This unit outlines some of the post-harvest handling practices that can be used by small-scale or low input Growers, Packers, Shippers, and Marketers of fruit and vegetable crops.

There are two main objectives for applying post-harvest technology:

  1. To maintain quality including appearance, texture, flavour, nutritive value, and food safety.

  2. To reduce losses between harvest and consumption.

Post-harvest handling systems involve many interacting steps, produce is generally handled by many people before arriving at the end consumer. A general series of handling steps will be followed in this presentation each practice will be briefly described.

  • Harvest and Preparation for Market

  • Curing

  • Packinghouse Operations

  • Decay and Insect control

  • Temperature and RH control

  • Storage

  • Transportation

  • Handling at destination

Application of these practices can help small-scale handlers maintain the quality of fruits and vegetables while reducing handling and marketing losses. Fresh produce must be carefully harvested at their correct maturity stages. Use clean smooth harvest containers, provide shade for filled field containers and cool products as soon after harvest as possible.

Harvesting practices should cause as little mechanical damage as possible. Digging gently, using sharp knives & clippers, picking and handling carefully will lessen the damage.

Pickers should wear cotton gloves or remove rings and trim fingernails to avoid damaging the commodities they handle. For some crops, a natural breakpoint forms at the junction of the stem and the stock.

Plastic containers are relatively expensive but durable, reusable, and easy to clean. The containers can be lined with a sheet of foam to help reduce injury to delicate commodities such as asparagus and soft fruits during transport to the packing house.

Field packing reduces the amount of handling of a crop between harvest and consumption. When head lettuce is field packed some wrapper leaves are left on the head to help cushion it during subsequent handling. A small cart helps reduce the bending and lifting by a picker during harvest, while also providing for packed boxes of product.

Root crops like sweet potatoes should be cured if they are to be stored for any length of time before marketing.

Curing

Curing requires high temperature and high relative humidity conditions for a short time. Curing heals harvesting wounds by providing a new protective layer of cells. Yams and other tropical crops can be cured outdoors by piling them in a partially shaded area straw can be used as an insulating material the pile should be covered with canvas or burlap and left for about 4 days.

Best Conditions for Curing

CommodityTemp °CTemp °FRelative HumidityDaysPotato15-2059-6890-955-10Sweet Potato30-3286-9085-904-7Yams32-4090-10490-1001-4Cassava30-4086-10490-952-5

Under controlled temperature and humidity conditions, curing is faster and more uniform, when curing with heated air inside a storage facility, bottom-to-top forced airflow results in the most uniform distribution of heat.

Wetting the floor helps to increase the relative humidity in a curing chamber but if it exceeds 95% it may increase the spread of decay.

The curing of onions, garlic, and flower bulbs refers to the practice of allowing the external layers of skin and neck tissue to dry out prior to handling and storage. These crops can be cured outdoors in windrows or in sacks stacked in rows. The cut foliage of the plants can be used to provide shade during the curing process.

Onions, garlic, and flower bulbs are also cured in temperature and humidity-controlled chambers. Curing with forced heated air is sometimes used in regions where the ambient relative humidity is too high for successful natural drying. If the heaters are located near the ceiling fans are then used to help move the heat downward into the produce.

Packinghouse operations typically include:

  • Dumping

  • Cleaning

  • Waxing

  • Sorting

  • Sizing

  • Packaging

All packing house operations should be covered to limit product warming, protect produce from rain or hail, and provide more comfortable working conditions for workers. Shade can be provided by using a simple canvas or plastic mesh sheet hung from temporary poles or operations that can be located inside a permanent roof structure.

During packing careful sorting is required to remove decayed, injured, immature or over mature produce. Eliminating decayed produce will limit the spread of disease, removing injured, immature or over mature produce saves energy since colds will not be cooled or handled further.

Commodities may need to be cleaned by washing or dry brushing, washing may be desirable for some crops especially root crops such as ginger that often require being immersed in a water bath then sprayed to remove any soil and debris.

Sanitation

Sanitation is essential during washing, using a wash solution containing 100 parts per million of chlorine will help to control the build-up of pathogens during packing operations.

Hypochlorite powder or liquid is inexpensive and widely available. Installing a demand system is useful for maintaining the proper chlorine level in packinghouse wash water. Small-scale packers should test the level of chlorine several times daily using a simple test kit.

Produce should be sorted into quality grades before packing, sorting maybe by maturity, size, or colour.

Packing and Packaging Materials

Horticultural products are generally packed for ease of handling. Waxed cartons, wooden crates or plastic containers are preferable to sacks or open baskets.

While these containers are initially more expensive they can stand up to the high relative humidity found in storage rooms and protect fresh produce from damage when stacked.

Rigid plastic containers are easily cleaned, they can be reused many times. For best handling results containers should be properly filled neither too loose nor too tight. If containers are only partially filled, vibrating produce causes abrasions or bruising to the neighbouring units during transport.

If containers are packed to full compression damage results when containers are closed and stacked. One recommended method for reducing damage is to fill the container spaces with shredded newspaper, it's an inexpensive and lightweight filler.

A wooden log is a typical container for table grapes, this container is very sturdy and maintains a stacking strength during long periods of time at high humidity storage. Often a paper liner is folded over the grapes before the top of the log is nailed in place to protect them from dust and water condensation.

