15 Lecture 24 Nov 2015 Extrusion part 2 - Food extrusion...

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11/26/2015 1 4010 Food Processing II Extrusion Part 2 November 26, 2015 1 Food extrusion Extrusion is a process where raw mixed materials are forced through a cylindrical barrel in order to form, shape and sometimes cook The gelatinised starch ensures that when the mixture expands by going from high pressure to low pressure it holds its expanded shape 2 Food extrusion Extrusion involves simultaneous mixing, kneading and cooking Complex changes to a food: hydration of starches and proteins homogenisation, gelation shearing melting of fats denaturation or re-orientation of proteins, plastification and expansion of the food structure. 3 Technology Types of food extrusion: Cold or cooking Single or twin screw. 4 Cold and cooking extrusions In cold extrusion (T is less 100ºC), the generated heat must be removed to keep the low temperature of a mixing mass. To prevent extensive heat generation, cold extruders operate at lower rotational speeds (1/10 of those of cooker extruders). [e.g. pasta, dough, meat products]. If the food is heated above 100ºC the process is known as extrusion cooking (or hot extrusion ). Extrusion cooking is a high-temperature short-time (HTST) process which reduces microbial contamination and inactivates enzymes. 5 Cold extrusion Cold extrusion In this process, the product is extruded without cooking or distortion of the food. The extruder has a deep-flighted screw, which operates at a low speed in a smooth barrel, to knead and extrude the material with little friction. It is used to produce pasta, hot dogs, pastry doughs and some types of confectionery.
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  • Winter '16
  • Extrusion, hot extrusion, Rheological Properties, extrusion cooking, food extrusion

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