surimi
Caseinates
Processed cheese

16. • The output of an extruder varies with the inside diameter (D) of the
barrel.
• Common sizes are 60, 90, 115, and 150 mm (2.5, 3.5, 4, and 6 inches),
with output approximately doubling with each size increment.
• Length (L) of the barrel is measured from the end of the feed throat
section to the die.

17. • Extruder barrels are made from:
• Nitriding steels
• Powder metallurgy steels, or
• Bi-metals which are composed by two separates parts: a support base material and an
internal lining.
Bi-metals are composed of two separate parts; a supporting base matreial and an internal
lining.
• Extruder screws are made from:
• Nitriding steels
• Case-hardening / or nitriding steels
• Core-hardening steels
• Powder metallurgy steels.

18. • Hopper is made from
• Aluminum although stainless steel is preferable. Simple gravity feed is most
often used with a conical hopper, unless the material does not flow
uniformly.
• Gear box: Stainless steel, Cast Iron.
• Nozzles:
• Stainless steel nozzles
• Brass nozzles: It is the most used material for the nozzles of the extruders,
because it has a high thermal conductivity and stability, in addition to its
ease of machining and economic price. Its main drawback is the fast wear to
abrasive materials that contain fibers.

19. • Thermal stress : It is generated when a body in restriction is subjected to
temperature change.
• Heating of the food material by the use of heat exchanger in the extruder
occurs as the food is being cooked thus also called hot extrusion. Cooling of
the food material also occur inside the extruder during cold extrusion.
• This use of temperature causes thermal stress in the extruder.
• Torsional shear stress: A stress developed in the shaft when it is subjected to a
twisting moment or torsion.
• The screw used rotates for mixing, pushing the food material to the die. Its
rotating action creates torsional shear stress in the screw.

20. Dynamic stress: Stresses that are developed in material subjected to
some of kinetic energy like rotatingdisc,rim, turbine etc.
• The rotating movement of screw leads to the development of dynamic
stress.

21. Single Screw Twin Screw
Co- rotating Counter
rotating

22. • These contain a single rotating screw in a metal barrel, and come in varying patterns.
• The most commonly used single-screws have a constant pitch.
• Single-screws usually consist of three sections.
1) Feed
2) Transition or compression
3) Metering

24. • The portion of the screw which accepts the food materials at the feed port.
• Usually the feed section is characterized by deep flights so that the product can easily
fall in to the flights.
• The function of the feed section is to assure sufficient material moved or conveyed
down the screw and the screw is completely filled.

25. • The portion of the screw between the feed section and the metering section is called as
compression section.
• The food ingredients are normally heated and worked into a continuous dough mass during
passage through the transition section.
• The shearing/compression section in which the materials are thoroughly worked into viscous
dough, partially cooked and elevated in temperature and pressure.
• The portion of the section nearest the discharge of the extruder which is normally characterized by
having very shallow flights.
• The shallow flights increase the shear rate in the channel to the maximum level with in the screw.
• The metering section in which dough is further cooked and starch granules may be broken down due
to higher shear forces.
• The metering section continuously feeds the die with materials at uniform pressure

26. Extrusion Drive:
• The Power supply in food extruder is done by Electric motors.
• The size of the motor depends on the capacity of the extruder and may be as large as 300
KW.
• The screw speed on extruder is a valuable control parameter.
• The speed on food extruders is normally less than 500 rpm.
• Thrust bearing must be able to sustain the load produced under normal extrusion
conditions giving an expected life of 20,000 to 50,000 hr.
Feeder:
• A device providing a uniform delivery of food ingredients which are often sticky, non-
free_x0002_flowing substances.
• It will regulate rate/pressure of flow. Some types of feeders commonly used are vibratory
feeders, variable speed auger and weigh belts.

28. Barrel or sleeves
• The barrel is divided into feeding, kneading an the sleeves surrounding the screw
can be solid.
• They are often jacketed to permit circulating of steam or superheated oil for
heating and water or air for cooling.

29. Screw
• The screw of the extruder is certainly its most important component
• The screw which conveys the materials.
• Diameter of the screw of a single screw extruder normally varies between 2-15 cm.
• Length to diameter ratio varies between 8-20 and helix angle between 20︒-30︒

30. Die or nozzle:
• The die presents two main functions: give shape to the final product and promote
resistance.
• It increase in internal pressure.
• The die can present various designs and number of orifices .
• Dies may be designed to be highly restrictive, giving increased barrel fill, residence time
and energy input.
• Die design and its effects on functional properties and quality of a final product.

31. Cutting mechanism
• The cutting mechanism must permit obtaining final products with uniform size.
• Product size is determined by the rotation speed of the cutting blades.
• This mechanism can be horizontal or vertical
• Advantages of Single-screw
extruders
1) It is a short time process
2) No waste products
3) Versatility in application

32. Twin-screw extruders
• The term ‘twin-screw’ applies to extruders with two screws of equal length placed inside
the same barrel.
• It consists of two parallel screws in a barrel.
• It is more complicated than single screw extruders.
• It provides much more flexibility and better control.
• Twin screws produce a more uniform flow of the product through the barrel due to the
positive pumping action of the screw flights.

33. Twin-screw extruders are mainly of two types as follows.
1. Counter- rotating twin- screw extruder
1) Non-intermeshed, counter rotating
2) Intermeshed, counter rotating
2. Co-rotating twin-screw extruders
1) Non-intermeshed, co-rotating
2) Intermeshed, co-rotating
Advantages of Twin Screw Extruders
1) Handle viscous, oily, sticky or very wet material and some other products which will slip in
single screw extruder (it is possible to add up to 25% fat in a twin screw extruder)
2) Less wear in smaller part of the machine than in single screw extruder.
3) Wide range of particle size (from fine powder to grains) may be used whereas single screw
is limited to a specific range of particle size