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Rice (Oryza sativa L.) is a staple food consumed by over half the world population. The total world production of unmilled rice (paddy) is around 592 million tonnes (Mt) (based on the average production for 2000 and 2001). Ninety percent of this total is grown in developing countries, mostly in Asia, while Latin America and Africa produce 3.8 and 2.8 percent, respectively (FAOSTAT, 2001)

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It is estimated that by 2025, 10 billion people will depend on rice as a main food and demand will reach about 880 Mt. Many Asian countries and international institutions agree to the strengthening of national programmes for policy and financial support to research, seed production and extension of hybrid rice (FAO, 2001). In fact, there has been an expansion of area under high-yielding varieties (HYV), and in 1998 more than 90 percent of irrigated areas in Asia were under HYVs (Evenson, 1998). Methodology on the impact of the improvement of productivity on postharvest operations has been developed by FAO for several crops including rice (Phan, 1998). As HYVs are increasingly used, the post-harvest system must be improved, including infrastructure development and also the dissemination of technologies, allowing small and medium farmers to prevent food losses and consequently to achieve the food security which is a priority of FAO in its fight against hunger

The rice post-harvest system requires improvement in the use of resources for research and development, particularly with regard to the level of post-harvest losses. These losses are attributed to a combination of factors during production and post-production operations (De Padua, 1999)

an overview of rice post-harvest technology: use of small

This paper presents an overview of the main postharvest operations traditionally used by rice farmers in developing countries and the importance of post-harvest technologies for minimizing rice losses. Inadequately performed drying and storage operations contribute to increased losses. The advantages of the household metallic silo are discussed and it is proposed as a feasible and suitable alternative - highly recommended by FAO - for small and medium rice farmers. While this study does not address drying operations in detail, it should be noted that they are complementary to storing

The post-harvest system consists of a set of operations which cover the period from harvest through to consumption. An efficient post-harvest system aims to minimize losses and maintain the quality of the crop until it reaches the final consumer. When food losses are minimized, both food security and income increase, and this is of vital importance for small and medium farmers, particularly in developing countries. From a socio-economic point of view, the implementation of an efficient post-harvest system in any community must provide equitable benefit to all those involved in the system (Grolleaud, 2001)

The traditional concept of post-harvest losses - for the main part quantitative losses - is currently changing. Many post-harvest specialists recognize that measurement of post-harvest losses is a very relative concept for various reasons; for example, losses could be determined as a function of theoretical yield, real yield, soil and fertility conditions, variety etc. Then there are the other losses which are not normally measured, such as agricultural inputs, time, manual labour, lost opportunities etc. In spite of the above, when post-harvest losses are assessed - whether in grains, cereals, fruits or vegetables - the most practical approach (and therefore the norm) continues to be quantitative measurement. To obtain reliable data of post-harvest losses, it is nevertheless important to establish a methodology which takes into account a range of factors (cultivar size, plot size etc.). Data should be supported by basic statistical analysis in order to understand how efficiently a post-harvest system works (Calverley, 1994). Likewise, observations and rapid appraisal in situ by an expert may help to identify how efficiently a post-harvest operation system works within a rural community and for a specific crop

The post-harvest system for rice deserves special attention: rice is a major staple food in the world and is mostly produced in developing countries where the implementation of post-harvest technologies is urgent in order to prevent food rice losses. It has been estimated that rice post-harvest losses may be as high as 16 percent. A study carried out in China revealed that total post-harvest losses ranged from 8 to 26 percent, with storage and drying the most critical operations (Ren-Yong et al., 1990)

an overview of rice post-harvest technology: use of small

The quantity and quality of final milled rice depend on the efficiency of farming management, field operations and post-harvest operations. Decisions are taken from planting through to consumption of the rice crop. Initial decisions about the variety to be planted determine intrinsically desirable characteristics and depend upon consumer preference as well as the technical capacity of the farmers during production and post-production operations. These characteristics in turn become factors which influence efficiency, grain loss magnitude, choice of harvesting and threshing technology, rate and quality of the drying and dehusking process, and eventually total recovery of the milled rice. Then there are the wrong practices at the planting stage which can lead to losses: planting of red rice admixture, attacks by rodents and birds, poor weeding and a harvest maturity date which can be too early or too late

It is important to point out that the differences in varieties planted in certain localities also affect the final milled rice, as the high-value rice market usually prefers a pure and single variety. Nevertheless, for reasons of biodiversity and more sustainable agriculture, planting different varieties (although not necessarily in the same field) is an excellent strategy for improved food security. Sometimes, high management is required to monitor planting in order to prevent varieties becoming mixed; on the other hand, varieties are sometimes deliberately mixed to produce special characteristics, such as consistency of flavour, which cannot be found in a pure variety

