riceQuality

Procedures for Measuring quality of milled rice

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Milling degree

Milling degree is computed based on the amount of bran removed from the brown rice. To obtain the weight of brown rice, dehull the paddy samples using the Laboratory Huller.

Estimate the percent milling degree using the following equation:

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Milling recovery

Using the Abrasive Whitener, mill the dehulled samples.  Compute milling recovery by dividing the weight of milled rice recovered by the weight of the paddy sample, as follows:

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Dockage in Milled Rice

Select, segregate and weigh the foreign matter.  Record the number of unhulled grains collected from the sample.  Determine the percentage of dockage of milled rice using the equation:

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Broken grain

Using the Grain Grader, separate the broken grain from the whole grains.  Compute the percentage of the head rice and brokens using the following equations:

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Chalkiness

A visual rating of the chalky proportion of the grain is used to measure chalkiness based on the standard Evaluation System SES  scale presented below:

 

Scale

% area of chalkiness

1

less than 10

5

20-Oct

9

more than 20

Select, segregate and weigh the chalky grains (SES Scale 9).  Determine the % chalky grain using the equation:

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Whiteness

Measure the grain whiteness using the Whiteness Meter.  Separate and weigh yellow-fermented grains.  Calculate the percentage of yellow/fermented grains using the formula:

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Grain Shape

Follow the procedure of determining grain shape of paddy.  Based on the length to width ratio, the shape of the milled rice will be determined. L/W ration is given by:

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The ISO Classification is as follows:

 

Scale

Shape

L/W ratio

1

Slender

Over 3.0

3

Medium

2.1 – 3.0

5

Bold

1.1 – 2.0

9

Round

1.0 or less

 

1000 grain weight

Count and weigh 1,000 whole grains.

Amylose content

Select twenty grains and ground them in a Cyclone Mill.  Amylose content is analyzed using the simplified iodine colorimetric procedure. Samples are categorized into low, intermediate and high based on the following grouping:

 

Category

%Amylose Content

Waxy

2-Jan

Very low amylose

9-Feb

Low

20-Oct

Intermediate

20-25

High

25-30

 

Gelatinization temperature (GT)

GT is measured by determining the alkali-spreading value for which the alkali digestibility test is employed.  Grains are soaked in 1.7% KOH and incubated in a 30oC oven for 23 hours.  Measurement ranges are based on the following: Gelatinization temperature is estimated by the extent of alkali spreading and clearing of milled rice soaked in 1.7% KOH at room temperature or at 39oC for 23 hours.  The degree of spreading is measured using a seven-point scale as follows:

  1. grain not affected
  2. grain swollen,
  3. grain swollen, collar incomplete and narrow,
  4. grain swollen, collar complete and wide,
  5. grain split or segmented, collar complete and wide,
  6. grain dispersed, merging with collar; and
  7. grain completely dispersed and intermingled.

 

Category

Temp ranges (oC)

Alkali Spreading Value

Low

55-69

7-Jun

Intermediate

70-74

5-Apr

High

75-79

3-Feb

 

Gel consistency

Select from two to 10 grains and ground separately in the Wig-L Bug.  Gel consistency is measured by the cold gel in a horizontally-held test tube, for one hour.  Measurement ranges and category  are as follows:

 

Category

Consistency, mm

Soft

61-100

Medium

41-60

Hard

26-40