Friday, September 11, 2009

Rice Quality Training Manual 14

Rice Quality Training Manual
10.0 Practical exercises
1. Determine the quality of Milled rice
The following tests will be undertaken in the laboratory to determine the quality of milled rice.
· Moisture content
· Head rice
· Broken
· Color
· Transparency
· Chalkiness
· Cooking test
2. Determine the quality of Paddy or Rough rice
The following tests will be undertaken in the laboratory to determine the quality of paddy rice
· Moisture content
· Purity- Other varieties
· Grain dimensions
· Damaged or broken grains
· Unfilled or immature grains
· Insects
· Weed seeds
· Inert material
3. Testing a Rice mill for performance and quality
We will visit a rice mill and sample the paddy before milling, brown rice after husking and the milled grain after processing. At the same time we will monitor the performance of the rice mill by collecting the outputs from all of the outlets from the mill over a given time period.
That means we will collect and weigh the:
· Head rice
· Course broken
· Fine broken
· Brewers
· Meal and
· Husk
Samples will be collected for 10 minutes from each outlet. An open woven bag will be necessary to collect the husk.
Use the miller’s scales
Sub samples will be taken from each of the outlets so that they can be analyzed in the laboratory
4. Visit a Rice Field
· Evaluate crop management practices and determine the likely affect on grain quality.
Rice Quality Training Manual
Sheet 1 Rice mill performance
Date ……………………………..
Name ……………………………..
Address ……………………………..
Other data
Replace rollers (tons) ……………………………..
Reface stones (tons) ……………………………..
Fuel consumption (l/hr) ……………………………..
Storage capacity (tons) ……………………………..
Collecting times. The measuring times will depend on the capacity of the mill. A good benchmark is to collect from each outlet for at least 10 minutes.
Expected outputs. A good quality mill will produce 55% head rice, 15% brokens, 10% bran and 20% husk.
Sampling outputs. Collect a grain sample from the paddy, brown rice and from all stages of the process. Check the list.

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Rice Quality Training Manual
9.0 Appendices 1
International Standards (ISO 7301)
Rice – Specification
1. Scope

