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Rice Milling

Rice Milling. By JF Rickman and M Gummert Agricultural Engineering IRRI. Topics. What is milling Characteristic of paddy Options for milling Multistage milling By products of milling. Objective of milling. Remove the husk Remove the bran layers

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Rice Milling

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  1. Rice Milling By JF Rickman and M Gummert Agricultural Engineering IRRI

  2. Topics • What is milling • Characteristic of paddy • Options for milling • Multistage milling • By products of milling

  3. Objective of milling • Remove the husk • Remove the bran layers • Produce whole white rice kernels that are • sufficiently milled, • free of impurities and • minimum number of broken kernels.

  4. Physical characteristic Percentage Paddy 100 Husk 20 Brown rice 80 Meal Pericarp and testa (5-6%) Aluerone (1%) Embryo (3%) 8-10 White rice 70-72 Physical Characteristics of rice

  5. Brown rice White rice Bran Moisture content (%) 13-14 13-14 13-14 Starch (%) Amylose 68-70 80 9 28-30 33 6 Protein (%) 6-8 6-7 14 Fat 3 1 20 Fiber 2-3 0.5 25 Crude ash 1-1.5 0.5 9-10 Chemical Characteristics

  6. Milling Options • Hand Milling • One step milling process • Two-step process and • Multistage process

  7. Pestle and mortar • Friction based-kernel against kernel • High breakage • Final cleaning hand winnowing and gravity

  8. Single pass steel mill • Steel friction mill • Very high pressure • Originated from coffee grinder • Low white rice recovery ( 50-55%) • Head rice less than 30% • Often used for par boiled rice

  9. Two Stage Mill • Super seeded Engleberg (steel) mill • Separate hulling and whitening • Rubber roller huller • Steel friction polisher • Capacity 0.5-1t/hr • Milling recovery - 60%

  10. 2 stage Vietnam mill

  11. Multistage Mill 1.Pre-cleaning the paddy prior to milling 2.  Removing the husk or outer layer from the paddy 3.  Polishing or whiting the brown rice to remove the bran layer 4.  Separating the broken grains from the whole kernels 5.  Bagging the milled rice 6. Managing the by-products

  12. Multi-stage mill

  13. Pre-cleaning Equipment • Oscillating Sieve type • Aspiration cum Oscillation Type • Rotary Cleaner

  14. Process of separation Process • Scalp larger objects • Retain desired size/weight • Removes small size or lighter weight material

  15. De-stoner • Gravity separator • Separates on weight

  16. Dehusker Equipment • Steel huller • Under runner disc sheller • Rubber rollers Operation • Friction between surfaces • Speed differentials • Abrasion

  17. Under runner disc Sheller

  18. Paddy separator Compartment Separator • Paddy and brown rice move at different speeds • Brown rice moves faster • Specific gravity/buoyancy • 45 compartments/2 ton

  19. Gravity separator Tray Separator • Brown rice up slope, paddy down • Specific gravity, grain length, coefficient of friction

  20. Friction polisher • Grain kernels forced against each other and a metal screen by a steel ribbed cylinder • Always horizontal • High pressure, higher temperature than abrasive • Suitable japonica types

  21. Steel Polisher-horizontal friction (Engelberg Type) Feed Steel mesh Steel rotor Grain

  22. Abrasive polisher • Vertical or horizontal • Abrasive surface and screen • Less pressure on kernel • Better for Indica types

  23. Polishing- Conical Stone

  24. Polisher-horizontal Abrasive

  25. Oscillating Screen separator • Separates out brewers • Large and small brokens • Oscillating screen

  26. Length Grader • Length grader works by matching screen indentation with whole grain length • Small/broken rice fall into indents while whole grain pass to end • Sometime set up with 2 different indent sizes

  27. Separating bins • Separates into head rice, large brokens and small broken • Mix any combination on belt by variable speed delivery motors in each outlet

  28. Mist Polisher • Improves luster on rice • Small amount dust and water

  29. Color sorter • Has to be calibrated for desired color • Works on separation discolored grain by using air stream • Expensive

  30. Bagging Station • Rice normally sold in 50kg bags • Accurately weighed

  31. Mill by products • Husk • Coarse meal • Fine meal • Brewers grain

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