Extrusion Problems Solved

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

1 What is extrusion cooking?

2 What is cold extrusion?

3 What is dry extrusion?

4 What are the functions of a typical extruder?

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

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

7 What is the waste stream from extrusion processing?

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

9 Can I use extruders as continuous reactors?

10 Do extruders need to be shut down every day?

11 What is feedstock in extrusion?

12 What is a pellet?

13 What is the recipe or formulation?

14 What is the compression ratio?

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

16 What is screw geometry?

17 What does pitch mean?

18 What is the flight depth?

19 What is the flight angle?

20 What does ‘venting concept’ mean?

21 What does shear mean?

22 What are long-cut and short-cut products?

23 What does collet mean?

24 What is kibble?

25 What is starch gelatinization?

26 What is the gelatinization temperature of starch?

27 What is dextrinization?

28 What is the Maillard reaction?

29 What is meant by retention time?

30 What is surging?

31 What are fines?

32 What is meant by grind?

33 What is meant by HTST?

34 What is a PLC?

35 What is the glass transition?

36 What is the melt phase transition?

Chapter 2: Components of a food or feed extrusion system

37 What is a feeder?

38 What is a volumetric feeder?

39 What is a gravimetric feeder?

40 What is a hopper or bin?

41 What is a preconditioned

42 What is a diverter spout?

43 What is an extruder barrel?

44 What does the phrase ‘barrel section’ mean?

45 What is the feeding section of the barrel?

46 What is the compression section of the barrel?

47 What is the metering section of the barrel?

48 What is a barrel liner?

49 What are rifling grooves?

50 What does the term ‘jacket’ mean?

51 What is a screw?

52 What are screw crests and troughs?

53 What is the root?

54 What is a screw element?

55 What is a hollow-core screw?

56 What is a screw flight?

57 What is a continuous flight?

58 What is a cut flight screw?

59 What is an interrupted flight screw?

60 What is the screw bore?

61 What is a worm?

62 What is a shear ring?

63 What are shearing bolts and what are they for?

64 What is a vent in the context of extrusion?

65 What is a die?

66 What is a die insert?

67 What is die land length?

68 What is the die orifice?

69 What is a die plate?

70 What is a choke plate?

71 What is a single-face die plate?

72 What is a breaker plate?

73 What is the cutter?

Chapter 3: Selecting the right type of extruder: single screw and twin screw extruders for food and feed production

74 What are the different types of extruders that are available?

75 What is a single screw extruder?

76 What is a wet extruder?

77 What is a segmented screw/barrel single-screw ‘wet’ extruder?

78 What does a typical single screw consist of?

79 How much internal fat can be present in a recipe to be processed by a single screw extruder?

80 What is the range of particle sizes that can be used in a single screw extruder?

81 What are the typical applications of single screw extruders?

82 What are the pros and cons of single screw extruders?

83 What are the different types of single screw extruder that are available?

84 What are cold forming extruders?

85 What are high-pressure forming extruders?

86 What is a low-shear cooking extruder?

87 What are collet extruders?

88 What are high-shear cooking extruders?

89 What is a twin screw extruder?

90 What are the different types of twin screw extruders that are available?

91 What is the most common design used for twin screw extrusion?

92 Are there any benefits of using twin screw versus a single screw extruder?

93 What is the maximum fat level used in a twin screw extruder?

94 What is the minimum size of the pellet that can be produced with a twin screw extruder?

95 What is the range of particle sizes of raw material that can be used in a twin screw extruder?

96 What is the maximum level of fresh meat that can be incorporated in a recipe to be processed in a twin screw extruder?