This International Standard lays down the minimum specifications for rice (Oryza sativa L.) of the following types: husked rice, husked parboiled rice, milled rice and milled parboiled rice, suitable for human consumption, directly or after reconditioning, and which is the subject of international trade.
2. Normative references
The following standards contain provisions, which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards listed below. Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 712: 1985, Cereals and cereal products – Determination of moisture content (Routine reference method).
ISO 950: 1979, Cereals – Sampling (as grain).
3. Definitions
For the purposes of this International Standard, the following definitions apply.
3.1. paddy: paddy rice: rough rice: Rice retaining its husk after threshing.
3.2. husked rice: cargo rice[1]: Paddy from which the husk only has been removed.
The processes of husking and handling, particularly of parboiled rice, may result in some loss of bran.
3.3. milled rice: Rice obtained after milling which involves removing all or part of the bran and germ from the husked rice.
It could further be classified into the following degrees of milling.
a) undermilled rice: Rice obtained by milling husked rice but not to the degree necessary to mmet the requirements of well-milled rice.
b) well-milled rice: Rice obtained by milling husked rice in such a way that some of the germ, and all the external layers and most of the internal layers of the bran have been removed.
c) extra-well-milled rice: Rice obtained by milling husked rice in such a way that almost all the germ, and all the external layers and the largest part of the internal layers of the bran, and some of the endosperm, have been removed.
3.4. parboiled rice: Rice, the starch of which has been fully gelatinized by soaking paddy or husked rice in water followed by a heat treatment and a drying process.
3.5. glutinous rice: waxy rice: Special varieties of rice (Oryza sativa L. glutinosa) the kernels of which have a white and opaque appearance. The starch of glutinous rice consists almost entirely of amylopectin. It has a tendency to stick together after cooking.
3.6. size of kernels, broken kernels and chips
3.6.1. whole kernel: Kernel without any broken part.
3.6.2. head rice: Kernel, the length of which is greater than or equal to three quarters of the average length of the corresponding whole kernel.
3.6.3. large broken kernel: Fragment of kernel, the length of which is less than three-quarters but greater than one-half of the average length of the corresponding whole kernel.
3.6.4. medium broken kernel: Fragment of kernel, the length of which is less than or equal to one-half but greater than one-quarter of the average length of the corresponding whole kernel.
3.6.5. small broken kernel: Fragment of kernel, the length of which is less than or equal to one-quarter of the average length of the corresponding whole kernel but which does not pass through a metal sieve with round perforations 1.4 mm in diameter.
3.6.6. chip: Fragment of kernel which passes through a metal sieve with round perforations 1.4 mm in diameter.
3.7. extraneous matter: Organic and inorganic components other than kernels of rice, whole or broken
3.8. heat-damaged kernels: Kernels, whole or broken , that have changed their normal color as a result of heating. This category includes whole or broken kernels that are yellow due to alteration. Parboiled rice in a batch of non-parboiled rice is also included in this category.
3.9. damaged kernels: Kernels, whole or broken, showing obvious deterioration due to moisture, pests, disease or other causes, but excluding heat-damaged kernels (3.8).
3.10. immature kernels: Kernels, whole or broken, which are unripe and/or underdeveloped.
3.11. chalky kernels: Kernels, whole or broken, except for glutinous rice, of which at least three-quarters of the surface has an opaque and floury appearance.
3.12. red kernels: Kernels, whole or broken, having a re coloration covering more than one-quarter of their surface, but excluding heat-damaged kernels (3.8).
3.13. red-streaked kernels: Kernels, whole or broken, with red streaks, the lengths of which are greater than or equal to one-half of that of the whole kernel, but where the surface covered by these red streaks is less than one-quarter of the total surface.
3.14. pecks: Kernels, whole or broken, of parboiled rice of which more than one-quarter of the surface is dark brown or black in color.
3.15. other kinds of rice
3.15.1 Paddy in husked rice, in husked parboiled rice, in milled rice and in milled parboiled rice.
3.15.2 Husked rice in husked parboiled rice, in milled rice and in milled parboiled rice.
3.15.3 Milled rice in husked parboiled rice and in milled parboiled rice.
3.15.4 Glutinous in non-glutinous rice.
4. Specification
4.1 General, organoleptic and health characteristics
Kernels of rice, whether or not parboiled, husked or milled, and whether or not whole or broken, shall be sound, clean and free from foreign odors or odor which indicates deterioration.
The levels of additives and pesticide residues and other contaminants shall not exceed the maximum limits permitted by the national regulations of the country of destination or, in their absence, by the joint FAO/WHO Commission of Codes Alimentarius.
The presence of living insects, which are visible to the naked eye, is not permitted.
4.2 Physical and chemical characteristics
4.2.1 The moisture content, determined in accordance with ISO 712, shall be not greater than 15% (m/m)
Note: Lower moisture contents may be required for certain destinations depending on the climate, duration of transport and storage. For further details, see ISO 6322, parts 1, 2 and 3.
4.2.2 The maximum contents of extraneous matter, defective kernels and other kinds of rice in husked and milled rice, whether or not parboiled, and determined in accordance with the method described in annex A, shall be not greater than the values specified in table 1.
4.2.3 All commercial contracts should be clearly the total percentage of broken kernels permitted, classified according to the agreed categories, and the relative proportions of each category, and the total percentage of extraneous matter and of defective kernels, determined in accordance with the method described in Annex A.
The proportion of chips shall not exceed 0.1%.

