Rice Grain Quality
By JF Rickman and M Gummert,
IRRI, Los Banos
Philippines
What is rice quality?
Rice quality is a
combination of
physical and
chemical
characteristics
which are required
for a specific use
by a specific user.
Genetic Properties
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Chemical characteristics
Shape
Size
Color
Chalkiness
Bulk density
Thermal conductivity
Equilibrium Moisture
Content
• Flow ability
Acquired properties
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Moisture content
Grain purity
Pest damage
Physical damage
Immature grains
Milling
characteristics
• Chalkiness
Quality Characteristics
Genetic
Acquired
• chemical characteristics such
as gelatinization temperature,
gel consistency, and aroma
• moisture content
• grain shape and size
• color and chalkiness
• bulk density
• purity
• thermal conductivity
• damage
• equilibrium moisture content
• cracked grains
• immature grains
• milling-related characteristics (head
rice recoveries, whiteness and
milling degree) are also included as
relevant measures of quality because
they are of concern to consumers
Paddy rice characteristics
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Moisture content
Degree purity
Varietal purity
Grain dimensions
Cracked grains
Immature grains
Damaged grains
Milled rice characteristics
Physical characteristics
• Milling degree
• Whiteness
• Translucency
• Grain length
• Foreign material
• Head rice
• Chalkiness
Chemical characteristics
• Amylose content
• Gelatinization
temperature
• Gel consistency
Milling Degree
• Amount of bran removed in milling process
• Measured by whiteness meter or amount in
weight of bran removed
Whiteness
A combination of
• Varietal physical
characteristics
• Post harvest
management and
• Degree of milling.
Head rice
• The amount of whole kernels
after milling
• A whole kernel is 75% +
Chalkiness
• Endosperm opacity or
white belly
• Opaqueness has an
overall chalky texture
caused by interruption
of final filling of the
grain.
• Loosely packed
starch cells
Grain length
• Length to width ratio
stable varietal
property
• Japonica-short and
bold
• Indicia long and
slender
Foreign matter content
• Purity is related to the
presence of dockage in the
grain.
• Dockage refers to material
other than paddy and
includes chaff, stones, weed
seeds, soil, rice straw, stalks
Milled Rice Standards
(Philippines)
GRADE
Grade Specifications
Premium
Grade 1
Grade 2
Grade 3
Head rice (min %)
95.00
80.00
65.00
50.00
Brokens (max %)
4.90
19.75
34.50
49.00
Brewers (max %)
0.10
0.25
0.50
1.00
0
0.50
2.00
0.25
2.00
5.00
0.50
4.00
10.00
2.00
8.00
15.00
0
1.00
0
1
14.00
0.25
3.00
0.10
8
14.00
0.50
5.00
0.20
10
14.00
2.00
10.00
0.50
15
14.00
Defectives:

Damaged grains, max %

Discolored grains, max %

Chalky and immature grains,
max %

Red grains, max %

Red streaked grains, max %
Foreign matter (max 5)
Paddy (max no./kg)
Moisture content (max %)
Chemical characteristics of milled
rice
Gel consistency
measures the
tendency of the
cooked rice to
harden on cooling.
Gelatinization
temperature
determines the
time required for
cooking the rice
High amylose content?
Rice grains cook dry, are less tender, and
become hard upon cooling.
Low-amylose content?
Rice grains cook moist and are sticky
Amylose content
Classified as :
• Waxy (1-2%)
• Non waxy (>2%)
• Very low (2-9%)
• Low (10-20%)
• Intermediate (20-25%)
• High (25-30%)
High amylose
• High volume expansion, dry
and flaky during cooking,
hard upon cooling
Amylose Content
25-30% amylose
content is classified as
High
Intermediate amylose rice
is preferred in most ricegrowing areas of the world
except where low amylose japonicas are
grown
20-25% amylose
content is classified as
Intermediate.
10-20% amylose
content is classified as
Low
10%
HIGH
MEDIUM
LOW
20%
30%
Gelantization temperature
• Time required for cooking
• Measured by alkali spread
factor
• Environment affect- higher
temperature during growing
high gelatinization
temperature
Classification:
• 1-2 high (74.5-80oc),
• 3, high intermediate,
• 4-5, intermediate (70-74oC),
6-7, low (<70oC
Gel Consistency
If
then
Gel
Cooked rice tends to be less sticky.
consistency Harder gel consistency is associated
is hard,
with harder cooked rices and this
feature is particularly evident in highamylose rice.
Gel
Cooked rice has a higher degree of
consistency tenderness. This is a preferred
is soft,
characteristic
Classificat Length of gel
ion
(mm)
Hard
27-35
Medium
Hard
36-40
Medium
41-60
Soft
61-100
Maintaining and improving grain
quality
• Variety
• Crop management
• Post production
Variety Selection
• Short and medium type
grains produce higher head
yield
• Earlier maturing varieties
produce less head rice than
late maturing varieties
• Uniform filling varieties have
higher grain density and less
chalkiness
• Flower unevenly also ripen
unevenly.
Crop Management
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Water control
Nutrient balance
Weeds
Even plant
establishment
• Correct plant
population
• Harvested on time
Harvest management
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Threshing
Drying
Storage
Milling
Market
The fun now begins