Extrusion Problems Solved

<p>About the authors</p> <p>Woodhead Publishing Series in Food Science, Technology and Nutrition</p> <p>Preface</p> <p>Sources of further information</p> <p>Chapter 1: An introduction to food and feed extrusion and associated terminology</p> <p>1 What is extrusion cooking?</p> <p>2 What is cold extrusion?</p> <p>3 What is dry extrusion?</p> <p>4 What are the functions of a typical extruder?</p> <p>5 What are the advantages of extrusion compared to other thermal processes?</p> <p>6 What is the quality of the products produced by extrusion?</p> <p>7 What is the waste stream from extrusion processing?</p> <p>8 How easy is it to scale up the extrusion process?</p> <p>9 Can I use extruders as continuous reactors?</p> <p>10 Do extruders need to be shut down every day?</p> <p>11 What is feedstock in extrusion?</p> <p>12 What is a pellet?</p> <p>13 What is the recipe or formulation?</p> <p>14 What is the compression ratio?</p> <p>15 What is L/D (length to diameter) ratio?</p> <p>16 What is screw geometry?</p> <p>17 What does pitch mean?</p> <p>18 What is the flight depth?</p> <p>19 What is the flight angle?</p> <p>20 What does ‘venting concept’ mean?</p> <p>21 What does shear mean?</p> <p>22 What are long-cut and short-cut products?</p> <p>23 What does collet mean?</p> <p>24 What is kibble?</p> <p>25 What is starch gelatinization?</p> <p>26 What is the gelatinization temperature of starch?</p> <p>27 What is dextrinization?</p> <p>28 What is the Maillard reaction?</p> <p>29 What is meant by retention time?</p> <p>30 What is surging?</p> <p>31 What are fines?</p> <p>32 What is meant by grind?</p> <p>33 What is meant by HTST?</p> <p>34 What is a PLC?</p> <p>35 What is the glass transition?</p> <p>36 What is the melt phase transition?</p> <p>Chapter 2: Components of a food or feed extrusion system</p> <p>37 What is a feeder?</p> <p>38 What is a volumetric feeder?</p> <p>39 What is a gravimetric feeder?</p> <p>40 What is a hopper or bin?</p> <p>41 What is a preconditioned</p> <p>42 What is a diverter spout?</p> <p>43 What is an extruder barrel?</p> <p>44 What does the phrase ‘barrel section’ mean?</p> <p>45 What is the feeding section of the barrel?</p> <p>46 What is the compression section of the barrel?</p> <p>47 What is the metering section of the barrel?</p> <p>48 What is a barrel liner?</p> <p>49 What are rifling grooves?</p> <p>50 What does the term ‘jacket’ mean?</p> <p>51 What is a screw?</p> <p>52 What are screw crests and troughs?</p> <p>53 What is the root?</p> <p>54 What is a screw element?</p> <p>55 What is a hollow-core screw?</p> <p>56 What is a screw flight?</p> <p>57 What is a continuous flight?</p> <p>58 What is a cut flight screw?</p> <p>59 What is an interrupted flight screw?</p> <p>60 What is the screw bore?</p> <p>61 What is a worm?</p> <p>62 What is a shear ring?</p> <p>63 What are shearing bolts and what are they for?</p> <p>64 What is a vent in the context of extrusion?</p> <p>65 What is a die?</p> <p>66 What is a die insert?</p> <p>67 What is die land length?</p> <p>68 What is the die orifice?</p> <p>69 What is a die plate?</p> <p>70 What is a choke plate?</p> <p>71 What is a single-face die plate?</p> <p>72 What is a breaker plate?</p> <p>73 What is the cutter?</p> <p>Chapter 3: Selecting the right type of extruder: single screw and twin screw extruders for food and feed production</p> <p>74 What are the different types of extruders that are available?</p> <p>75 What is a single screw extruder?</p> <p>76 What is a wet extruder?</p> <p>77 What is a segmented screw/barrel single-screw ‘wet’ extruder?</p> <p>78 What does a typical single screw consist of?</p> <p>79 How much internal fat can be present in a recipe to be processed by a single screw extruder?</p> <p>80 What is the range of particle sizes that can be used in a single screw extruder?</p> <p>81 What are the typical applications of single screw extruders?</p> <p>82 What are the pros and cons of single screw extruders?</p> <p>83 What are the different types of single screw extruder that are available?</p> <p>84 What are cold forming extruders?</p> <p>85 What are high-pressure forming extruders?</p> <p>86 What is a low-shear cooking extruder?</p> <p>87 What are collet extruders?</p> <p>88 What are high-shear cooking extruders?