8. Post-harvest handling

POST-PRODUCTION ADVICE

This guide does not attempt to cover in depth the technical details of post-harvest handling of horticultural crops. FAO and others have covered this in many other publications.^[2] The main emphasis here is on the commercial implications of different harvest and post-harvest practices. The key issues are:

• maintaining quality;

• maximizing shelf life^[3];

• supplying produce when and as the market demands it.

The main way that you can help improve post-harvest handling is by training farmers, both through practical training and by presentations. In the following pages the main ways in which post-harvest techniques can increase farmers' profits are set out.

Harvesting

The timing, techniques and conditions of harvesting can significantly affect prices.

Harvesting and prices. Harvesting early in the season can be carried out to take advantage of opportunities for high prices, e.g. cabbage harvested as spring greens, young carrots sold in bunches, green plums and new potatoes. Taking advantage of these short-term market opportunities requires close links with the market.

Harvesting and crop maturity. The shelf life of the crop and its suitability for long-term storage is affected by the maturity of the crop at harvest. The optimum harvesting stage for most crops depends not only on the climate and distance to the market but also on the variety and the growing conditions. When distant markets are being investigated, experiments should be carried out to find the best maturity to harvest fruits. Send samples at different degrees of ripeness and assess which gives the best results. It may be necessary to call in expert assistance to identify whether long-term crop storage could significantly improve farmer incomes.

Harvesting and quality. Growers often do not understand the effect of their harvesting and handling on the quality of the produce when it reaches the market. Once a fruit is plucked from a plant, or a root or leaf vegetable is harvested, it is cut off from its source of food and, particularly, water. The effects of poor treatment normally show themselves some days later, when the produce is being presented for sale or is in storage. This can often result in disputes, because farmers have sent to market what they consider to be good quality products but by the time these arrive at the market the trader sees produce that has deteriorated badly. An example of this comes from Tonga, in the South Pacific, which used to export capsicum (green pepper) to New Zealand. When the fruit left Tonga they appeared to be in excellent condition but after four days in a ship they arrived in very poor condition. The problem was traced to the use of dirty knives for harvesting.

Poor post-harvest handling leading to low quality produce has two effects; firstly the price is reduced and, secondly, the reputation of the production area is, over time, diminished (again tending to result in lower prices). Improved harvesting and handling of produce will result in a product with better appearance and shelf life and thus better prices.

Time of day for harvesting. Ideally, harvesting should take place when the crop and the climate are coolest and the plant has the highest moisture content. This is in the early morning but other issues have to be taken into account. For example, labour and transport may not be available early in the morning. If transport is a problem the harvest should be rescheduled to avoid produce being left standing in the field for too long. Specific crops often have ideal harvest times. For example, citrus should not be picked until the dew is dry. The best time for harvesting mangoes is mid-morning, when the latex flow is at a minimum.

Field containers. Bags or baskets attached to the waist of the picker enable both hands to remain free. The crop damage associated with moving sacks of produce through the field is thus reduced. When using bags it is preferable to be able to release the bottom so that the produce can be let out gently, rather than up-ending the bag. Containers must be emptied carefully to minimize drop heights and fruit-to-fruit damage. Containers should be cleaned as often as possible.

Using baskets or boxes with sharp or rough edges should either be avoided or the containers should be lined with paper or leaves. Damage is often caused by transferring produce from one container to another. If possible, produce should be harvested directly into the container in which it will be stored and/or transported.

Drying and curing

Drying is used mainly on bulbs in order to extend shelf and storage life. Crops such as onions and garlic can be dried in the field over about six days, by being spread in a single layer. Alternatively, drying can take place under cover in stacked, shallow trays. The aim is to harden the outer scales and remove moisture from the neck of the bulb, in order to extend storage and marketing life.

Most root crops respond to warm, moist conditions after harvest by thickening and hardening their skins. This provides protection against dehydration and infection. Wound healing occurs. This is called curing and it significantly improves storage life of products like potatoes and carrots.

Grading

Grading is carried out so that:

• disease-free and blemish-free produce can be selected for long-term storage;

• top-quality produce can be selected for transport to distant markets;

• produce can be separated according to quality, ripeness, colour and size. Separated produce is packed into different containers to facilitate marketing to consumers with differing quality requirements.

Grading is sometimes carried out on the ground under the shade of a tree. This is both unhygienic and inefficient. Specialist grading areas or sheds are generally open-sided with tin or, preferably, thatched roofs to provide shade. Standing or sitting at tables enables people to grade quickly. Tables covered with polythene sheeting are easy to clean and the sheeting can be replaced cheaply. Lighting should be good. Tin roofs can be painted white to reflect heat, while water trickling down the outside of a shed helps reduce the heat inside the building.

Packaging

Good packaging design enhances the attractiveness of produce, enables it to be handled and marketed in convenient units, and helps to prevent mechanical damage.

Mechanical damage. The four main types of mechanical damage are cuts, compression bruises, impact damage and vibration rubbing.

