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