</p> <p>89 What is a twin screw extruder?</p> <p>90 What are the different types of twin screw extruders that are available?</p> <p>91 What is the most common design used for twin screw extrusion?</p> <p>92 Are there any benefits of using twin screw versus a single screw extruder?</p> <p>93 What is the maximum fat level used in a twin screw extruder?</p> <p>94 What is the minimum size of the pellet that can be produced with a twin screw extruder?</p> <p>95 What is the range of particle sizes of raw material that can be used in a twin screw extruder?</p> <p>96 What is the maximum level of fresh meat that can be incorporated in a recipe to be processed in a twin screw extruder?</p> <p>97 What are the typical applications of twin screw extruders?</p> <p>98 What are the disadvantages of using twin screw extruders rather than single screw extruders?</p> <p>Chapter 4: Selecting the right type of extruder: dry extruders and expanders for food and feed production</p> <p>99 What is a dry extruder and what does dry extrusion mean?</p> <p>100 What kinds of ingredients can be processed by a dry extruder?</p> <p>101 How much moisture loss occurs in dry extrusion?</p> <p>102 Can we inject water into a dry extruder?</p> <p>103 Can a preconditioner be used with a dry extruder?</p> <p>104 What is the basic principle of dry extrusion?</p> <p>105 What temperatures and pressures can be reached in dry extrusion?</p> <p>106 What are the main applications of dry extrusion?</p> <p>107 Are there any other applications of dry extrusion?</p> <p>108 What are the pros and cons of dry extrusion?</p> <p>109 What is the main difference between dry and wet extrusion?</p> <p>110 What are the pros and cons of wet extrusion compared to dry extrusion?</p> <p>111 What is an interrupted flight extruder?</p> <p>112 What is an expander?</p> <p>113 How do interrupted flight extruders differ from other extruders?</p> <p>114 Do expanders have heating and cooling jackets?</p> <p>115 What is the main principle behind cooking in expanders?</p> <p>116 What are the main applications of expanders?</p> <p>117 Can we remove oil from oilseed crops using expanders?</p> <p>118 What is the particle size requirement for expanders?</p> <p>119 Can we add fat in an expander?</p> <p>120 Can preconditioners be installed on expanders?</p> <p>121 What are some other applications of expanders?</p> <p>122 What are the pros and cons of expanders?</p> <p>123 What is a low cost extruder (LCE)?</p> <p>124 How do I know what type of extruder I need for my product?</p> <p>125 What options are available to an extruder buyer?</p> <p>126 What are the considerations one should keep in mind when buying an extruder?</p> <p>Chapter 5: Impact of protein, starch, fat and fiber on extruded foods and feeds</p> <p>127 What is the impact of protein on extruded products in terms of expansion, texture and durability?</p> <p>128 How can I know if a proteinaceous ingredient will be functional during extrusion?</p> <p>129 What is a general guideline I can use to determine the functionality of a proteinaceous ingredient?</p> <p>130 What are examples of proteins that are functional?</p> <p>131 What are examples of proteins that are not functional?</p> <p>132 Do all proteins react the same in the extrusion process?</p> <p>133 At what temperatures do proteins lose their functionality?</p> <p>134 What does starch contribute to product attributes during extrusion?</p> <p>135 What levels of starch are typically found in extruded products?</p> <p>136 Do different starch sources react differently in the extruder?</p> <p>137 What is the impact of adding more starch to a recipe?</p> <p>138 Is there a minimum moisture level required during the extrusion of starch?</p> <p>139 How do I measure how well starch is cooked or gelatinized during extrusion?</p> <p>140 What are soft and hard types of grains and what impact does this have on the extrusion process?</p> <p>141 How does fat affect the extrusion process?</p> <p>142 Is there a difference in impact between different fat sources?</p> <p>143 Why is fat added to a recipe during extrusion?</p> <p>144 What other effects do fat levels have on the extrusion process?</p> <p>145 How can I maximize the level of fat in an extruded product?