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Rice Quality Training Manual
8.0 Measurements of chemical characteristics milled rice
Amylose content.
Twenty grains are selected and ground in the UDY 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
Low 10-20
Intermediate 20-25
High 25-30
Gelatinization temperature is measured using alkali-spreading value. The alkali digestibility test is employed. Grains are soaked in 1.7% KOH and incubated in a 30oC oven for 23 hours. Measurement ranges based on the following:
Category Temp ranges (oC) Alkali Spread
Low 55-69 6-7
Intermediate 70-74 4-5
High 75-79 2-3
Gel consistency.
Two to 10 grains are selected and ground separately in the Wig-L Bug. Gel consistency is measured by the cold gel in a test tube, being held horizontally, for one hour. Measurement ranges and category are as follows:
Category Consistency, mm
Soft 61-100
Medium 41-60
Hard 26-40

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Rice Quality Training Manual
7.0 Measuring physical properties of milled rice
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:
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.
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:
Broken grain
Using the Grain Grader, separate the broken grain from the whole grains.
A visual rating of the chalky proportion of the grain is used to measure chalkiness based on the · Select, segregate and weigh the chalky grains (SES Scale 9). Determine the % chalky grain using the equation:
· Measure the grain whiteness using the Whiteness Meter.
· Separate and weigh yellow-fermented grains. Calculate the percentage of yellow/fermented grains using the formula:
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.

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Rice Quality Training Manual
6.0 Measuring physical properties of paddy
Moisture content
Two methods can be used to measure moisture content:
· The primary or direct method ( Air oven method)
· The secondary method (Electronic moisture tester)
Air oven method
· Set the oven at 130oC.
· Weigh three 100 g paddy samples and place the samples inside the oven.
· Measure the final weight of the samples after the 16 hours.
· Compute for the moisture content wet basis (MCWB) using the equation:
· Compute the average MC.
Moisture Tester
· Read the operators instruction
· Turn on the moisture meter and ensure that the machine is set for paddy or rough rice.
· Fill the tray/bowl of the moisture tester with paddy samples.
· Turn/press the knob until the moisture reading is displayed.
· Test at least three samples.
Crack Detector
Using the Paddy Crack Detector, count the number of cracked grains in a 100 grain sample then compute the % cracked grains using the equation:
Grain Dimensions
Using the Vernier caliper or photographic enlarger, collect 20 paddy samples at random from each replicate and measure the dimensions to obtain the average length and width of the paddy grains. To obtain the paddy shape, the following equation will be used.
Paddy will be classified based on International Organization for Standardization (ISO) for paddy.
Immature Grains
· Select a 25 gm grain sample
· Select, segregate and weigh the immature grains in sample. Calculate the percentage immature grains in the sample using the formula:
Remove light foreign matter, stones, weed and seeds from a 100gm sample. Obtain the total weight then compute the dockage percentage as follows:
1000 seed weight
Count and weigh 1,000 grains (paddy).

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Rice Quality Training Manual
5.0 Maintaining Quality
The quality and yield of rice is determined by the variety, the crop management, harvesting, processing and handling.
Different varieties have different physical and chemical characteristics that affect grain quality and yields. The dimension, shape, weight, volume and density of grains determine the physical characteristics of rice and in turn influence head rice yield.
Varieties that:
· Have short and medium type grains, which are more rounded, thicker and harder than long grains produce higher head yield.
· Mature earlier tend to produce less head rice than late maturing varieties.
· Fill uniformly have higher grain density and less chalkiness
· Flower unevenly also ripen unevenly. Non synchronous varieties can have a variation of up to 10% in moisture content and take 5 days longer for the grain to mature at the bottom of the panicle, when compared to the grain in the top of the panicle.
Crop management
The management of the crop will influence the time and uniformity of crop maturity. Basic requirements of good crop management include good water, nutrient, pest and harvest management.
Water management
To be able to manage water, the fields must be level and the bunds or levees well maintained. Uniform water depth across the field will contribute to more uniform crop, higher grain yields and consistent moisture content in the grain sample. Reducing the variation in moisture content at harvest reduces grain fissuring (cracking) and also reduces the chance of spoilage through yellowing and of odors.
Good water management helps reduce weed competition, which not only increases yields but also improves grain quality by reducing dockage levels and reducing moisture
differentials between weed seeds and grain. Wet spots in the grain due to uneven drying or weed seeds can lead to off odors and discoloration of the grain.
Nutrient Management
The application of the correct level and type of fertilizer for the variety and growing conditions is essential. The prudent application of nitrogen is essential to get an even maturing crop with full grain size and high protein levels. Excessive and uneven application of N can stimulate late tiller production, which results in heads on the main culm ripening a number of days faster than the tillers. This will result in more immature and green heads in the sample as well as higher moisture content that increasing the chance of fissuring and spoilage. Conversely insufficient nitrogen can lead to reduced grain size and protein content.
Plant Population
Establishing the correct number of plants is essential to maximize water and nutrient use. A target population that results in 400-500 panicles per m-2 is desirable. This means establishing at least 70-100 seedling m-2 when transplanting, or broadcasting 80-120 kg seed ha-1 when direct seeding.
Low populations may result in:
· increased tillering, which creates more variation in panicle maturity,
· increased weed populations and
· reduces the yield potential of the variety.
High plant populations may reduce yield and quality by:
· competing for water and nutrients,
· mutual shading,
· lodging and
· reduced grain size.

