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The quality and condition of produce sent to market and its subsequent selling price are directly affected by the care taken during harvesting and field handling. Whatever the scale of operations or the resources of labour and equipment available, the planning and carrying out of harvesting operations must observe basic principles.
The objective of the grower should be:
To meet these objectives, success in harvesting and marketing must depend on planning from the earliest stages of production, particularly in regard to:
With small-scale family production for local markets, the labour supply will probably not be a problem. As the scale of commercial production and the distances between the rural producer and urban consumer increase, more exacting requirements will have to be met in regard to training and supervising labour. It is economically sound in terms of return to invest more in proper packing and handling of the produce before it leaves the farm. Growers will have to train their own field labour, accepting whatever support local extension workers are able to provide.
5.4.1 Training workers. This training should cover general aspects of produce-handling for all workers and specific training for those engaged in tasks requiring greater skill.
General training. For everyone concerned with harvesting and field handling, general training should include:
- Wooden containers with rough edges, splinters, protruding nails or staples;
- Overpacking containers which are to be stacked;
- Damaging produce with long fingernails or jewellery;
- Dropping or throwing into containers at a distance;
- Throwing, dropping or rough handling of field containers.
- Placing the produce directly on to the soil, especially wet soil;
- Using dirty harvesting or field containers contaminated with soil, crop residues or decaying produce: containers must be kept clean;
- Contact with oil, gasoline, or any chemicals other than those used specifically for authorized post-harvest treatments.
Specific training. Workers allocated to specialized tasks, such as crop selection and harvesting, and the post-harvest selection, grading and packing (if applicable) of the crop should be given specific training. This will include demonstration and explanation of:
When the crop is ready for harvest, labour and transport are available, and operations organized, the decision as to when to start harvesting will depend largely on:
The flexibility of the marketing date will depend on the crops. Some, such as root crops, can be harvested and sold over a long period, or stored on the farm to await favourable prices. Others, such as soft berry fruits, must be marketed as soon as they are ready or they will spoil.
When the decision to harvest has been made, the best time of day must be considered. The aim is to dispatch the produce to market in the best possible condition, that is, as cool as possible, properly packed and free from damage.
The basic rules to observe are:
Produce for local markets can be harvested early in the morning. For more distant markets it may be an advantage-if suitable transport can be arranged-to harvest in the late afternoon and transport to market at night or early the next morning.
5.6.1. By hand. In developing countries, most produce for internal rural and urban markets is harvested by hand. Larger commercial producers may find a degree of mechanization an advantage, but the use of sophisticated harvesting machinery will be limited for the most part to agro-industrial production of cash crops for processing or export or both. In most circumstances, harvesting by hand, if done properly, will result in less damage to produce than will machine-harvesting.
Hand-harvesting is usual where fruit or other produce is at various stages of maturity within the crop, that is, where there is need for repeated visits to harvest the crop over a period of time. Machine-harvesting is usually viable only when an entire crop is harvested at one time.
Root and tuber crops. Most staple roots and tubers that grow beneath the soil are likely to suffer mechanical injury at harvest because of digging tools, which may be wooden sticks, machetes (or cutlasses, pangas or bolos), hoes or forks.
Harvesting of these crops is easier if they are grown on raised beds or mounds, or "earthed up" as is common in potato-growing. This enables the digging tool to be pushed into the soil under the roots or tubers, which then can be levered upwards, loosening the soil and decreasing the possibility of damage to the crop (Figure 5.1).
Other root crops, such as taro, carrots, turnips, radishes, etc. can be loosened from the soil in a similar manner by inserting the tool into the soil at an angle and levering the roots upwards. This method can also be used for celery if it has been earthed up or buried to blanch the stems.
Figure 5.1 Damage in harvesting roots' tubers and other underground crops is more easily avoided if crops are grown in mounds or raised beds.
Vegetables. Either the whole or a part of vegetative growth can be harvested by hands only or sharp knives. Knives must be kept sharp and clean at all times or they may spread virus diseases from plant to plant. Harvesting methods vary with plant parts harvested:
Flower structures. Immature flower heads (cauliflower, broccoli) can be cut with a sharp knife and trimmed in the field; broccoli can be snapped off by hand and subsequently trimmed;
Mature flowers (squash, chayote, pumpkin): flowers are plucked individually by hand, or whole shoot-bearing flowers are harvested as a vegetable.