97 What are the typical applications of twin screw extruders?

98 What are the disadvantages of using twin screw extruders rather than single screw extruders?

Chapter 4: Selecting the right type of extruder: dry extruders and expanders for food and feed production

99 What is a dry extruder and what does dry extrusion mean?

100 What kinds of ingredients can be processed by a dry extruder?

101 How much moisture loss occurs in dry extrusion?

102 Can we inject water into a dry extruder?

103 Can a preconditioner be used with a dry extruder?

104 What is the basic principle of dry extrusion?

105 What temperatures and pressures can be reached in dry extrusion?

106 What are the main applications of dry extrusion?

107 Are there any other applications of dry extrusion?

108 What are the pros and cons of dry extrusion?

109 What is the main difference between dry and wet extrusion?

110 What are the pros and cons of wet extrusion compared to dry extrusion?

111 What is an interrupted flight extruder?

112 What is an expander?

113 How do interrupted flight extruders differ from other extruders?

114 Do expanders have heating and cooling jackets?

115 What is the main principle behind cooking in expanders?

116 What are the main applications of expanders?

117 Can we remove oil from oilseed crops using expanders?

118 What is the particle size requirement for expanders?

119 Can we add fat in an expander?

120 Can preconditioners be installed on expanders?

121 What are some other applications of expanders?

122 What are the pros and cons of expanders?

123 What is a low cost extruder (LCE)?

124 How do I know what type of extruder I need for my product?

125 What options are available to an extruder buyer?

126 What are the considerations one should keep in mind when buying an extruder?

Chapter 5: Impact of protein, starch, fat and fiber on extruded foods and feeds

127 What is the impact of protein on extruded products in terms of expansion, texture and durability?

128 How can I know if a proteinaceous ingredient will be functional during extrusion?

129 What is a general guideline I can use to determine the functionality of a proteinaceous ingredient?

130 What are examples of proteins that are functional?

131 What are examples of proteins that are not functional?

132 Do all proteins react the same in the extrusion process?

133 At what temperatures do proteins lose their functionality?

134 What does starch contribute to product attributes during extrusion?

135 What levels of starch are typically found in extruded products?

136 Do different starch sources react differently in the extruder?

137 What is the impact of adding more starch to a recipe?

138 Is there a minimum moisture level required during the extrusion of starch?

139 How do I measure how well starch is cooked or gelatinized during extrusion?

140 What are soft and hard types of grains and what impact does this have on the extrusion process?

141 How does fat affect the extrusion process?

142 Is there a difference in impact between different fat sources?

143 Why is fat added to a recipe during extrusion?

144 What other effects do fat levels have on the extrusion process?

145 How can I maximize the level of fat in an extruded product?

146 What is the impact of fiber on extrusion?

147 Are there different types of fiber?

148 Is there a critical particle size for fibrous ingredients?

149 Should I be concerned about acrylamide in extruded products?

150 Should I be concerned about biogenic amines in extruded products?

Chapter 6: Impact of particle size and other ingredients on extruded foods and feeds

151 What is the proper grind or particle size of raw materials for extrusion?

152 What are the benefits of having raw materials with particles of the proper size?

153 What do consumers perceive when extruded products are made with improper size particles?

154 What guidelines can I use to determine the proper particle size of raw materials?

155 What is the impact of using rework in a recipe to be processed by extrusion?

156 How can a recipe be adjusted to make it shelf stable after extrusion and cooling?

157 Which colors or pigments are used in extruded products?

158 Which natural pigments or colors are suitable for use in extruded products?

159 What can be added to the recipe to prevent fat rancidity?

160 What is the effect of extrusion on vitamin stability?

161 What is the effect of extrusion on minerals?

162 Will extrusion control undesirable components in my recipes?

163 What flavorings are used in extruded products?

164 What impact does extrusion have on natural flavorings?

165 Do raw materials (other than flavorings and colorings) contribute any flavor or color to the final products?

166 What impact do calcium carbonate and other similar ingredients have on the extrusion process?

167 What is the impact of adding salt or sugar to a recipe?

168 Why are encapsulated vitamins sometimes used in extrusion? Is encapsulation of vitamins effective?

169 Which extruded products are likely to become rancid if antioxidants and oxygen scavengers are not used?

170 How do I choose which antioxidant and oxygen scavenger to use and at what levels to add them?

171 In what forms are raw materials typically purchased?

Chapter 7: Preconditioners in food and feed extrusion: common problems and their solutions