The optimal stage to harvest grain is between 20-25% grain moisture or when 80-85% of the grains are straw colored and the grains in the lower part of the panicle are in the hard doe stage. This is about 30 days after flowering. If the crop is harvested too late, many grains are lost through shattering or drying out and are cracked during threshing. Cracked grains break during milling. If harvested too early, there will be many immature paddy grains and this will reduce head rice yield and quality. The immature rice kernels are very slender and chalky and this results in excessive amount of bran and broken grains. Threshing should occur immediately after cutting as the longer the cut panicles remain in a stack the higher the chance of discoloration or yellowing.
Thresher Machine settings
The correct drum speed settings are needed if grain quality is to be maintained and threshing losses minimized. Drum tip speeds for a peg tooth thresher should be between 12-16 m/sec or approximately 600rpm. Higher speeds result in higher levels of grain damage while lower speeds increase the amount grain retained in the panicle. The fan speed and oscillation speed should be between 800-850 rpm. The clearance between the peg teeth and concave should be about 25 mm.
Paddy or rough rice should be dried to 14% moisture as soon as possible after threshing.
Quality can be maintained by drying and tempering the grain a number of times or in stages during the drying process. This means drying the grain on a drying pad for a number of hours or in the grain dryer and then tempering the grain by allowing it to cool down for a number of hours in a bin or in the bag. This process should be repeated at least a couple of times until the grain is at 14% moisture.
When sun drying the grain should be spread in thin layers (50-100mm) on the pad or floor and be turned and stirred 7-8 times per day. This will even up moisture distribution and increase the rate of drying. Temperatures on drying pads can exceed 508C during the day and this can cause fissuring. To reduce fissuring the paddy may need to be covered during the very hot times of the day or dried over a couple of days.
Grain is also dried in mechanical batch dryers. The most common smaller dryers have a capacity of 1-3 tons per day with drying times of 6-12 hours. For drying of paddy in tropical areas an air temperature of 40-458C is normally used with a heater capable of raising the air temperature 10-158C. An air velocity 0.15-0.25m/s is required and typical
power requirements are 1.5-2.5 kW /ton of paddy. The efficiency of these dryers is also improved by stirring the grain.
Threshed grain contains all kinds of trash. This trash can be vegetable, such as chaff, straw, empty grains and foreign seed as well as mineral materials such as earth and stones. Grain should be cleaned as soon as possible after harvesting and certainly before storage. The simple traditional cleaning method is winnowing, which uses wind or a fan to remove the light elements from the grain. Mechanical winnowers that incorporate a fan and several superimposed reciprocating sieves or screens are now used in many countries. These can be manually powered or motorized and have capacities from 100 kg to 2-3 tons per hour. Where combine harvesters are use, there is a trend towards using large capacity centralized seed cleaners. These are normally equipped with a series of vibrating sieves and are capable of 10-30 tons per hour.
If grain is to be stored safely for extended periods it must
· have less than 13- 14% moisture,
· be protected from insects and rodents and
· be protected from absorbing moisture either through rain or the surrounding air.
Grain is traditionally stored in 40-50kg sacks, which are made from jute or woven plastic. These bags are stacked under a roof or in a shed and must be periodically fumigated to control insects. Some farmers use granaries, which are made from timber or mud/cement or large woven baskets and these also suffer from insect and rodent damage.
Sealed storage is an option that has a lot of potential in the tropics. If grain is dried to 14% and stored in a sealed storage it reduces the risk of insect and rodent damage and the grain should not absorb moisture from the atmosphere or be damaged by rain. Sealed storages come in all shapes and sizes. They may range from a sealed 200-liter drum to the more complex and costly sealed plastic commercial storages. Most large commercial steel and concrete silos being used in western countries can be sealed for fumigation.
Rice Quality Training Manual
Equilibrium moisture content
In storage, the final moisture content of seed depends on the temperature and relative humidity of the air that surrounds the grain. The final grain moisture content resulting from storage is called the ‘equilibrium moisture content’ or EMC. The following table shows the EMC of paddy under different storage conditions. The underlined & colored areas represent the desirable environmental conditions for storage of paddy for food purposes in the tropics. If grain is not protected against humidity in the air, in particular in the rainy season when the relative humidity may reach 95%-100%, grain moisture content will rise leading to quality deterioration.
It is often said that milling is more an art than a science. Using good quality paddy, in a well-maintained mill, operated by a skilled miller produces high quality head rice. Poor quality paddy will always result in poor quality milled rice irrespective of the type of rice mill and the skill of the miller. Similarly, the use of good milling equipment and good quality paddy will not ensure a high quality product. The best quality milled rice will be attained from a mill that has
· a system of pre cleaning the paddy,
· uses a rubber roller to remove the husk,
· has two separate whiteners and one polisher and
· grades the polished white rice.
Having at least two stages in the whiting process and a separate polisher will reduce over heating the rice during milling and should allow the miller to set the individual machines to give the highest head rice and milling yield. Continual maintenance, monitoring, adjustment and replacement of components such as rubber rollers and sieves is essential to maintain high quality rice.