During pre-harvest operations, efficient technology and input management, as well as timeliness of activities, are important, and this applies also to postharvest operations for good yield and quality and in order to obtain good prices for the milled rice and byproducts. Correct timing at harvest is essential to avoid losses incurred by harvesting too soon or too late. Immature grains harvested too early result in a high percentage of brokens and low milling recovery, while if harvesting is delayed, the crop is exposed to insects, rodents and birds, in addition to the risks of lodging and shattering. The optimum harvest time should be chosen depending on the variety planted (Lantin, 1997)

an overview of rice post-harvest technology: use of small

Harvesting includes numerous operations, including: cutting the rice stalk; reaping the panicles; laying out the paddy-on-stalk or stacking it to dry; and bundling for transport. Correct harvesting and handling operations can considerably reduce post-production losses. Excessive handling creates problems in terms of both quality and quantity

The sequence of manual harvesting, field drying, bundling and stacking in traditional systems can cause losses of between 2 and 7 percent (Toquero and Duff, 1974). At this stage, losses can occur when secondary tiller panicles are missed when the sickle cuts 60 cm above ground in lowland rice. Also, delayed harvest causes shattering losses during harvesting and transport

This is accomplished by using a hand-held cutting tool (Yatab in the Philippines, Ani-ani in Indonesia, Kae in Thailand, Espigadora in Bolivia). The method is used in areas where traditional varieties are resistant to shattering. Resistance to shattering is particularly important during handling and when transporting the bundles of panicles from field to house. The labour time required for this method is 240 labour-hours/ha (done mostly by women and older children), which is four times that required with the hand-sickle method. It remains popular because of the social custom of chatting while working. In addition, it generates income among the landless rural population and is suitable for hilly and terraced areas

an overview of rice post-harvest technology: use of small

This is a widely used manual method presenting different styles in the design. It requires between 80 and 180 labour-hours/ha. The stalk is cut about 10 to 15 cm above the ground or with a stalk length of about 60 to 70 cm for easy bundling and threshing. Reaping efficiency depends on various cultural practices, plant density and variety, degree of lodging, soil conditions and the skill of the harvester. Lodged paddy and saturated soils may considerably reduce the cutting rate

These methods are generally used when labour is scarce; otherwise, harvesting is generally still done with a sickle in most developing countries. The use of mechanized harvesting methods in some areas depends upon the custom and suitability of the machine and other socio-economic factors. Some examples of these machines are:

Combine: very popular, its adoption in Japan, Korea and other Asian countries is slow only because of its high cost. The binder can harvest 0.05 ha/hour. A similar, large model was developed in Thailand to resolve the problems of scarcity and cost of labour; Viet Nam may also adopt mechanized methods because of economies of scale. Some other Asian countries import second-hand, large combines for harvesting the basic rice crop. In commercial rice production, large combines are generally used in countries such as Brazil and Uruguay in Latin America, in Europe and in the United States of America. In Africa, on the other hand, these machines (introduced through international aid programmes) have had little impact because of the lack of maintenance facilities

an overview of rice post-harvest technology: use of small

Stripper harvester: an innovation from IRRI and an adaptation of the rotary stripping combine principle developed by Silsoe Research Institute in the United Kingdom, it works with varieties which are non-lodging, medium height, with erect panicles and low to medium shattering (Naphire, 1997)

There continue to be constraints for farmers in developing countries to the adoption of mechanical harvesting methods: low income, reluctance to move away from traditional methods, poor mechanical aptitude, the desire to save straw for off-farm uses, lack of access to the field, excessive moisture content, uneven ripening etc. Other limiting factors are the high cost of imported equipment and the fact that machinery management must be competitive with the relatively low cost of labour (IRRI, 1997)

In developing countries, transportation of paddy from the field to processing areas is performed mainly by humans and animals, and sometimes using mechanical power. In hilly areas where paddy fields are terraced (e.g. Bhutan, Nepal, some parts of the Philippines and Indonesia) the paddy is transported in panicles or bundles of long stalks using human or animal power. These traditional methods of transport, which are related to the harvesting and field drying activities, very often result in high grain losses. Small and family-sized volumes of paddy are generally transported in bags from the house storage to the small rice mill on foot, in bullock carts, by bicycle, using small vehicles or with public transport - whatever means is available and affordable. Other methods of transport include donkey, buffalo and even boat

an overview of rice post-harvest technology: use of small

In some places, the practice is to windrow the cut paddy in the field to dry for 3 to 7 days, depending upon the weather conditions. Losses are even greater, especially if harvesting is delayed with respect to the crop maturity date. In addition to the losses incurred in cutting, wind-rowing, sun-drying, collecting and bundling of the cut crop, there are those when the bundled paddy-in-straw is loaded onto the person’s back to be carried to the house