172 Why doesn’t my preconditioner cook or precondition my product sufficiently?

173 What can I do to increase the retention time in my preconditioned

174 Why does my preconditioner become plugged up at the discharge?

175 How can I reduce the particle size of product coming out of my preconditioner?

176 How can I add higher levels of liquids and slurries to my preconditioner without plugging up the preconditioner at the discharge?

177 Why do my steam injection lines to the preconditioner become plugged?

178 Why do the water spray nozzles become plugged?

179 Why does the preconditioner drive stall or overload during startup?

180 Why is there excess material residue in the preconditioner?

181 Why do I get hard pieces coming out of the preconditioner which later plug the extruder die?

182 Why does steam blow out from the preconditioner vent?

183 Why does product blow out from the preconditioner vent?

184 Is it ever acceptable to close the vent on a preconditioner?

185 What are the features of a typical waste recycling system (WRS)?

186 Why can’t I achieve higher throughputs when I close the vent on the preconditioner?

187 How can I prevent the occurrence of salmonella in the material coming out of the preconditioner?

188 What is the retention time distribution and how is it measured?

189 How can I measure retention time in a preconditioner?

190 Why do I get different product temperature readings even when I have the same process conditions?

191 How do I prevent wear to my preconditioner components?

192 Why does my preconditioner experience corrosion?

193 What is a double-shafted preconditioner?

194 Are vertical preconditioners available and when would this design be useful?

195 What design parameters should I consider when selecting a preconditioner?

196 How does the paddle configuration affect mixing in the preconditioner?

197 When is it not acceptable or necessary to have a preconditioning stage?

198 How do I predict or determine what conditions are required to precondition a new product?

Chapter 8: Single screw extruders in food and feed extrusion: common problems and their solutions

199 Why does product back up into the inlet of the extruder?

200 Why does the extruder overload?

201 What is causing the product to surge – a change in size and shape coming from the extruder?

202 What is the best method of controlling product temperature?

203 Why do product moisture and expansion levels vary when adding steam into the extruder barrel?

204 How do we prevent product from over-expanding from the die?

205 What causes my products to be constantly distorted in shape?

206 How can I increase cook in the extruded product without over-expansion?

207 What causes a burnt appearance and taste in extruded products?

208 How can I maintain proper product density?

209 What causes the extruder to leak along the length of the barrel?

210 Why do my process steam and water injection levels vary during extrusion?

211 How can I read a true product temperature inside the extruder?

212 What causes the extruder barrel to move in an eccentric fashion?

213 How can I eliminate the knocking noise the extruder makes when it is in operation?

214 What causes extruder throughput to decrease over time?

215 The wear on my extruder components is excessive – what can be done about this?

216 How should an extruder be safely restarted after a power outage?

217 How can I increase the range of ingredients processed on the single screw extruder?

218 Who can help me select the proper extruder configuration?

Chapter 9: Twin screw extruders in food and feed extrusion: common problems and their solutions

219 Why does product back up into the inlet of the extruder?

220 Why does the extruder overload?

221 What is causing the product to surge – change in size and shape coming off the twin screw extruder?

222 How do we prevent product from over-expansion from the die?

223 What causes my products to be constantly distorted in shape?

224 What causes a burnt appearance and taste in extruded products?

225 How can I increase cook in the extruded product without over-expansion?

226 How can I maintain proper product density?

227 How can I reduce the cell size in products?

228 Why does product moisture and expansion vary when adding steam into the extruder barrel?

229 What causes the extruder to leak product along the length of the barrel?

230 Why do my process steam and water injection levels vary during extrusion?

231 How can I read a true product temperature inside the extruder?

232 What is the best method of controlling product temperature?

233 What causes the extruder barrel to move in an eccentric fashion?

234 How can a knocking noise be eliminated from the extruder when it is in operation?

235 What causes the extruder throughput to decrease over time?

236 Wear on my extruder components is excessive – what can be done about this?

237 How can I increase the range of ingredients processed on the twin screw extruder?

238 Who can help me select the proper extruder configuration?

239 What is the difference between co-rotating and counter-rotating twin screw extruder designs?

Chapter 10: Die and knife assemblies in food and feed extrusion: common problems and their solutions