</p> <p>146 What is the impact of fiber on extrusion?</p> <p>147 Are there different types of fiber?</p> <p>148 Is there a critical particle size for fibrous ingredients?</p> <p>149 Should I be concerned about acrylamide in extruded products?</p> <p>150 Should I be concerned about biogenic amines in extruded products?</p> <p>Chapter 6: Impact of particle size and other ingredients on extruded foods and feeds</p> <p>151 What is the proper grind or particle size of raw materials for extrusion?</p> <p>152 What are the benefits of having raw materials with particles of the proper size?</p> <p>153 What do consumers perceive when extruded products are made with improper size particles?</p> <p>154 What guidelines can I use to determine the proper particle size of raw materials?</p> <p>155 What is the impact of using rework in a recipe to be processed by extrusion?</p> <p>156 How can a recipe be adjusted to make it shelf stable after extrusion and cooling?</p> <p>157 Which colors or pigments are used in extruded products?</p> <p>158 Which natural pigments or colors are suitable for use in extruded products?</p> <p>159 What can be added to the recipe to prevent fat rancidity?</p> <p>160 What is the effect of extrusion on vitamin stability?</p> <p>161 What is the effect of extrusion on minerals?</p> <p>162 Will extrusion control undesirable components in my recipes?</p> <p>163 What flavorings are used in extruded products?</p> <p>164 What impact does extrusion have on natural flavorings?</p> <p>165 Do raw materials (other than flavorings and colorings) contribute any flavor or color to the final products?</p> <p>166 What impact do calcium carbonate and other similar ingredients have on the extrusion process?</p> <p>167 What is the impact of adding salt or sugar to a recipe?</p> <p>168 Why are encapsulated vitamins sometimes used in extrusion? Is encapsulation of vitamins effective?</p> <p>169 Which extruded products are likely to become rancid if antioxidants and oxygen scavengers are not used?</p> <p>170 How do I choose which antioxidant and oxygen scavenger to use and at what levels to add them?</p> <p>171 In what forms are raw materials typically purchased?</p> <p>Chapter 7: Preconditioners in food and feed extrusion: common problems and their solutions</p> <p>172 Why doesn’t my preconditioner cook or precondition my product sufficiently?</p> <p>173 What can I do to increase the retention time in my preconditioned</p> <p>174 Why does my preconditioner become plugged up at the discharge?</p> <p>175 How can I reduce the particle size of product coming out of my preconditioner?</p> <p>176 How can I add higher levels of liquids and slurries to my preconditioner without plugging up the preconditioner at the discharge?</p> <p>177 Why do my steam injection lines to the preconditioner become plugged?</p> <p>178 Why do the water spray nozzles become plugged?</p> <p>179 Why does the preconditioner drive stall or overload during startup?</p> <p>180 Why is there excess material residue in the preconditioner?</p> <p>181 Why do I get hard pieces coming out of the preconditioner which later plug the extruder die?</p> <p>182 Why does steam blow out from the preconditioner vent?</p> <p>183 Why does product blow out from the preconditioner vent?</p> <p>184 Is it ever acceptable to close the vent on a preconditioner?</p> <p>185 What are the features of a typical waste recycling system (WRS)?</p> <p>186 Why can’t I achieve higher throughputs when I close the vent on the preconditioner?</p> <p>187 How can I prevent the occurrence of salmonella in the material coming out of the preconditioner?</p> <p>188 What is the retention time distribution and how is it measured?</p> <p>189 How can I measure retention time in a preconditioner?</p> <p>190 Why do I get different product temperature readings even when I have the same process conditions?</p> <p>191 How do I prevent wear to my preconditioner components?</p> <p>192 Why does my preconditioner experience corrosion?</p> <p>193 What is a double-shafted preconditioner?</p> <p>194 Are vertical preconditioners available and when would this design be useful?</p> <p>195 What design parameters should I consider when selecting a preconditioner?</p> <p>196 How does the paddle configuration affect mixing in the preconditioner?