Fruits. Many ripe fruits and some immature seed-bearing structures such as legume pods have a natural break-point of the fruit stalk, which can easily be broken at harvest. Fruit and other seed-bearing structures harvested in the immature or unripe green state are more difficult to pick without causing damage to either the produce or the plant. These are best harvested by cutting them from the plant, using clippers, secateurs or sharp knives. The clippers may be mounted on long poles for tree fruits, with a bag attached to the pole to catch the fruit (Figure 5.2).
Plucking methods vary according to the kind of produce being harvested:
5.6.2 Mechanical aids. Because the supply of fresh produce to domestic markets in developing countries comes mainly from relatively small-scale producers with limited resources, mechanical systems for "once over" crop harvesting are likely to be rare. There is scope, however, for the use of mechanical aids in modest commercial operations, especially where tractors are available.
Figure 5.2 Picking poles are used to harvest tree fruit which cannot be reached from the ground or a ladder. Both the factory-made (a) and home-made (b) types have a cutting device and a catching bag (Figure 5.2a is adapted from A manual of post-harvest handling systems for perishable food crops. No. 001 Mango, Ministry of Agriculture. Lands and Food Production. and UCA. Trinidad and Tobago, 1986.)
The jobs where such aids are likely to be of use are:
The packing of produce directly into marketing packages in the field at harvest reduces the damage caused by multiple handling and is used increasingly by commercial growers. It is not a common practice in rural areas, where produce is sent to nearby markets and elaborate packaging cannot be justified, but commercial growers can view it as cost-effective if the packaging takes produce in better condition to market, where it can command a higher price.
Figure 5.3 A natural break-point occurs on many mature fruits at the junction of stem and stalk. At harvest time. thumb pressure applied there should be accompanied by lifting, pulling and turning the fruit
At all stages of harvesting and handling, methods should aim at avoiding damage to produce and providing ventilation to prevent temperature rises.
5.7.1 Selecting field containers for harvesting. These must be of a size that can be conveniently carried by the harvest worker while moving through the field:
When unventilated bulk bins are used in the field, produce should be left in them only briefly, and protected from sun or rain. Produce held in bulk for long will overheat and be more subject to decay. Bulk bins transported over long distances must be perforated to minimize heat build-up in the contents.
5.8.1 Field and farm transport. Routes for the movement of produce within farm fields should be planned before crops are planted. Farm roads should be kept in good condition because great damage can be inflicted on produce carried over rough roads in unsuitable vehicles.
Containers must be loaded on vehicles carefully and stacked in such a way that they cannot shift or collapse, damaging their contents (Figure 8.1). Vehicles need good shock absorbers and low-pressure tyres and must move with care. Jolting of laden containers can aggravate damage to produce on rough roads, even at low vehicle speeds.
5.8.2 Transport from the farm. The destination of the produce leaving the farm will usually be one of the following:
Most fresh produce ready for market is composed of large numbers of small units of similar size which must be moved in amounts conveniently handled by one person. This is best achieved by using containers of capacities from 3 to 25 kg, up to dimensions of about 60 per 40 per 30 cm. Some commodities (e.g. potatoes) may be marketed in 25 or 50 kg sacks, and other large items, such as whole bunches of bananas, are moved without packaging. Leafy vegetables can be sold loose or tied in bundles and not packaged.
Most developing countries use traditional baskets, sacks and trays to carry produce to markets. These are usually of low cost, made from readily available materials such as dried grass, palm leaves or bamboo. They serve the purpose for fresh produce carried over short distances, but they have many disadvantages in big loads carried long distances.
Large commercial quantities of produce need better packaging in order to minimize losses and achieve the most economical use of transport. The aim is to protect the produce from damage in handling, transport and storage and to provide easily handled and counted containers of uniform size.
Packages of standard size can reduce the need for repeated weighing and can facilitate handling, stacking and loading. A wide variety of package types is fabricated from paper and paper products (compressed cardboard and corrugated cardboard, called fibreboard in some areas), wood and wood products (sawn timber and compressed chips) and plastics, both pliable and rigid. Each type must be considered in terms of its utility, cost and capacity to enhance the value of the produce.
Economy in packaging is always a desirable goal. A study in Thailand showed that a plastic crate, while costing five times as much as a traditional bamboo basket of similar capacity, was still useful after 20 times the number of journeys, putting the cost per journey of the plastic crate at about one-quarter of that of the bamboo basket. The crate also provided better protection of produce, easier handling and better stowing, and was easier to clean.
Perhaps improvements in the design and construction of indigenous containers might, in the context of the small-scale grower, prove to be a better solution than buying plastic crates.
