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By JF Rickman and M Gummert Agricultural Engineering IRRI

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1 By JF Rickman and M Gummert Agricultural Engineering IRRI
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 Characteristics of rice
Percentage Paddy 100 Husk 20 Brown rice 80 Meal Pericarp and testa (5-6%) Aluerone (1%) Embryo (3%) 8-10 White rice 70-72

5 Chemical Characteristics
Brown rice White rice Bran Moisture content (%) 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 9-10

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 t/hr Milling recovery - 60%

10 2 stage Vietnam mill

11 Multistage Mill 2. Removing the husk or outer layer from the paddy
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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