</p> <p>197 When is it not acceptable or necessary to have a preconditioning stage?</p> <p>198 How do I predict or determine what conditions are required to precondition a new product?</p> <p>Chapter 8: Single screw extruders in food and feed extrusion: common problems and their solutions</p> <p>199 Why does product back up into the inlet of the extruder?</p> <p>200 Why does the extruder overload?</p> <p>201 What is causing the product to surge – a change in size and shape coming from the extruder?</p> <p>202 What is the best method of controlling product temperature?</p> <p>203 Why do product moisture and expansion levels vary when adding steam into the extruder barrel?</p> <p>204 How do we prevent product from over-expanding from the die?</p> <p>205 What causes my products to be constantly distorted in shape?</p> <p>206 How can I increase cook in the extruded product without over-expansion?</p> <p>207 What causes a burnt appearance and taste in extruded products?</p> <p>208 How can I maintain proper product density?</p> <p>209 What causes the extruder to leak along the length of the barrel?</p> <p>210 Why do my process steam and water injection levels vary during extrusion?</p> <p>211 How can I read a true product temperature inside the extruder?</p> <p>212 What causes the extruder barrel to move in an eccentric fashion?</p> <p>213 How can I eliminate the knocking noise the extruder makes when it is in operation?</p> <p>214 What causes extruder throughput to decrease over time?</p> <p>215 The wear on my extruder components is excessive – what can be done about this?</p> <p>216 How should an extruder be safely restarted after a power outage?</p> <p>217 How can I increase the range of ingredients processed on the single screw extruder?</p> <p>218 Who can help me select the proper extruder configuration?</p> <p>Chapter 9: Twin screw extruders in food and feed extrusion: common problems and their solutions</p> <p>219 Why does product back up into the inlet of the extruder?</p> <p>220 Why does the extruder overload?</p> <p>221 What is causing the product to surge – change in size and shape coming off the twin screw extruder?</p> <p>222 How do we prevent product from over-expansion from the die?</p> <p>223 What causes my products to be constantly distorted in shape?</p> <p>224 What causes a burnt appearance and taste in extruded products?</p> <p>225 How can I increase cook in the extruded product without over-expansion?</p> <p>226 How can I maintain proper product density?</p> <p>227 How can I reduce the cell size in products?</p> <p>228 Why does product moisture and expansion vary when adding steam into the extruder barrel?</p> <p>229 What causes the extruder to leak product along the length of the barrel?</p> <p>230 Why do my process steam and water injection levels vary during extrusion?</p> <p>231 How can I read a true product temperature inside the extruder?</p> <p>232 What is the best method of controlling product temperature?</p> <p>233 What causes the extruder barrel to move in an eccentric fashion?</p> <p>234 How can a knocking noise be eliminated from the extruder when it is in operation?</p> <p>235 What causes the extruder throughput to decrease over time?</p> <p>236 Wear on my extruder components is excessive – what can be done about this?</p> <p>237 How can I increase the range of ingredients processed on the twin screw extruder?</p> <p>238 Who can help me select the proper extruder configuration?</p> <p>239 What is the difference between co-rotating and counter-rotating twin screw extruder designs?</p> <p>Chapter 10: Die and knife assemblies in food and feed extrusion: common problems and their solutions</p> <p>240 What causes extruded products to be misshapen?</p> <p>241 What can cause non-uniform piece sizes?</p> <p>242 How can product expansion be controlled?</p> <p>243 Why does product appear to collapse or shrink as it leaves the die?</p> <p>244 Why are some products thicker on one side than the other?</p> <p>245 When making a ring shape, what causes one part of the ring to expand greatly and the other not to expand sufficiently?</p> <p>246 What causes ‘tails’ on individual product pieces?</p> <p>247 Why do some product shapes break easily?</p> <p>248 Why do product pieces occasionally have a mushroom-like appearance?