6.2.1 From injuries
Cause: sharp objects piercing package; splinters in bamboo or wooden containers; staples or nails protruding in containers;
Effect: deep punctures or cuts in produce, leading to water loss and rapid decay
Cause: throwing or dropping of packages; sudden starting or stopping of vehicle, causing load movement; speeding vehicle on rough road;
Effect: bursting of packaging, bruising of contents
Cause: flimsy or oversized containers; containers overfilled or stacked too high or both; collapse of stacked containers during transport;
Effect: bruising or crushing of contents (Figure 6.1)
Cause: vibration of the vehicle itself and from rough roads;
Effect: wooden boxes come apart, damaging produce
6.2.2 From the environment
Cause: exposure of packages to external heat, e.g. direct sunlight, or storage near heating system; natural buildup of internal heat of produce owing to poor ventilation within package, in storage or vehicle;
Effect: fruit becomes overripe or softens; produce wilts and develops off-flavours; decay develops rapidly; cardboard cartons may become dry and brittle, easily damaged on impact;
Cause: low or subzero ambient temperatures; exposure of sensitive produce to temperatures below chilling or freezing tolerance level during storage;
Effect: damage to chilling-sensitive produce; breakdown of frozen produce on thawing; plastic containers become brittle and may crack;
Cause: exposure to rain or high humidity; condensation on packages and produce moved from cold store to damp atmosphere at ambient temperature; packing wet produce in cardboard containers;
Effect: softening and collapse of stacked cardboard containers; squashing of produce in collapsed containers; decay promoted in damaged produce;
Cause: plastic sacks and crates not treated with an ultraviolet inhibitor eventually break up when exposed to direct sunlight;
Effect: disintegration of plastic sacks damages produce when it is moved; fracturing of plastic crates can cut or bruise produce;
6.2.3 From other causes
Cause: contamination of containers stored near chemicals; damage to produce by containers treated with preservatives, e.g. boxes made from wood treated with pentachlorphenate (PCP) (see colour section, Figure 5); contamination of produce from boxes affected by mould growth;
Effect: flavour contamination or surface damage and discoloration of produce in contact with container; decay of produce owing to contaminating moulds; wood-rotting moulds cause collapse of boxes;
Cause: insects present in packed produce; wood-boring insects in wooden boxes;
Effect: consumer resistance and legal problems from presence of insects (e.g. spiders, cockroaches) in packed produce; spread of wood-destroying insects in infected boxes;
Cause: contamination and eating by rodents and birds; pilfering by humans;
Effect: rejection of damaged produce by buyers or inspectors; loss of income through loss of produce.
The use of packaging represents an added cost in marketing and the price of the marketed product must take account of the capital outlay and unit-packaging cost as well as expected profit. To make an exact assessment of the added value is difficult because many factors may offset the cost of packaging, for example:
It is clear, however, that packaging must not exceed the willingness of the market to accept the added value of the product, i.e. the extra cost involved.
6.3.1 Prevention of injuries to produce. Suitable packages and handling techniques can reduce the amount of damage to which fresh produce is exposed during marketing:
6.3.2 Effect of packaging on other types damage
Packaging in general has poor insulating qualities and will have little effect on preventing damage from heat or cold. Lack of ventilation in packaging delays cooling and may contribute to high-temperature damage arising from heat generated by the produce itself. Recently developed expanded polystyrene packages have good insulating properties and are used, topped with ice, to transport vegetables with high respiration rates.
The availability and cost of such packages make them inappropriate in most developing countries.
High humidity and free water (e.g. rain) quickly weaken cardboard boxes, which get soggy and collapse when wet. This problem can be overcome in manufacture only by waxing the cardboard or by facing it with moisture resistant plastic.
Decay of produce packed in wet sacks or in wet wooden or cardboard boxes will be accelerated.
6.3.3 Chemical contamination. Packaging will not protect produce from contamination by outside sources of chemicals. The containers themselves become impregnated and contribute to the contamination.
Sacks and "knocked down" wooden or cardboard boxes awaiting assembly should not be stored in the same area as chemicals.
Packaging can be a major item of expense in produce marketing, so the selection of suitable containers for commercial-scale marketing requires careful consideration.
Besides providing a uniform-size package to protect the produce, there are other requirements for a container:
6.4.1 Size and shape of packages. Packages should be of a size which can be easily handled and which is appropriate to the particular marketing system. The size should be no larger than is compatible with these requirements, especially with wooden boxes. The ratio of weight of the container to that of the produce it contains is important. Where transport charges are calculated on a weight basis, heavy packaging can contribute significantly to the final cost of the saleable product.