Grain then falls en route, especially with the transportation of shattering varieties, and also when the carrier (usually a woman) stops to rest. Nevertheless, some farmers prefer this method for both cultural and practical reasons, as the straw can be used as animal feed

The large losses incurred are the principal drawback to manual transport. Threshing of the paddy in the field and transportation in bags (40-75 kg) can minimize grain losses, however. Sun-drying of the paddy can also be done in the yard of the house rather than on stalks in the field. The normal practice in Asia is to bring the paddy from the field to the roadside manually or using animal power; it is then transported to the drying area or rice mill by motor vehicle (e.g. tricycle, power tiller with trailer, tractor with trailer, truck or lorry). The loading and unloading of the bags require additional labour costs, and these are normally assumed by the buyer

an overview of rice post-harvest technology: use of small

In developing countries and advanced developing countries, the paddy is harvested by combine and is handled and transported in bulk. The paddy is unloaded from the combine by an auger conveyor and loaded into a waiting lorry or tractor-trailer located on the field road (part of the infrastructure for mechanized rice production). The paddy is then unloaded from the lorry or trailer onto a floor hopper in the rice mill area to be conveyed to a mechanical dryer. Finally, commercial rice is bagged at the rice mill and normally transported to wholesale and retail markets by means of vehicles. This mechanized procedure results in much lower losses (Lantin, 1997)

During threshing the paddy kernel is detached from the panicle, an operation which can be carried out either by “rubbing”, “impact” or “stripping”. Rubbing may be done with trampling by humans, animals, trucks or tractor; however, the grain becomes damaged. Mechanical threshers adopt mainly the impact principle, but there is also a built-in stripping action

With a paddy thresher, the unthreshed paddy may be either held or thrown in. In the “hold-on” type, the paddy is held still in the cylinder while spikes or wire loops perform impact threshing. In a “throw-in” machine, whole paddy stalks are fed into the machine and a major portion of the grain is threshed by the initial impact caused by bars or spikes on the cylinder

an overview of rice post-harvest technology: use of small

In a conventional threshing cylinder, stripping may also be used for paddy threshing; impulsive stripping normally occurs with impact threshing. In a throw-in thresher, large amounts of straw pass through the machine and some designs use straw walkers to initially separate the loose grain from the bulk of the straw and chaff (Lantin, 1997)

IRRI developed the Votex Ricefan thresher. A portable machine, as well as being suitable for both paddy panicles and paddy stalks, it may be adapted for wheat, corn, soybean and beans. The Votex Ricefan thresher has been widely accepted among Bolivian paddy farmers (Terán, 1996) and may be either manually or power-operated

Manual threshing is pedal-operated and involves: treading; beating the panicles on a tub, threshing board or rack; or beating the panicles with a stick or flail device. The thresher consists of a rotating drum with wire loops which strip the grain from the panicle when the paddy is fed by hand. This equipment is portable, can be used in hilly areas and is easily operated by women

an overview of rice post-harvest technology: use of small

Paddy as a living biological material absorbs and gives off moisture depending on: paddy moisture content, relative humidity of the air and temperature of the surrounding atmosphere. The respiration of the paddy is manifested in various ways: decrease in dry matter weight; utilization of oxygen; evolution of carbon dioxide; and the release of energy in the form of heat. However, respiration is negligible when the moisture content is between 12 and 14 percent

By and large, paddy is harvested with moisture content of 24 to 26 percent (higher in the rainy season and lower in the dry season). It has a high respiration rate and is susceptible to attacks by micro-organisms, insects and other pests. The heat released during the respiration process is retained in the grain and in the bulk due to the insulating effect of the rice husk, resulting in losses in terms of both quantity and quality. Therefore, harvested grain with high moisture content must be dried within 24 hours: to 14 percent for safe storage and milling, or at most 18 percent for temporary storage of 2 weeks when it is not possible to dry any faster. Delayed drying may result in non-enzymatic browning (stack-burning), microbial growth and mycotoxin production in parboiled rice (NRI, 1991)

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