</p> <p>249 What causes light and dark streaks on the side of the product?</p> <p>250 What causes rough surfaces on the product coming from the die?</p> <p>251 What can be done to prevent corrosion of the die and knife parts?</p> <p>252 Why do some knife blades wear out quickly?</p> <p>253 What causes gouge marks on the surface of the die?</p> <p>254 What is the optimum knife speed?</p> <p>255 Why does product leak out between the die plates?</p> <p>256 Why does the extruder continually plug up at the die during startup?</p> <p>257 What could cause the die plates to be blown off the end of the extruder during a run?</p> <p>258 Why does product flow faster on one side of the die plate compared to the other?</p> <p>259 Why does the product diameter get larger over time?</p> <p>260 What is die swell and how do I take it into account?</p> <p>261 How can die flow be streamlined?</p> <p>262 How can a die be designed to manufacture a product of a particular shape?</p> <p>263 Where can I get help with designing new die shapes or with die technology in general?</p> <p>264 What is an on-line variable restrictive die?</p> <p>Chapter 11: Drying extruded food products: common problems and their solutions</p> <p>265 Why do extruded food products need to be dried?</p> <p>266 Why are there so many different types of dryers, and which is the best for drying extruded products?</p> <p>267 What is the best way to improve moisture uniformity in the final product?</p> <p>268 Why is controlling process air humidity important?</p> <p>269 What keeps a dryer from reaching and holding the operating temperature set point?</p> <p>270 Why can mold grow on an extruded product in a sealed package or container when the moisture content is at the target ‘safe’ level?</p> <p>271 What causes product clumping and how does it affect product quality?</p> <p>272 How does sanitation affect dryer performance and product quality?</p> <p>273 What could be the potential cause of a sudden dramatic decrease in production capacity?</p> <p>274 What causes the energy use of a dryer to increase for a given product over time?</p> <p>275 How do I predict the drying time required?</p> <p>276 How can I measure the moisture content of the product?</p> <p>277 What impact do drying and associated processes such as toasting have on the sensory quality of starch-based extruded products?</p> <p>278 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?</p> <p>279 I have seen both vertical and horizontal dryer designs. Which is best?</p> <p>Chapter 12: Practical considerations, rules of thumb and solutions to the most common problems in food and feed extrusion</p> <p>280 What should an operator know about assembling an extruder?</p> <p>281 Are there any general points that should be taken into account in extruder assembly?</p> <p>282 What utility checks need to be performed before turning on an extruder?</p> <p>283 What is the typical startup sequence for an extruder?</p> <p>284 What is the purpose of the startup procedure?</p> <p>285 What are the critical points which can help to insure quick and steady startup of an extruder?</p> <p>286 Where should I add my ingredients during extrusion processing?</p> <p>287 Why do I need a preconditioner?</p> <p>288 What causes an extruder to wear?</p> <p>289 What is the best method for cleaning the extruder and screws after the run?</p> <p>290 What are some rules of thumb that can be used when developing a formulation for extrusion?</p> <p>291 What are the rules of thumb regarding size reduction of ingredients?</p> <p>292 What are the rules of thumb regarding mixing of ingredients for extrusion processing?</p> <p>293 What are the most common problems that occur during extrusion?</p> <p>294 Why do these most common problems happen?</p> <p>295 How can we overcome the most common problems?</p> <p>296 What causes surging during dry extrusion?</p> <p>297 What causes wedging during extrusion?</p> <p>298 What causes a lower feed rate in extrusion?</p> <p>299 What causes variation in product density during extrusion?</p> <p>300 What causes product to break or become distorted?</p> <p>301 What causes color variation during extrusion?</p> <p>302 How can problems in picking up the product by the screw be reduced?</p> <p>Index</p>