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Rice Quality Training Manual
4.0 Quality characteristics of milled rice
The quality characteristics of milled rice are classified both physically and chemically.
Physical characteristics

Milling degree. The degree of milling or percent brown rice removed as bran affects the level of recovery and influences consumer acceptance. Apart from the amount of white rice recovered, milling degree influences the color and also the cooking behavior of rice Unmilled brown rice absorbs water poorly and does not cook well. The water absorption rate improves progressively up to about 25% milling degree after which, there is very little effect.
The flow (frictional property) and packing (bulk density) behaviors of rice are also depend on milling Likewise, the nutrient content of rice is also strongly influenced since most micro-nutrient located largely in the peripheral layers of brown rice are removed with high milling degree.
Head rice percentage. The head rice percentage is the volume or weight of head grain or whole kernel in the rice lot. Head rice normally includes broken kernels that are 75-80% of the whole kernel. High head rice yield is one of the most important criteria for measuring milled rice quality. Broken grain has normally only half of the value of head rice. To a large extent, the characteristics of the paddy determine the potential head rice yield although the milling process is responsible for some losses and damage to the grain.
This characteristic is a combination of varietal physical characteristics and the degree of milling. In milling, the whitening and polishing greatly affect the whiteness of the grain. During whitening, the silver skin and the bran layer of the brown rice is removed. Polishing is undertaken after whitening to improve the appearance of the white rice. During polishing some of the bran particles stick to the surface of the rice which polishes and gives a shinier appearance.
Chalkiness. Grain appearance is largely determined by the endosperm opacity and this is commonly classified as the amount of chalkiness. Opaqueness has an overall chalky texture caused by interruption of final filling of the grain. Though chalkiness disappears upon cooking and has no direct effect on cooking and eating qualities, excessive chalkiness downgrades the quality and reduces milling recovery.
Chemical characteristics
Gelatinization temperature. The time required for cooking is determined by gelatinization temperature. Environmental conditions, such as temperature during ripening, influence gelatinization temperature. A high ambient temperature during development results in starch with a higher temperature.
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 (Little et al, 1958). 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.

