Extrusion Problems Solved

Food, Pet Food and Feed

M N Riaz, G J Rokey

• Publisher: Woodhead Publishing
• Year: 2011
• Print ISBN: 9781845696641
• eBook ISBN: 9780857095206
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Extrusion is widely used for the preparation of a variety of foodstuffs including breakfast cereals, snack food and pasta, as well as pet food and animal and aquaculture feed. Extrusion problems solved provides responses to more than 300 frequently asked questions about the process of food extrusion and the techniques and equipment involved, in a practical question-and-answer format.The book is divided into twelve chapters for ease of reference: the opening chapters concentrate on introductory queries and on different components of an extruder system, followed by two chapters that help the reader select the correct type of extruder for a product. Chapters five and six discuss the impact of factors such as protein content and particle size on the extrusion process, while the use of pre-conditioners is discussed in chapter seven. The latter part of the book discusses specific types of extruder and die and knife assemblies, followed by a chapter on issues relating to drying extruded food products. The final chapter offers practical guidelines and rules of thumb for the most common issues relating to food and feed extrusion.Written by two leading experts in the field, Extrusion problems solved is an essential reference source and troubleshooting guide for professionals working in food, pet food and feed extrusion. It will also be a valuable training resource for students of extrusion.- Offers practical guidelines and rules of thumb for the most common food and feed extrusion problems- Chapters concentrate on introductory queries, types of extruder and components of extruder systems, knife assemblies, the use of pre-conditioners and issues in drying extruded food products- Provides responses to more than 300 frequently asked questions about the processes, equipment and techniques of food extrusion in a practical question-and-answer format

An introduction to food and feed extrusion and associated terminology

1 What is extrusion cooking?

Extrusion cooking is a process in which a food or feed material is forced to flow, under elevated temperature, pressure and shear, through a die.

2 What is cold extrusion?

Cold extrusion refers to cooking of food or feed ingredients at temperatures below 40 °C. The maximum process temperature could be higher in some applications but always stays below 100 °C. If temperatures remain below this level, no steam is formed.

3 What is dry extrusion?

Dry extrusion is when cooking is achieved through friction and at moisture levels that result in final extrudate moistures below 12%.

4 What are the functions of a typical extruder?

Depending upon the type of extruder, different functions can be performed. These include agglomeration of ingredients, expansion, gelatinization, homogenization, dehydration, mixing, pasteurization, protein denaturation, shearing, texture alteration and product shaping.

5 What are the advantages of extrusion compared to other thermal processes?

Extrusion cooking offers several advantages: a variety of products can be made by changing the ingredients and operating conditions, multiple shapes can be created, a variety of textures and colors can be produced, cooking is energy efficient, processing costs are lower, a variety of raw materials from all sources (animal and plant) can be processed, and full automation is a possibility.

6 What is the quality of the products produced by extrusion?

Since extrusion is a high temperature short time (HTST) heating process, it minimizes degradation of food nutrients while improving the digestibility of proteins (by denaturation) and starches (by gelatinization). Extrusion cooking at high temperature also destroys anti-nutritional compounds, that is trypsin inhibitors, and undesirable enzymes, such as lipases, lipoxidases and microorganisms.

7 What is the waste stream from extrusion processing?

Extrusion produces few or no waste streams. This is a very important advantage for the food and feed industries as new environmental regulations are stringent and costly.

8 How easy is it to scale up the extrusion process?

Data obtained from the pilot plant extruders can be used to scale up the extrusion system for commercial production.

9 Can I use extruders as continuous reactors?

Extruders are being used as continuous reactors in several countries for deactivation of aflatoxin in peanut meals and destruction of allergens and toxic compounds in castor seed meal and other oilseed crops.

10 Do extruders need to be shut down every day?

Typically, production extruders operate 24 hours a day, and ‘shutdowns’ for cleanup do not occur except for required sanitation or maintenance.

11 What is feedstock in extrusion?

Feedstock is the material, mixture, or formulation to be processed in extruder.

12 What is a pellet?

A pellet is a discrete particle which is shaped and cut by the extruder. It is called a pellet regardless of its shape.

13 What is the recipe or formulation?

The recipe is the ingredients or mixture to be processed in an extruder to make food, aquatic and livestock feed.

14 What is the compression ratio?

The compression ratio (CR) is the volume of the full flight of the screw at the feed opening divided by volume of the last full flight before discharge. Typical CR ranges are from 1:1 to 5:1.

15 What is L/D (length to diameter) ratio?

This is also called ‘L’ over ‘D’. It is the distance from the internal rear edge to the discharge end of the barrel, divided by the diameter of the bore. Food extruder L/D ratios range from 1:1 to 25:1 (see Fig. 1).

Fig. 1 Barrel and other components.

16 What is screw geometry?

The term screw geometry refers to the screw profile within the extruder. It is a combination of flight lead or pitch, flight angle, flight depth, and flight diameter. The geometry can e...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• About the authors
• Woodhead Publishing Series in Food Science, Technology and Nutrition
• Preface
• Sources of further information
• Chapter 1: An introduction to food and feed extrusion and associated terminology
• Chapter 2: Components of a food or feed extrusion system
• Chapter 3: Selecting the right type of extruder: single screw and twin screw extruders for food and feed production
• Chapter 4: Selecting the right type of extruder: dry extruders and expanders for food and feed production
• Chapter 5: Impact of protein, starch, fat and fiber on extruded foods and feeds
• Chapter 6: Impact of particle size and other ingredients on extruded foods and feeds
• Chapter 7: Preconditioners in food and feed extrusion: common problems and their solutions
• Chapter 8: Single screw extruders in food and feed extrusion: common problems and their solutions
• Chapter 9: Twin screw extruders in food and feed extrusion: common problems and their solutions
• Chapter 10: Die and knife assemblies in food and feed extrusion: common problems and their solutions
• Chapter 11: Drying extruded food products: common problems and their solutions
• Chapter 12: Practical considerations, rules of thumb and solutions to the most common problems in food and feed extrusion
• Index