The shape of packages is also significant because of the loading factor: the way the load is positioned on the transport vehicle for maximum capacity and stability. Round baskets, whether cylindrical or tapered, hold considerably less produce than do boxes occupying the same space. A cylindrical basket contains only 78.5 percent by volume compared with a rectangular box occupying the same space.
6.4.2 The need for ventilation in packages. Suitable packaging for any product will consider the need to keep the contents well ventilated to prevent the buildup of heat and carbon dioxide. The ventilation of produce in containers is a requirement at all stages of marketing, but particularly during transport and storage. Ventilation is necessary for each package, but there must also be an adequate air flow through stacked packages. A tight stack pattern is acceptable only if packages are designed to allow air to circulate through each package and throughout the stack. Sacks and net bags must be stacked so that air can circulate through the contents.
The effectiveness of ventilation during transport also depends upon the air passing through the load.
Packaging for fresh produce is of several types:
6.5.1 Natural materials. Baskets and other traditional containers are made from bamboo, rattan, straw, palm leaves, etc. throughout the developing world. Both raw materials and labour costs are normally low, and if the containers are well made, they can be reused.
6.5.2 Wood. Sawn wood is often used to make reusable boxes or crates, but less so recently because of cost. Veneers of various thicknesses are used to make lighter boxes and trays (Figure 6.2). Wooden boxes are rigid and reusable and, if made to a standard size, stack well on trucks.
6.5.3 Cardboard (sometimes called fibreboard). Containers are made from solid or corrugated cardboard. The types closing with either foldover or telescopic (i.e. separate) tops are called boxes or cases. Shallower and opentopped ones are called trays. Boxes are supplied in collapsed fore, (that is, flat) and are set up by the user. The setting-up and closing of boxes requires taping, glueing, stapling or the fixing of interlocking tabs (Figure 6.3).
Cardboard boxes are lightweight and clean, and can readily be printed with publicity and information on contents, amounts and weights. They are available in a wide range of sizes, designs and strengths.
6.5.4 Moulded plastics. Reusable boxes moulded from high-density polythene are widely used for transporting produce in many countries. They can be made to almost any specifications. They are strong, rigid, smooth, easily cleaned and can be made to stack when full of produce and nest when empty in order to conserve space.
Figure 6.3 Fresh produce is carried in a variety of cardboard containers
Despite their cost, however, their capacity for reuse can make them an economical investment. The Thailand study mentioned above showed plastic containers still usable after more than 100 journeys.
6.5.5 Natural and synthetic fibres. Sacks or bags for fresh produce can be made from natural fibres like jute or sisal or from synthetic polypropylene or polyethylene fibres or tapes. "Bags" usually refers to small containers of up to about 5 kg capacity. They may be woven to a close texture or made in net form. Nets usually have a capacity of about 15 kg. Bags or sacks are mostly used for less easily damaged produce such as potatoes and onions, but even these crops should have careful handling to prevent injury.
6.5.6 Paper or plastic film. Paper or plastic film is often used to line packing boxes in order to reduce water loss of the contents or to prevent friction damage.
Paper sacks can have walls of up to six layers of kraft (heavy wrapping) paper. They can have a capacity of about 25 kg and are mostly used for produce of relatively low value. Closure can be done by machine-stitching across the top (recommended only for large-scale crop production) or in the field by twisting wire ties around the top by means of a simple tool (Figure 6.4).
Plastic-film bags or wraps are, because of their low cost, widely used in fruit and vegetable marketing, especially in consumer-size packs. In many developing countries, however, large polythene bags are and should not be used to carry produce, especially to market.
Consumer packs wrapped in plastic are not recommended under tropical conditions except perhaps in stores with refrigerated display cabinets.
Prevention of post-harvest food losses: a pictorial review
Injury infection: stem-end rot is caused by infection of the scar the stalk has been broken away from the fruit
Anthracnose of sweet pepper: the unripe green fruit becomes infected in the field but decay develops only as fruit ripens
Growth cracks: tomato skin hardens when growth stops during a dry period; when growth resumes after rain, the skin cracks
Papaya lumpiness: a deficiency of boron during growth turns the seeds brown and gummy
Chemical damage: fruit packed in softwood boxes treated with pentachlorphenate (P.C.P.) only peaches in contact with box were damaged
Packing-house disorrder: efficiency suffers if work is carried out on the floor
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