Alkali spreading value corresponds to gelatinization temperature as follows:
• 1-2 high (74.5-80oc),
• 3, high intermediate,
• 4-5, intermediate (70-74oC), and
• 6-7, low (<70oc).>2% amylose),
• very low (2-9% amylose),
• intermediate (20-25% amylose) and
• high (25-33% amylose).
The colorimetric iodine assay indexes the amylose content of milled rice.
Gel consistency Gel consistency measures the tendency of the cooked rice to harden on cooling. Gel consistency is determined by heating a small quantity of rice in a dilute alkali. This test differentiates the consistency of cold 5.0% milled rice paste. Within the same amylose group, varieties with a softer gel consistency are preferred, and the cooked rice has a higher degree of tenderness.
Harder gel consistency is associated with harder cooked rice and this feature is particularly evident in high-amylose rice. Hard cooked rice also tend to be less sticky.

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Rice Quality Training Manual
3.0 Quality characteristics of paddy or rough rice
A number of interrelated features determine the quality of paddy. These are:
• Moisture content of paddy,
• Purity degree,
• Varietal purity,
• Cracked grains,
• Immature grains,
• Discolored/fermented grains and damaged grains.
These quality characteristics are determined by the environmental weather conditions during production, crop production practices, soil conditions, harvesting, and post harvest practices
Moisture content Moisture content has a marked influence on all aspects of paddy and rice quality and it is essential that paddy be milled at the proper moisture content to obtain the highest head rice yield. Paddy is at its optimum milling potential at moisture content of 14%. Grains with high moisture content are too soft to withstand hulling pressure without undue breakage and may be pulverized. Grain that is too dry becomes brittle and has greater breakage.
Moisture content and temperature during the drying process is also critical as it determines whether fissures and/or full cracks are introduced into the grain structure.
Degree of purity. 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, etc. These impurities generally come from the field or from the drying floor.
Unclean paddy increases the time taken to clean and process the grain. Foreign matter in the grain reduces milling recoveries and the quality of rice and increases the wear and tear on milling machinery.
Variety Purity. A mixture of varieties causes difficulties at milling and usually result in reduced capacity, excessive breakage, lower milled rice recovery and reduced rice Different sizes and shaped grains makes it more difficult to adjust the hullers and polishers to produce whole grains. This results in low initial de-hulling efficiencies, a higher percentage of re-circulated paddy, non-uniform whitening, and lower grade of milled rice.
Grain dimensions. Grain size and shape (length-width ratio) is a very stable varietal property. Long slender grains normally have greater breakage than short, bold grains and consequently have a lower mill rice recovery. The grain dimensions will also dictate to some degree the type of milling equipment needed. As an example, the Japanese designed milling equipment may be better suited to short-bold grains.
Cracked grains. Overexposure of mature paddy to fluctuating temperature and moisture conditions leads to development of fissures and cracks in individual kernel. Cracks in the kernel are the most important factor contributing to rice breakage during milling. This results in reduces milled rice recovery and head rice yields.
Immature grains. The amount of immature paddy grains in a sample has a major affect on head rice yield and quality. The immature rice kernels are very slender and chalky and this results in excessive production of bran, broken grains and brewer’s rice. The optimal stage to harvest grain is at about 20-24% grain moisture or about 30 days after flowering. If the harvest is too late, many grains are lost through shattering or dry out and are cracked during threshing, which causes grain breakage during milling
Damaged grains. Paddy deteriorates through biochemical change in the grain, the development of off-odors and changes in physical appearance. These types of damage are caused from water, insects, and heat exposure.
Yellowing is caused by over-exposure of paddy to wet environmental conditions before it is dried. This results in a combination of microbiological and chemical activity that overheats the grain similar to a milled form of parboiling. These fermented grains frequently possess partly gelatinized starch cells and generally resist the pressures applied during grain milling. While the presence of fermented grain does not affect milling yields it does downgrade the quality of the milled rice because of the unattractive appearance.
The presence of black spots around the germ end of the brown rice kernel is caused by the microorganisms (fungi) and is increased by unfavorable weather conditions. In the process of milling, these black spots are only partly removed which consequently increases the presence of damaged grains.

