Food extrusion

1. FOOD PROCESSING
Extrusion Technology
In of Food Processing
Er. Shelke G.N
Assistant Professor
Department of Food Engineering
CFT Ashti,
Maharashtra 414202
Phone: +919561777282
E-mail: shelkeganesh838@gmail.com

2. Point to be covered
 Introduction.
 Advantages of Extrusion
 Advantages of Extrusion
 Popularity of Extrusion Cooking
 Principle of Extrusion Cooking
 Classification of Extruders
 Factors Affecting Extrusion Cooking

3. Extrusion cooking is a modern (HTST) cooking process
(thermo-mechanical process) in which heat transfer,
mass transfer, pressure changes and shear are combined
to produce effects such as,
 Cooking,
 Sterilization,
 Drying,
 Melting,
 Cooling,
 Texturizing,
 Conveying,
 Puffing,
 Mixing,
 Kneading,
 Forming, etc.
It is important food process in the manufacture of pasta,
ready‐to‐eat cereals, snacks, pet foods
Introduction

4.  Extrusion-technology is gaining increasing popularity
in the global agro-food processing
 Extrusion cooking technologies are used for cereal
and protein processing in food.
 Now a day’s consumers do choice for nutritionally rich,
therapeutic benefits and for attractiveness especially in
case of baby foods.
 Thus to obtain above mentioned designer food, Food
Extrusion technology is used.
Introduction

5.  Extrusion cooking is a high-temperature
short-time (HTST) process.
 which reduces microbial contamination and
inactivates enzymes.
 The main method of preservation of both
hot- and cold-extruded foods is by the low
water activity of the product (0.1–0.4),
and for semi-moist products in particular,
by the packaging materials that are used.
Introduction

6.  Extrusion brings gelatinization of starch,
denaturation of proteins,
 Modification of lipids inactivation of enzymes
and many anti nutritional factors,
 It reduces microbial contamination,
and inactivates enzymes.
Introduction

7. Advantages of extrusion
 Adaptability:
The extrusion process is remarkably
adaptable in being able to accommodate
the demand by consumers for new product

8.  Product characteristics:
A variety of shapes, texture, color
and appearances can be produced,
which is not easily formed using
other production methods

9.  Energy efficient:
Extruders operate at relatively
low moisture while cooking
food products, so less re-drying is
required

10.  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.  Less space:
extrusion processing needs less space per unit of operation than
other cooking system

12. Popularity of Extrusion Cooking
 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

13. Popularity of Extrusion Cooking……
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,
reducing water treatment costs and levels of
environmental pollution

14. History Of The Extruder

15. Principle of Extrusion Cooking
 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.

16. Principle of Extrusion Cooking ……
 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).

17. Principle of Extrusion Cooking …
 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.

18. Principle of Extrusion Cooking ……
 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.

19. Examples for Extrusion Foods
 Pasta
Ready-to-eat (RTE) cereals
Puffed cereals, shredded cereals, etc.
 Snack products
Corn curls, puffed snacks, crisp breads,
co extruded products, etc.
 Pet foods
Dry, semi moist
 Confectionery products
Licorice, toffee, caramel, peanut brittle
 Texturized proteins
Meat analogs, fish paste (surimi)

21. The basic elements of proper extrusion cooking are the following:
1) Feeding of granular or milled material in
the extruder should be continuous at desired
feed rates.
2) The material should be pre-conditioned with
steam at controlled temperature of 800
C to
800C at atmospheric pressure.
3) The moisture should be uniformly applied
to the product.
4) The equipment must transform the granular
or processed floury material into a dough at
820
C to 1100
C

22. 5) The temperature of the dough should be
elevated to 1150
C to 2000
C during last
10 to 30 seconds in their extruder to cook
and expand the product.
6) Formation of desired shape and size of the
product by a nozzle or die at the end of the
process the extrudate is cut into desired
lengths.
7) Drying and cooling of the extrudate.

23. Classification of Extruders

24.  Hot Extrusion:
If the food is heated above 100ºC the
process is known as extrusion cooking.
 Cold Extruders:
If the food is heated below 100ºC the
process is known as cold extrusion.
 The main method of preservation of
both hot- and cold-extruded foods is
by the low water activity of the product
(0.1–0.4)

25. Cold extrusion
 In this process, the product is extruded without
cooking or distortion of the food.
 The extruder has a deep-flighted screw, which
operates at a low speed in a smooth barrel, to
knead and extrude the material with little friction.
 It is used to produce pasta, hot dogs, pastry
Dough and some types of confectionery.
 Typical operating conditions are shown
in Table 14.2 for low shear conditions.

