Rice Grain Quality

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Rice Grain Quality

• By JF Rickman and M Gummert,
• IRRI, Los Banos
• Philippines

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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.

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Genetic Properties

• Chemical characteristics
• Shape
• Size
• Color
• Chalkiness
• Bulk density
• Thermal conductivity
• Equilibrium Moisture Content
• Flow ability

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Acquired properties

• Moisture content
• Grain purity
• Pest damage
• Physical damage
• Immature grains
• Milling characteristics
• Chalkiness

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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
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Paddy rice characteristics

• Moisture content
• Degree purity
• Varietal purity
• Grain dimensions
• Cracked grains
• Immature grains
• Damaged grains

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Milled rice characteristics

• Physical characteristics
• Milling degree
• Whiteness
• Translucency
• Grain length
• Foreign material
• Head rice
• Chalkiness
• Chemical characteristics
• Amylose content
• Gelatinization temperature
• Gel consistency

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Milling Degree

• Amount of bran removed in milling process
• Measured by whiteness meter or amount in weight
  of bran removed

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Whiteness

• A combination of
• Varietal physical characteristics
• Post harvest management and
• Degree of milling.

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Head rice

• The amount of whole kernels after milling
• A whole kernel is 75

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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

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Grain length

• Length to width ratio stable varietal property
• Japonica-short and bold
• Indicia long and slender

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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

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Milled Rice Standards(Philippines)
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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
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Amylose content

• Classified as
• Waxy (1-2)
• Non waxy (gt2)
• 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

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Amylose Content
25-30 amylose content is classified as High
Intermediate amylose rice is preferred in most rice-growing 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
HIGH
MEDIUM
LOW
10
20
30
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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 (lt70oC

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Gel Consistency
If then
Gel consistency is hard, Cooked rice tends to be less sticky. Harder gel consistency is associated with harder cooked rices and this feature is particularly evident in high-amylose rice.
Gel consistency is soft, Cooked rice has a higher degree of tenderness. This is a preferred characteristic
Classification Length of gel (mm)
Hard 27-35
Medium Hard 36-40
Medium 41-60
Soft 61-100
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Maintaining and improving grain quality

• Variety
• Crop management
• Post production

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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.

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Crop Management

• Water control
• Nutrient balance
• Weeds
• Even plant establishment
• Correct plant population
• Harvested on time

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Harvest management

• Threshing
• Drying
• Storage
• Milling
• Market

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The fun now begins