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

Table of Contents:

Preface
1. Overview of the Extrusion Process    3
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    15
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 and Flow in Extrusion Processing    29
3.1 A Definition for Fluid Viscosity
3.2 Viscoelasticity
3.3 Flow Components in an Extruder Screw
4. Die Design and Extruder Operating Curves    45
4.1 The Pipe Flow Analogy
4.2 The Die Characteristic
4.3 Extruder Operating Curves
4.4 Technical Considerations for Die Design
4.5 Influence of Fluid Rheology upon Die Flow
4.6 The Extrusion System
5. Ingredients in Extrusion Processing    61
5.1 Starch
5.2 Protein
5.3 Fats and Oils
5.4 Other Ingredient Effects
5.5 Ingredient Functions
6. Role of the Preconditioner in Extrusion    89
6.1 Functions/Benefits of Preconditioning
6.2 Types of Preconditioner
6.3 Operational Characteristics of Preconditioners
6.4 Residence Time Distribution and Mixing
6.5 Heating and Moisture Diffusion
6.6 Preconditioner Configuration and Speed
6.7 Some Potential Problems
Section 2: TECHNOLOGY AND APPLICATIONS
7. Understanding Co-Extrusion Technology    107
7.1 Processing Steps    108
7.2 Recipe Requirements    114
7.3 Process Instabilities    115
8. Texturisation during Extrusion Processing    117
8.1 Classification of Food Textures
8.2 Product Crispness
8.3 A Mechanism for Developing Texture in Snacks/Cereals
8.4 Control of the Product Texture in Snacks/Cereals
8.5 Protein Texturisation – Textured Vegetable Protein (TVP)
8.6 Protein Texturisation - High Moisture Extrusion Cooking
8.7 Energy Input for Cooking Processes
9. Causes and Effects of Extruder Instabilities    139
9.1 Irregular Feed Composition
9.2 Irregular Ingredients Feed Rate
9.3 Heating and/or Cooling Fluctuations
9.4 Conveying/Mixing Irregularity
9.5 Partial Blockages
9.6 Die Pressure Drop Too Low
9.7 Irregular Screw Speed and General Mechanical Issues
9.8 Pressure Variations
10. Dynamics of Product Expansion during Extrusion    153
10.1 The Product Expansion Process
10.2 Elastic Effects and Die Swell
10.3 Bubble Growth Theory and Bubble Structure
10.4 Process Control and Product Expansion
11. Extruded Product Quality Assurance    163
11.1 What is Product Quality?
11.2 A Review of the Extrusion Process
11.3 The Role of Energy Input
11.4 Requirements for the Process Log Sheet
12. Extrusion Scale-Up and Process Transfer    171
12.1 Primary and Secondary Scale-up Criteria
12.2 Quantifying the Energy Inputs
12.3 Extruder Scale-up Methodologies
12.4 Die Scale-up Methodology
12.5 Simplified Scale-up Rules
13. Extruder Screw, Barrel and Die-Plate Wear    189
13.1 Wear Mechanisms
13.2 Effect of Wear on Extruder Performance
13.3 Developing an Extruder Maintenance Cycle
13.4 Some Other Alternatives to Extend the Wear Life of Extruder Components
13.5 Effect of Wear on Product Attributes
13.6 Die Plate Wear
14. Trouble–Shooting Food Extrusion Processes    205
14.1 Interactive Nature of the Extrusion Process
14.2 A Generic Approach to Troubleshooting
14.3 Identifying Causes of Process Issues
14.4 Melt Fracture
14.5 In-plant Operator Actions
Section 3: SPECIAL TOPICS
15. Weighted Average Total Strain (WATS)    223
A Method for Quantifying Extrusion Processes
15.1 Extruder Residence Time Distributions
15.2 Extruder Shear Rate and Shear Strain
15.3 The Relationship between Shear Strain and the Total Energy Input
Addendum 15.1 - Estimating WATS for a Single Screw Extruder
Addendum 15.2 - Estimation of Shear Rate for a Two Lobe Kneading Block
16. Single Screw vs. Twin Screw Extruders    235
An Engineering Analysis
16.1 Extruder Classification
16.2 Extruder Output Prediction Models
16.3 Velocity Profiles in Different Extruder Types
16.4 Advantages of SSE and TSE
16.5 Further Considerations for the Selection of an Extruder Design
17. An Engineering Analysis of Extruder Venting    245
17.1 Background
Addendum 17.1 - Dimensional Analysis of Extruder Venting
Addendum 17.2 - Simplified Model for the Venting Section
18. Manufacture of Direct Expanded Snack Foods    261
18.1 Ingredients for Collet and Friction Disc Extruders
18.2 Design Features of Collet and Friction Disc Extruders
18.3 Operation of the Collet Extruder
18.4 Operation of the Friction Disc Extruder
18.5 Analysis of the Operation of Collet and Friction Disc Extruders
18.6 Summary of the Performance Characteristics of the CE and the FDE
19. Modeling the Degree of Cook in Extruders    277
19.1 Modeling the Gelatinisation Process
19.2 The Extrusion Cooking Process
19.3 Modeling the Extrusion Cooking Process
20. Example Design/Scale-Up Calculations - a Pet Food    283
20.1 Comments on formulation development
20.2 Pilot Process Design
APPENDIX – THE FOUR GOLDEN RULES OF EXTRUSION TECHNOLOGY    299
Nomenclature and Symbols
References and Textbooks
Index

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