Copyright © 2021 Food Research Lab. All rights reserved 1

How to Choose Your Next Extruder

Dr. Nancy Agnes, Head,

Technical Operations, FoodResearchLab

info@foodresearchlab.com

In-Brief

During the extrusion process, raw

materials are ground to the preferred size,

which then passes through a

preconditioner. At this stage, steam may

be injected into the raw materials and

finally reaches the die assembly at a

defined throughput. Extruder feeds both

solid and liquid ingredients, mostly grain

pulse, root-based foods, water, oil,

sweeteners, colours, and added vitamins

and minerals.

Extruder’s design and specification can

be tailored for the ideal and intended

manufacturing application of food

products. There is a complex interaction

between feed ingredients, extruder design

and operating conditions, affecting

product development, quality

improvement, consistency, and optimum

operation efficiency.

Extruders can generally be classified

based on the build type, such as single

screw extruder, twin screw extruder,

parallel twin screw extruder, pelletizing

Extruder and dry Extruder. The

following variables affect the efficiency of

the extrusion process. Firstly, raw

material’s physical and chemical

properties, such as viscosity, moisture

content etc. The dough's rheological

behaviour can greatly influence the final

product quality, process time, and heat

transfer. Secondly, thermomechanical

cooking factors, such as the design of the

equipment including the type of screw,

variable screw diameters (D) and lengths

(L) and barrel section of the machine, die

design and opening shape and section.

The die plate assembly design is a crucial

part of the operation as it is responsible

for forming the desired product shape

and adds flow resistance to achieve a

final output of transformed materials.

Bronze dies produce better quality pasta

compared to stainless steel dies. Finally,

operating conditions of the equipment

such as screw speed, temperature and

overall water content contribute to the

process's efficiency.

For instance, during the extrusion

process, caution must be given to the heat

generated from screw elements, the

heating system and the self-heat gained

by the barrel's viscosity. Water is greatly

used in combination with the extrusion

process to characterize the melting

behaviour and overall final dough

Copyright © 2021 Food Research Lab. All rights reserved 2

rheology. Moreover, it is also used in the

form of steam to impact the total extruder

energy output. Such usage can

significantly impact the extruder

selection, design and performance and

mainly on the product quality. The

remaining water is evaporated during the

venting stage to achieve accelerated

cooling to form the final product (3).

There are different categories of

extruders, such as cold, hot, steam-

induced and co-extrusion. Cold extrusion

is mainly used for gentle mixing and

shapes the dough without heating or

cooking, such as pasta. Hot extrusion

converts the raw materials under high

temperature and pressure in a short time.

This type is considered for textured foods

such as pet food. Steam-induced

extrusion is used for determining the

textural attributes of highly expanded

products, such as expanded breakfast

cereals. Co-extrusion can be very helpful

for products with dual textures, such as

crispy shell and soft filling. Co-extrusion

combines stem induced expansion as well

as injection filling.

I. INTRODUCTION

Extruders can be thought of as high

temperature short time cooking (HTST)

equipment, that can transform various raw

ingredients by forcing through a die to

create the desired final product shape

during new product development in the

food development companies. A food

extruder accelerates the restructuring

process for food ingredients, compared to

other traditional food processing methods.

Extruders are highly multi purposed as

they can be used to cook, form, mix, and

texturize food products with added flavour,

quality retention and increased

productivity at a low-cost.

III. GLOBAL LEADERS

There are several types of extruders

available in the market, confusion for food

manufacturers, based on the product type.

Some manufacturers who supply single-

screw extruders are American Extrusion

International, Wenger, Extru-Tech, and

Schaaf Technologie. Companies such as

Buhler, Baker Perkins, Clextral and

Coperion offer twin-screw extruders.

Brabender CW offers extruders at

a pilot scale level. Extruder KE 19 is a

single screw extruder with a screw

diameter of 19mm and has an output of

5kg/hr. Single screw extruders are open

channel extruders, which can be thought of

as a drag flow pump, with the final output

delivery controlled by the pressure flow.

This Extruder comes in handy for product

development, specifically to test the

extrusion properties of different raw

materials and develop the processing

characteristics. Process stimulation could

be done with ease under low R&D costs.

Stimulations such as cold forming,

shaping, gelatinization, plasticization and

expansion. This Extruder also aids in

increasing the time efficiency to

characterize the sensory and rheological

characteristics.

Brabender CW also offer a twin

screw variety, TwinLab-F 20/40. Twin

screw extruders contain two screw as the

name suggests which counter-rotate

forming closed channels. The output from

this type of Extruder is less vulnerable to

pressure flow and can be considered as a

positive displacement pump (2). The

TwinLab-F20/40 model has been designed

for lab scale applications at different L/D

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ratios. New product developments in

snack, breakfast cereals, sweets, and pet

food category can be prepared on a lab

scale. It contains either a 600 or 1200 rpm

motor and horizontally divided barrel that

can be opened to observe and clean. It also

contains 4 different heating zones and

water cooling.

Alternatively, Buhler group offer twin

screw extruders. ECOtwin variety is

specifically tailored for the pet and sea

food industry. It offers a screw diameter of

5 to 7 inches and produces 20,000kg/hr.

Whereas the POLYtwin option is a parallel

twin screw extruder. Its screw diameter

ranges from 2 to 7 inches and offers up to

450 kg/hr. Due to its modular design, it is

highly flexible. It can be used for food

ingredients, breakfast cereals, sea food and

pet food. POLYtwin also offers a robust

and fully automated screw ejection unit,

thus reducing the risk of damaging the

elements. Knife heads can be changed

easily without disrupting the production

process. Flexible cutter for a consistently

high quality end product is yet another

advantage.

REFERENCES

1. Riaz, Mian. (2000). Extruders in food applications.

2. Yacu, W. (2020). Extruder screw, barrel, and die

assembly: General design principles and operation.

Extrusion Cooking: Cereal Grains Processing, 73.

3. Kokini, J. L. (1993). The effect of processing history

on chemical changes in single-and twin-screw extruders.

Trends in Food Science & Technology, 4(10), 324-329.