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Extrusion problems solved: Food, pet food and feed

Edited by M N Riaz and G J Rokey 
Woodhead  November 2011  



Hardback  184 pp  ISBN 9781845696641      £125.00
  • 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

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.

Contents

Introduction to food and feed extrusion and related terminology
What is extrusion cooking? - What is cold extrusion? - What is dry extrusion? - What are the functions of a typical extruder? - What are the advantages of extrusion compared to other thermal processes? - What is the quality of the products produced by extrusion? - What is the waste stream from extrusion processing? - How easy is it to scale up the extrusion process? - Can I use extruders as continuous reactors? - Do extruders need to be shut down every day? - What is feedstock in extrusion? - What is a pellet? - What is the recipe or formulation? - What is the compression ratio? - What is the L/D (Length to Diameter) ratio? - What is screw geometry? - What does pitch mean? - What is the flight depth? - What is the flight angle? - What does "venting concept" mean? - What does shear mean? - What are long-cut and short-cut products? - What does collet mean? - What is kibble? - What is starch gelatinization? - What is the gelatinization temperature of starch? - What is dextrinization? - What is the Maillard Reaction? - What is meant by retention time? - What is surging? - What are fines? - What is meant by grind? - What is meant by HTST? - What is a PLC? - What is the glass transition? - What is the melt phase transition?

Components of a food or feed extrusion system
What is a feeder? - What is a volumetric feeder? - What is a gravimetric feeder? - What is a hopper or bin? - What is a preconditioner? - What is a diverter spout? - What is an extruder barrel? - What does the phrase "barrel section" mean? - What is the feeding section of the barrel? - What is the compression section of the barrel? - What is the metering section of the barrel? - What is a barrel liner? - What are rifling grooves? - What does the term "jacket" mean? - What is a screw? - What are screw crests and troughs? - What is the root? - What is a screw element? - What is a hollow-core screw? - What is a screw flight? - What is a continuous flight? - What is a cut flight screw? - What is an interrupted flight screw? - What is the screw bore? - What is a worm? - What is a shear ring? - What are shearing bolts and what are they for? - What is a vent in the context of extrusion? - What is a die? - What is a die insert? - What is die land length? - What is the die orifice? - What is a die plate? - What is a choke plate? - What is a single-face die plate? - What is a breaker plate? - What is the cutter?

Selecting the right type of extruder: single screw and twin screw extruders for food and feed production
What are the different types of extruder that are available? - What is a single screw extruder? - What is a wet extruder? - What is a segmented screw/barrel single-screw "wet" extruder? - What does a typical single screw extruder consist of? - How much internal fat can be present in a recipe to be processed by a single screw extruder? - What is the range of particle sizes that can be used in a single screw extruder? - What are the typical applications of single screw extruders? - What are the pros and cons of single screw extruders? - What are the different types of single screw extruder that are available? - What are cold forming extruders? - What are high-pressure forming extruders? - What is a low-shear cooking extruder? - What are collet extruders? - What are high-shear cooking extruders? - What is a twin screw extruder? - What are the different types of twin screws extruders that are available? - What is the most common design used for twin screw extrusion? - Are there any benefits of using a twin screw vs. a single screw extruder? - What is the maximum fat level used in a twin screw extruder? - What is the minimum size of the pellet that can be produced with a twin screw extruder? - What is the range of particle sizes of raw material that can be used in a twin screw extruder? - What is the maximum level of fresh meat that can be incorporated in a recipe to be processed in a twin screw extruder? - What are the typical applications of twin screw extruders? - What are the disadvantages of using twin screw extruders rather than single screw extruders?

Selecting the right type of extruder: dry extruders and expanders for food and feed production
What is a dry extruder and what does dry extrusion mean? - What kinds of ingredients can be processed with a dry extruder? - How much moisture loss occurs in dry extrusion? - Can we inject water into a dry extruder? - Can a preconditioner be used with a dry extruder? - What is the basic principle of dry extrusion? - What temperatures and pressures can be reached in dry extrusion? - What are the main applications of dry extrusion? - Are there any other applications of dry extrusion? - What are the pros and cons of dry extrusion? - What is the main difference between dry and wet extrusion? - What are the pros and cons of wet extrusion compared to dry extrusion? - What is an interrupted flight extruder? - What is an expander? - How do interrupted flight extruders differ from other extruders? - Do expanders have heating and cooling jackets? - What is the main principle behind cooking in expanders? - What are the main applications of expanders? - Can we remove oil from oilseed crops using expanders? - What is the particle size requirement for expanders? - Can we add fat in an expander? - Can preconditioners be installed on expanders? - What are some other applications of expanders? - What are the pros and cons of expanders? - What is an LCE extruder? - How do I know what type of extruder I need for my product? - What options are available to an extruder buyer? - What are the considerations one should keep in mind when buying an extruder?