26. Hot Extrusion cooking
 High pressures and temperatures are used to
form expanded products.
 The rapid release of pressure as the food
emerges from the die causes instantaneous
expansion of steam and gas in the material,
to form a low-density product.
 Hot extrusion is a HTST process, which
minimizes the loss of nutrients and reduces
microbial contamination.
 The moisture content of some products,
for example snack foods, crispbread and
breakfast cereals, is further reduced after
extrusion by drying.

27. Single-screw extruders
 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

30. Feed section
 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.

31. Compression section
 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;

32. Metering section
 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;

33.  The raw materials are fed in a granular form at
the hopper located in the feed section.
 The rotating action of the screw conveys the
material to the transition section.
 In the transition section, the screw channel
becomes shallower and the material is
compacted.
 A major portion of mechanical energy is
dissipated in this section, which results in a rise
in temperature of the material.
 Starch becomes gelatinized, and the material
becomes more cohesive.

34.  It is transported further by the metering section
and pushed through the die opening.
 The barrels of single-screw extruders usually
have helical or axial grooves on the inner
surfaces.
 This helps to convey and mix the material more
effectively.
 Single-screw extruders are usually characterized
by their length to diameter (L/D) ratio and their
compression ratio.
 The throughput (mass flow rate) capacity of a
single-screw extruder is linked to screw speed,
screw geometries, and material characteristics.

35. Extruder Parts & Components
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.

36. 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.

37. 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.

39. 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 20o – 30o .

47. 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.

48. 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

51. Twin-screw extruders
 The term ‘twin-screw’ applies to extruder s
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.

55. Twin-screw extruders are mainly of
two types as follows.
Counter- rotating twin- screw extruder
1) Non-intermeshed, counter rotating
2) Intermeshed, counter rotating
Co-rotating twin-screw extruders
1) Non-intermeshed, co-rotating
2) Intermeshed, co-rotating

56. 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

57. Characteristics of Extruded Products
 Degree of Expansion on Exit from the Extruder.
 For many products, the sudden release of pressure
when exiting the die of the extruder causes water
to flash off and the product to expand.
 The extent of expansion depends on the composition
of the product, its internal microstructure as it exits the
die, and the conditions (pressure and temperature) in
the extruder.
 Degree of expansion may be calculated as either the
ratio of the diameters or areas of the extruded
product to the die

58.  Bulk Density.
The density of the final product depends on the
nature of the solid material as well as on the
amount of air space within the product.
A highly expanded product, with plenty of air
spaces, has significantly lower bulk density
than a product with little air inclusion.

59.  Mechanical Properties.
 Physical and rheological properties determine the
characteristics of the extruded product.
 These may be expressed as fundamental parameters,
like elastic modulus, or may be characterized by
Empirical measures, such as hardness or crispness.
 Instruments that measure fundamental properties
(rheometers) or empirical techniques (Instron or
penetrometer) may be used to quantify characteristics
of extruded products.

60.  Internal Microstructure.
 The arrangement of the components of the extruded
product leads to the physical properties described above.
 The state of starch, whether partially or completely
gelatinized, in the final product strongly influences
physical characteristics.
 Typically, internal microstructure is evaluated using
microscopy (scanning electron microscopy).

61.  Protein Quality.
 The nature of extruded proteins depends on the Extruder
operating conditions, especially temperature profile as the
extruded product is formed.
 High-heat treatment causes denaturation of many proteins,
which influences physical characteristics such as viscosity.

62.  Starch Characteristics.
 Properties of starch in an extruded product that
influence quality characteristics include such
measures as water absorption index, water
solubility index, and enzyme susceptibility.
 These depend on the operating parameters
within the extruder as well as the type of
raw materials used for extrusion.

63. Factors Affecting Extrusion Cooking
Rheological properties of the food
The properties of the feed material have an important
influence on the texture and color of the product;
the most important factors are:
1) The type of feed materials
2) Their moisture content
3) The physical state of the materials
4) Their chemical composition, particularly
the amounts and types of starches, proteins,
fats and sugars
5) The pH of the moistened material.
6) Feed rate
7) Screw speed
8) Barrel temperature
9) Die characteristics
10) Screw design

64. Operating characteristics
The most important operating parameters in an extruder are
1) Temperature
Increase in extrusion temperature results in
higher degree of gelatinization.
2) Pressure
3) Diameter of the die apertures
Increase in diameter reduces gelatinization of starch
4) Shear rate
5) Moisture
If moisture increases viscosity decrease torque
decrease product temperature decrease bulk
density increase (expansions die pressure decreases).