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Rice Milling

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Remove the bran layers. Produce whole white rice kernels that are. sufficiently milled, ... 3. Polishing or whiting the brown rice to remove the bran layer ... – PowerPoint PPT presentation

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Title: Rice Milling


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 Characteristics of rice
5
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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