240 What causes extruded products to be misshapen?

241 What can cause non-uniform piece sizes?

242 How can product expansion be controlled?

243 Why does product appear to collapse or shrink as it leaves the die?

244 Why are some products thicker on one side than the other?

245 When making a ring shape, what causes one part of the ring to expand greatly and the other not to expand sufficiently?

246 What causes ‘tails’ on individual product pieces?

247 Why do some product shapes break easily?

248 Why do product pieces occasionally have a mushroom-like appearance?

249 What causes light and dark streaks on the side of the product?

250 What causes rough surfaces on the product coming from the die?

251 What can be done to prevent corrosion of the die and knife parts?

252 Why do some knife blades wear out quickly?

253 What causes gouge marks on the surface of the die?

254 What is the optimum knife speed?

255 Why does product leak out between the die plates?

256 Why does the extruder continually plug up at the die during startup?

257 What could cause the die plates to be blown off the end of the extruder during a run?

258 Why does product flow faster on one side of the die plate compared to the other?

259 Why does the product diameter get larger over time?

260 What is die swell and how do I take it into account?

261 How can die flow be streamlined?

262 How can a die be designed to manufacture a product of a particular shape?

263 Where can I get help with designing new die shapes or with die technology in general?

264 What is an on-line variable restrictive die?

Chapter 11: Drying extruded food products: common problems and their solutions

265 Why do extruded food products need to be dried?

266 Why are there so many different types of dryers, and which is the best for drying extruded products?

267 What is the best way to improve moisture uniformity in the final product?

268 Why is controlling process air humidity important?

269 What keeps a dryer from reaching and holding the operating temperature set point?

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?

271 What causes product clumping and how does it affect product quality?

272 How does sanitation affect dryer performance and product quality?

273 What could be the potential cause of a sudden dramatic decrease in production capacity?

274 What causes the energy use of a dryer to increase for a given product over time?

275 How do I predict the drying time required?

276 How can I measure the moisture content of the product?

277 What impact do drying and associated processes such as toasting have on the sensory quality of starch-based extruded products?

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?

279 I have seen both vertical and horizontal dryer designs. Which is best?

Chapter 12: Practical considerations, rules of thumb and solutions to the most common problems in food and feed extrusion

280 What should an operator know about assembling an extruder?

281 Are there any general points that should be taken into account in extruder assembly?

282 What utility checks need to be performed before turning on an extruder?

283 What is the typical startup sequence for an extruder?

284 What is the purpose of the startup procedure?

285 What are the critical points which can help to insure quick and steady startup of an extruder?

286 Where should I add my ingredients during extrusion processing?

287 Why do I need a preconditioner?

288 What causes an extruder to wear?

289 What is the best method for cleaning the extruder and screws after the run?

290 What are some rules of thumb that can be used when developing a formulation for extrusion?

291 What are the rules of thumb regarding size reduction of ingredients?

292 What are the rules of thumb regarding mixing of ingredients for extrusion processing?

293 What are the most common problems that occur during extrusion?

294 Why do these most common problems happen?

295 How can we overcome the most common problems?

296 What causes surging during dry extrusion?

297 What causes wedging during extrusion?

298 What causes a lower feed rate in extrusion?

299 What causes variation in product density during extrusion?

300 What causes product to break or become distorted?

301 What causes color variation during extrusion?

302 How can problems in picking up the product by the screw be reduced?

Index