Impact of protein, starch, fat and fiber on extruded foods and feeds
What is the impact of protein on extruded products in terms of expansion, texture, and durability? - How can I know if a proteinaceous ingredient will be functional during extrusion? - What is a general guideline I can use to determine the functionality of a proteinaceous ingredient? - What are examples of proteins that are functional? - What are examples of proteins that are not functional? - Do all proteins react the same in the extrusion process? - At what temperatures do proteins lose their functionality? - What does starch contribute to product attributes during extrusion? - What levels of starch are typically found in extruded products? - Do different starch sources react differently in the extruder? - What is the impact of adding more starch to a recipe? - Is there a minimum moisture level required during the extrusion of starch? - How do I measure how well starch is cooked or gelatinized during extrusion? - What are soft and hard types of grains and what impact does this have on the extrusion process? - How does fat impact the extrusion process? - Is there a difference in impact between different fat sources? - Why is fat added to a recipe during extrusion? - What other effects do fat levels have on the extrusion process? - How can I maximize the level of fat in an extruded product? - What is the impact of fiber on extrusion? - Are there different types of fiber? - Is there a critical particle size for fibrous ingredients? - Should I be concerned about acrylamide in extruded products? - Should I be concerned about biogenic amines in extruded products?

Impact of particle size and other ingredients on extruded foods and feeds
What is the proper grind or particle size of raw materials for extrusion? - What are the benefits of having raw materials with particles of the proper size? - What do consumers perceive when extruded products are made with improper size particles? - What guidelines can I use for determining the proper particle size of raw materials? - What is the impact of using rework in a recipe to be processed by extrusion? - How can a recipe be adjusted to make it shelf stable after extrusion and cooling? - Which colors or pigments are used in extruded products? - Which natural pigments or colors are suitable for use in extruded products? - What can be added to the recipe to prevent fat rancidity? - What is the effect of extrusion on vitamin stability? - What is the effect of extrusion on minerals? - Will extrusion control undesirable components in my recipes? - What flavorings are used in extruded products? - What impact does extrusion have on natural flavorings? - Do raw materials (other than flavorings and colorings) contribute any flavor or color to the final products? - What impact do calcium carbonate and other similar ingredients have on the extrusion process? - What are the impacts of adding salt or sugar to a recipe? - Why are encapsulated vitamins sometimes used in extrusion? Is encapsulation of vitamins effective? - Which extruded products are likely to become rancid if antioxidants and oxygen scavengers are not used? - How do I choose which antioxidant and oxygen scavenger to use and at what levels to add them? - In what forms are the raw materials typically purchased?

Preconditioners in food and feed extrusion: common problems and their solutions
Why does my preconditioner not precondition or cook my product sufficiently? - What can I do to increase retention time in my preconditioner? - Why does my preconditioner plug up at the discharge? - How can I reduce the particle size of product coming out of my preconditioner? - How can I add higher levels of liquids and slurries to my preconditioner without plugging up the preconditioner at the discharge? - Why do my steam injection lines plug on the preconditioner? - Why do the water spray nozzles plug? - Why does the preconditioner drive stall or overload during startup? - Why is there excess material residue in the preconditioner? - Why do I get hard pieces coming out of the preconditioner which later plug the extruder die? - Why does steam blow out of the preconditioner vent? - Why does product blow out of the preconditioner vent? - Is it ever acceptable to close the vent on a preconditioner? - What are the features of a typical waste recycling system (WRS)? - Why can't I achieve higher throughputs when I close the vent on the preconditioner? - How can I prevent the presence of salmonella in the material coming out of the preconditioner? - What is the retention time distribution and how is it measured? - How can I measure retention time in a preconditioner? - Why do I get different product temperature readings even when I have the same process conditions? - How do I prevent wear to my preconditioner components? - Why does my preconditioner experience corrosion? - What is a double-shafted preconditioner? - Are vertical preconditioners available and when would this design be useful? - What design parameters should I consider when selecting a preconditioner? - How does the paddle configuration affect mixing in the preconditioner? - When is it not acceptable or necessary to have a preconditioning stage? - How do I predict or determine what conditions are required to precondition a new product?

Single screw extruders in food and feed extrusion: common problems and their solutions
Why does product back up into the inlet of the extruder? - Why does the extruder overload? - What is causing the product to surge - change in size and shape coming off the extruder? - What is the best method to control product temperature? - Why do both product moisture and expansion levels vary when adding steam into the extruder barrel? - How do we prevent product from over-expanding off the die? - What causes my products to be constantly distorted in shape? - How can I increase cook in the extruded product without overexpansion? - What causes burnt appearance and taste in extruded products? - How can I maintain proper product density? - What causes the extruder to leak along the length of the barrel? - Why do my process steam and water injection levels vary during extrusion? - How can I read a true product temperature inside the extruder? - What causes the extruder barrel to move in an eccentric fashion? - The extruder is making a knocking noise when it is operation. How can I eliminate this? - What causes extruder throughput to decrease over time? - The wear on my extruder components is excessive - what can be done about this? - How should an extruder be safely restarted after a power outage? - How can I increase the range of ingredients processed on the single screw extruder? - Who can help me select the proper extruder configuration?