• Cuts. Care in harvesting and handling will help eliminate cuts and wounds. Lining of packaging with paper or leaves can also prevent damage to the contents.

• Compression bruises. These can be reduced by using containers that are strong enough to withstand multiple stacking. The packaging materials need to be particularly strong at the vertical corners. The packaging should also be shallow enough to prevent the bottom layers of produce from being damaged by the weight of produce above. Cartons must not be overfilled or damage will be caused by the full weight of the pile of produce pushing down on the top layer of fruit or vegetables, causing the weight to be transmitted to the lower layers.

• Impact damage. Shocks in transport or dropping of containers can result in this kind of damage. Dropping may occur either because a package is small enough to be thrown or because it is too big to be easily handled. A packing unit should not exceed 50 kg as this is the maximum weight that can be easily handled. Package size specifications usually depend on the customers' requirements, although in many countries the supply of good packaging materials is limited and buyers may have to accept what is available.

• Vibration rubbing. This kind of damage generally occurs during transport. It can be significantly reduced by preventing the produce from moving within the packaging while, at the same time, ensuring that fruits or vegetables are not forced together. Fruits can be prevented from rubbing against one another by the use of cellular trays, individual wraps or cushioning pads. An example is the use of paper and straw to separate layers of apples. An alternative approach is for the container to be gently shaken, in order to settle the produce, with the space created then being filled.

Packaging materials. Packaging can be the single most expensive cost, as the calculation in Table 6 showed, particularly with non-returnable containers made of wood or cardboard. The benefits of packaging must clearly justify the investment. An example of such a calculation is given in Figure 13. Traders usually aim to minimize costs and are reluctant to invest in packaging unless the financial benefits are clear.

Figure 13
A cost-benefit analysis of packaging

Five types of packaging materials are listed below.

• Locally available natural materials (e.g. wooden boxes or trays, baskets woven from bamboo or willow or cartons made from thin strips of wood or rushes). While use of local materials is normally recommended, overuse can have negative consequences for the environment. In northern India, for example, there have been problems of deforestation because of the use of trees for wooden boxes for apples.

• Fibreboard/corrugated cardboard are increasingly being used, particularly in developed countries.

• Plastic crates are expensive and generally have to be imported. They have the advantage of being re-usable but a system needs to be in place for the containers to be returned to the farms to be refilled.

• Bags and nets are cheap but provide no protection from damage. They are used to package onions, garlic, cabbages and potatoes.

• Plastic and paper are often used as lining or wrapping for produce.

Packaging presentation. Attractive printing and brand names can add value to fresh produce but only in markets where consumers are wealthy and appreciate aesthetics and image. In the produce markets of the Arabian Gulf and Southeast Asia multi-coloured printing is common because it helps to sell the produce and lift prices.

Storage

Produce can be stored for both short-term and long-term purposes. Short-term storage is mainly used to provide flexibility in marketing (e.g. when awaiting transport), or because buyers are not immediately available. Most horticultural crops are perishable and can only be stored for a few days. Only rarely is it worthwhile storing perishable crops to await higher prices, as storage will reduce quality and shelf life whilst adding to costs. Storage is costly and, in most instances, when the produce is withdrawn from storage it has to compete in the market against much fresher produce.

A few crops are adapted for long-term storage. These can be held in store well beyond the normal harvesting period. When they are eventually sold higher prices can usually be obtained and, by extending the marketing season, a larger volume of produce can be marketed. Often, the most successful stores are located in urban areas because:

• produce can be released rapidly onto the market when prices increase;

• refrigerated facilities in urban areas can also be used for a variety of products (e.g. apples in the winter, citrus in the summer, butter and other milk products).

It is rarely worth storing perishable crops to wait for higher prices.

When produce is taken out of store it has to compete with fresh fruits or vegetables.

Refrigerated storage is expensive and can only be justified if it can be run profitably. This requires an adequate demand for storage, good management and a reliable supply of electricity.

Shelf life can, however, be extended without investment in expensive storage equipment. The first priorities should be selecting high-quality produce (i.e. free of bruises, pest and disease damage), maintaining a high humidity and keeping produce in the shade.

In the right conditions, with good management, ventilated stores can be extremely cost-effective, especially for potatoes and onions. Ideally they require cool temperatures at night.

Improving farmers' returns

Emphasis has been given here to improved handling, grading and packaging. Improved prices can result from the quality of an individual consignment. In the longer term, groups of farmers can obtain premium prices by establishing an identity and a reputation as consistently high-quality suppliers by:

• applying minimum grading specifications for a top-quality product;

• grading to this standard;

• agreeing on a name, symbol or 'brand' image, which can be printed on the packaging;

• agreeing that they will only send high-quality produce under the brand name;

• requiring all growers to mark branded packages with their own identification marks so that any produce which is below specification can be traced back to the culprit.

There are many examples of production areas that obtain premium prices because of their reputation for supplying quality produce, but it is important to remember that a reputation that takes years to establish can be quickly destroyed by one or two poor consignments.