Table of Contents

Food & Feed Extrusion Technology:
An Applied Approach to Extrusion Theory

Preface
1. Overview of the Extrusion Process
1.1 A Brief History of Extrusion
1.2 The Range of Extruded Products
1.3 The Extrusion System
1.4 Basic Features of an Extruder

SECTION 1: INTRODUCTORY CONCEPTS  
2. Principles of Extruder Configurations 
2.1 Basic Types of Extruder
2.2 The Extruder Screw
2.3 The Extruder Barrel
2.4 The Extruder Die
2.5 A Simple Analogy for Extruder Performance

3. Rheology & Flow in Extrusion Processing 
3.1 A Definition for Fluid Viscosity
3.2 Viscoelasticity
3.3 Flow Components in an Extruder Screw

4. The Development of Optimal Screw Profiles
4.1 - Introduction
4.2 - Classification of the Performance Characteristics of alternative Screw Elements
4.3 – Calculation of the Performance Characteristics - Single Screw
4.4 Worked Example – Estimate the Filled Length (Single Screw)
4.5 – Calculation of the Performance Characteristics - Twin Screw
4.6 - Worked Example – Evaluation of a Proposed Screw Profile (Twin Screw)
4.7 - Basic Considerations when preparing a Screw Profile

5. Die Design & Extruder Operating Curves
5.1 The Pipe Flow Analogy
5.2 The Die Characteristic
5.3 Extruder Operating Curves
5.4 Technical Considerations for Die Design
5.5 Influence of Fluid Rheology upon Die Flow
5.6 The Extrusion System

6. Ingredients in Extrusion Processing
6.1 Starch
6.2 Protein
6.3 Fats and Oils
6.4 Other Ingredient Effects
6.5 Ingredient Functions

7. Role of the Preconditioner in Extrusion
7.1 Functions/Benefits of Preconditioning
7.2 Types of Preconditioner
7.3 Operational Characteristics of Preconditioners
7.4 Residence Time Distribution and Mixing
7.5 Heating and Moisture Diffusion
7.6 Preconditioner Configuration and Speed
7.7 Some Potential Problems

SECTION 2: TECHNOLOGY & APPLICATIONS
8. Understanding Co-Extrusion Technology
8.1 Processing Steps
8.2 Recipe Requirements
8.3 Process Instabilities

9. Texturisation During Extrusion Processing
9.1 Classification of Food Textures
9.2 Product Crispness
9.3 A Mechanism for Developing Texture in Snacks/Cereals
9.4 Control of the Product Texture in Snacks/Cereals
9.5 Protein Texturisation – Textured Vegetable Protein (TVP)
9.6 Protein Texturisation - High Moisture Extrusion Cooking
9.7 Energy Input for Cooking Processes

10. Causes & Effects of Extruder Instabilities
10.1 Irregular Feed Composition
10.2 Irregular Ingredients Feed Rate
10.3 Heating and/or Cooling Fluctuations
10.4 Conveying/Mixing Irregularity
10.5 Partial Blockages
10.6 Die Pressure Drop Too Low
10.7 Irregular Screw Speed and General Mechanical Issues
10.8 Pressure Variations

11. Dynamics of Product Expansion During Extrusion
11.1 The Product Expansion Process
11.2 Elastic Effects and Die Swell
11.3 Bubble Growth Theory and Bubble Structure
11.4 Process Control and Product Expansion

12. Extruded Product Quality Assurance
12.1 What is Product Quality?
12.2 A Review of the Extrusion Process
12.3 The Role of Energy Input
12.4 Requirements for the Process Log Sheet

13. Extrusion Scale-Up & Process Transfer
13.1 Primary and Secondary Scale-up Criteria
13.2 Quantifying the Energy Inputs
13.3 Extruder Scale-up Methodologies
13.4 Die Scale-up Methodology
13.5 Simplified Scale-up Rules

14. Extruder Screw, Barrel & Die-Plate Wear
14.1 Wear Mechanisms
14.2 Effect of Wear on Extruder Performance
14.3 Developing an Extruder Maintenance Cycle
14.4 Some Other Alternatives to Extend the Wear Life of Extruder Components
14.5 Effect of Wear on Product Attributes
14.6 Die Plate Wear

15. Trouble–Shooting Food Extrusion Processes
15.1 Interactive Nature of the Extrusion Process
15.2 A Generic Approach to Troubleshooting
15.3 Identifying Causes of Process Issues
15.4 Melt Fracture
15.5 In-plant Operator Actions

SECTION 3: SPECIAL TOPICS
16. Weighted Average Total Strain (WATS)
16.1 A Method for Quantifying Extrusion Processes
16.2 Extruder Residence Time Distributions
16.3 Extruder Shear Rate and Shear Strain
16.4 Total Strain in the Extruder Die
16.5 The Relationship between Shear Strain and the Total Energy Input
Addendum 16.1 - Estimating WATS for a Single Screw Extruder
Addendum 16.2 - Estimation of Shear Rate for a Two Lobe Kneading Block
Addendum 16.3 - Calculating WATS for a Twin Screw Extruder

17. Single Screw vs. Twin Screw Extruders
17.1 An Engineering Analysis
17.2 Extruder Classification
17.3 Extruder Output Prediction Models
17.4 Velocity Profiles in Different Extruder Types
17.5 Advantages of SSE and TSE
17.6 Further Considerations for the Selection of an Extruder Design

18. An Engineering Analysis of Extruder Venting
18.1 Background
Addendum 18.1 - Dimensional Analysis of Extruder Venting
Addendum 18.2 - Simplified Model for the Venting Section

19. Manufacture of Direct Expanded Snack Foods
19.1 Ingredients for Collet and Friction Disc Extruders
19.2 Design Features of Collet and Friction Disc Extruders
19.3 Operation of the Collet Extruder
19.4 Operation of the Friction Disc Extruder
19.5 Analysis of the Operation of Collet and Friction Disc Extruders
19.6 Summary of the Performance Characteristics of the CE and the FDE

20. Modeling the Degree of Cook in Extruders
20.1 Modeling the Gelatinisation Process
20.2 The Extrusion Cooking Process
20.3 Modeling the Extrusion Cooking Process'
20.4 Gelatinisation vs Cooking
Addendum 20.1 Measurement Methods for the Degree of Cook

21. Example Design/Scale-Up Calculations - a Pet Food
21.1 Comments on formulation development
21.2 Pilot Process Design

APPENDIX – THE FOUR GOLDEN RULES OF EXTRUSION TECHNOLOGY 
Nomenclature and Symbols
References and Textbooks
Index