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Rice Quality Training Manual
2.0 Grain quality characteristics
Rice grain quality represents a summary of the physical and chemical characteristics that may be genetic or acquired properties.
The genetic properties include:

• chemical characteristics (gelatinization temperature, apparent amylase content, gel consistency, alkali spreading value and aroma),
• shape,
• size,
• color of grain,
• chalkiness,
• bulk density,
• thermal conductivity,
• equilibrium moisture content and
• flowability.
The acquired properties or environmental factors are either additional to the normal complement of genetic qualities or are the consequence of certain genetic qualities being lost or modified. The important acquired properties are:

• moisture content,
• grain purity,
• physical and pest damage, cracked grains,
• presence of immature grains and
• milling-related characteristics (milling and head rice recoveries, grain dimensions, whiteness, milling degree and chalkiness) will likewise be included.
Milling-related characteristics are relevant measures of value because these are the major concern of consumers. The quality characteristics of paddy and milled rice can be considered separately.

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Rice Quality Training Manual
1.0 Introduction
Quality is not always easy to define as it depends on the consumer and the intended end use for the grain. All end users want the best quality that they can afford. As countries reach self-sufficiency in rice production, the demand by the consumer for better quality rice has increased. Traditionally, plant breeders concentrated on breeding for high yields and pest resistance. Now the demand is to incorporate preferred quality characteristics that increase the total economic value of rice.
Grain quality is not solely a varietal characteristic but also depends on the crop production environment, harvesting, processing and handling systems. Therefore, maintaining good grain quality is the concern of all disciplines such as breeding, agronomy, entomology, chemistry and engineering. The quality of grain is best when it reaches physiological maturity. Management from that point forward will determine the rate of decline in quality but is unable to stop some decline in quality from occurring.

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Rice Quality Training Manual
Grain Quality

Table of Contents

1. Introduction

2. Grain quality characteristics

3. Quality characteristics of paddy or rough rice

4. Quality characteristics of milled rice

5. Improving or maintaining rice quality

6. Measuring physical properties of paddy
7. Measuring physical properties of milled rice
8. Measurements of chemical characteristics milled rice

9. Practical exercises

10. Appendices

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Rice Quality Training Manual

Time Subject Location
Day 1
Session 1 Introduction Class room
• What is quantity? • Evaluation local rice
• Brainstorming session
Session 2 • Identify and list key parameters to assess grain quality
• Measurement of grain quality • Brainstorming session
• Determine white rice quality
Session 3 • Determine cooking quality
• Economics of grain quality • Evaluation cooked rice
• Brainstorming session
Session 4 • What effects or determines grain quality • Brainstorming session
Summary Discussion
Day 2
Session 5 • What is good seed quality
• Economics of good seed
• Ways of improving seed quality • Brainstorming session
• Determining seed quality
Session 6 • Drying storage of grain and seed • Evaluate post production systems
Session 7 • Plant nutrient requirement
• Leaf color chart
• Plant establishment techniques •
Session 8 Summary and conclusions
Day 3
Session 5 • Improving crop production in farmers fields • Evaluate crop growing conditions
Session 7 • Field Visit: Improving post-production parameters-drying/storage/processing • Evaluate post production systems
Session 8 Summary and conclusions Final discussion

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Rice Quality Training Manual

Purpose This course examines the different factors that affect rice seed and grain quality, explains how to measure quality and outlines ways of improving grain quality.

Rationale As countries reach self-sufficiency in rice production, the demand by the consumer for better quality rice and rice seed has increased. Traditionally, plant breeders concentrated on breeding for high yields and pest resistance. Now the demand is to incorporate preferred quality characteristics that increase the total economic value of rice. Grain quality is not solely a varietal characteristic but also depends on the crop production environment, harvesting, processing and handling systems. Therefore, maintaining good grain quality is the concern of all disciplines such as breeding, agronomy, entomology, chemistry and engineering.

Objectives On completion of this course, participants will be able to:

• Measure grain quality,
• Measure seed quality
• Understand the different factors that effect grain and seed quality and
• Evaluate a rice mill and a storage facility