Twin screw extruders in food and feed extrusion: common problems and their solutions
Why does product back up into the inlet of the extruder? - Why does the extruder overload? - What is causing product to surge - change in size and shape coming off the extruder? - How do we prevent product from over-expanding off the die? - What causes my products to be constantly distorted in shape? - What causes burnt appearance and taste in extruded products? - How can I increase cook in the extruded product without overexpansion? - How can I maintain proper product density? - How can I reduce the cell size in products? - Why does product moisture and expansion vary when adding steam into the extruder barrel? - What causes the extruder to leak along the length of the barrel? - Why do my process steam and water injection levels vary during extrusion? - How can I read a true product temperature inside the extruder? - What is the best method to control product temperature? - What causes the extruder barrel to move in an eccentric fashion? - How can a knocking noise be eliminated from the extruder when it is in operation? - What causes the extruder throughput to decrease over time? - The wear on my extruder components is excessive - what can be done about this? - How can I increase the range of ingredients processed on the twin screw extruder? - Who can help me select the proper extruder configuration? - What is the difference between co-rotating and counter-rotating twin screw extruder designs?

Die and knife assemblies in food and feed extrusion: common problems and their solutions
What causes extruded products to be misshapen? - What can cause non-uniform piece sizes? - How can product expansion be controlled? - Why does product appear to collapse or shrink off the die? - Why are some products thicker on one side than the other? - When making a ring-shape, what causes one part of the ring to greatly expand and the other not to expand sufficiently? - What causes "tails" on individual product pieces? - Why do some product shapes break easily? - Why do product pieces occasionally have a mushroom-like appearance? - What causes light and dark streaks on the side of the product? - What causes rough surfaces on the product coming from the die? - What can be done to prevent corrosion of die and knife parts? - Why do some knife blades wear out quickly? - What causes gouge marks on the surface of the die? - What is the optimum knife speed? - Why does product leak out between the die plates? - Why does the extruder continually plug up at the die during startup? - What could cause the die plates to be blown off the end of the extruder during a run? - Why does product flow faster on one side of the die plate compared to the other? - Why does the product diameter get larger over time? - What is die swell and how do I take it into account? - How can die flow be streamlined? - How can a die be designed to manufacture a product of a particular shape? - Where I get help with designing new die shapes or with die technology in general? - What is an on-line variable restrictive die?

Drying extruded food products: common problems and their solutions
Why do extruded food products need to be dried? - Why are there so many different types of dryers and which is the best for drying extruded products? - What is the best way to improve moisture uniformity in the final product? - Why is controlling process air humidity important? - What keeps a dryer from reaching and holding the operating temperature set point? - Why can mold grow on an extruded product in a sealed package or container when the moisture content is at the target "safe" level? - What causes product clumping and how does it affect product quality? - How does sanitation affect dryer performance and product quality? - What could be the potential cause of a sudden, dramatic decrease in production capacity of a dryer? - What causes the energy use of a dryer to increase for a given product over time? - How do I predict the drying time required? - How can I measure the moisture content of the product? - What impact do drying and associated processes such as toasting have on the sensory quality of starch-based extruded products? - If the moisture content of the final product exiting the dryer is not correct, should I make changes to the process conditions in the extruder or the dryer so that acceptable moisture contents are reached? - I have seen both vertical and horizontal dryer designs. Which is best?

Practical considerations, rules of thumb and solutions to the most common problems in food and feed extrusion
What should an operator know about assembling an extruder? - Are there any general points that should be taken into account for extruder assembly? - What utility checks need to be performed before turning on an extruder? - What is the typical start-up sequence for an extruder? - What is the purpose of the start-up procedure? - What are the critical points which can help to insure a quick and steady start up of an extruder? - Where should I add my ingredients during extrusion processing? - Why do I need a preconditioner? - What causes an extruder to wear? - What is the best method for cleaning the extruder and screws after a run? - What are some rules of thumb that can be used when developing a formulation for extrusion? - What are the rules of thumb regarding size reduction of ingredients? - What are the rules of thumb regarding mixing of ingredients for extrusion processing? - What are the most common problems that occur during extrusion? - Why do these most common problems happen? - How can we overcome these most common problems? - What causes surging during dry extrusion? - What causes wedging during extrusion? - What causes a lower feed rate in extrusion? - What causes variation in product density during extrusion? - What causes product to break or become distorted? - What causes color variation during extrusion? - How can problems in picking up of the product by the screw be reduced?

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