Fibreboard boxes can be manufactured in many sizes and shapes. Containers must be vented with approximately 5% of the surface area of each side open for proper air circulation to occur. If used for forced air cooling the site vents must align when containers are stacked squarely on top of one another corner to corner.

Adding a fibreboard divider to a carton, increases stacking strength. The use of dividers is common with heavy products like Melons.

When locally-made containers have sharp edges or rough inner surfaces a simple, inexpensive liner made from fibreboard protects the fresh produce from damage during handling. Handling packages as unit loads can reduce the work associated with post-harvest handling, stripe and corner boards help stabilise the load.

Modified atmosphere packaging is used with Strawberries and Bush berries. A single pallet load of berries is sealed within a shroud of 5 millimetre polyethylene sheeting on a pallet base covered with a plastic sheet.

enough carbon dioxide is injected via a small hose into the bag to create the 15% level which is effective or decay control.

Hot and Cold treatments

Good management during production is essential to reduce post-harvest disease and insect infestation. Careful harvesting and sorting out damaged or decayed produce before packing and limiting the spread of disease.

Storage at the lowest safe temperature will slow the growth of most fungi and bacteria. In addition to low-temperature storage, there are several post-harvest treatments available to help prevent losses caused by pathogens or insects.

Hot water dips can reduce the number of fungal spores on crops such as lemons, melons, plums, peaches, papaya, sweet potatoes, and tomatoes. hot water dips are especially helpful in controlling subsurface fungal infections. Cold treatments are another option for our controlling insects on commodities that tolerate low-temperature storage. For instance, storing produce for 14 days at 1.7 degrees Celsius (35 degrees Fahrenheit) or 10 days at zero degrees Celsius (32 degrees Fahrenheit) controls fruit flies and other insects on apples, pears, grapefruits, kiwifruit, and persimmon or produce pack before cold storage treatment package vents should be screened to prevent reinfestation by insects during handling.

Sodium or Potassium Bisulfate is used in a sawdust mixture for control of moulds on grapes; the mixture is usually enclosed within a pad that is placed inside a container of grapes. On occasions when fungicides must be applied to produce a tray with holes punched into the bottom can be used to hold the commodity while it's sprayed. For example, Bananas are treated with a fungicide solution using a handheld knapsack sprayer to the point of runoff. The bananas will then dry in a perforated tray before handling. Fungicides must contact a product's entire surface for maximum effectiveness.

Temperature Control

Proper temperature management is the most important individual factor in maintaining product quality. Keeping a product at its lowest safe temperature during handling, storage and transport will increase the post-harvest life because of lowering respiration rate, reducing water loss, decreasing ethylene production/ sensitivity slowing ripening, and limiting the growth of decay-causing organisms.

Several simple practices will enhance cooling. Harvesting early in the morning when products are coolest will reduce the amount of heat that must be removed from harvested crops, shading the product keeps it cool, shading all buildings used for packing house operations, cooling storage, and loading transport vehicles also keep the product cool.

Insulating cooling & storage rooms and loading areas and painting buildings white or silver further reduce interior heat gain. Cooling involves transferring heat from a product to a source of refrigeration either mechanical or ice. Produce should be stacked in cold rooms and patterns that allow plenty of air circulation around the product. Room cooling provides the slowest cooling rate and is too slow for more perishable products. The rate of cooling can be increased by installing a ceiling plenum with cone-shaped Jets through which air is directed down over stored produce.

Forced Air Cooling

Forced air cooling pulls cold moist air through stacks of storage containers and thus it greatly speeds the rate of cooling for any type of produce. If the cost of a fixed unit is too expensive for your operation, a portable forced-air cooler can be constructed using a canvas or a thick polyethylene sheet.

Hydro Cooling

Hydro cooling uses cold water to cool products. Water temperatures should be maintained at the lowest safe temperature for the products being cooled. Products are either showered with cold water or immersed in cold water in batches. Thorough daily cleaning of hydro coolers is necessary to prevent a harmful buildup of decay-causing organisms. Hydro cooling water should be adequately chlorinated to help control decay.

Evaporative Cooling

Evaporative cooling can cool products to slightly above the wet-bulb temperature of the ambient air. Some evaporative cooling can be achieved by wetting products and allowing the surface water to evaporate. Evaporative cooling is particularly useful for cooling chilling sensitive products in warm dry areas. Forced air cooling with evaporatively cooled air provides even more effective cooling the water can be collected and recirculated as needed.

Night Air Ventilation

Night air ventilation is used for cooling both products in areas where nighttime temperatures are substantially lower than produce temperatures. The storage facility should be well insulated and vents should be located at ground level. Vents can be opened at night and closed early in the morning, care should be taken to avoid overcooling or freezing if night air ventilation is used in very cold regions.

Package Icing

Package icing is the process of placing ice around or on top of the product inside a package. Icing can be used only with products that tolerate contact with ice such as carrots, broccoli, radishes, beets, sweet corn, and green onions.

Packaged icing provides fast initial product cooling but the rate slows down after the ice in contact with a product has melted. Some disadvantages of icing include; A 50 to 100 percent increase in package weight and the higher cost of water-tolerant container use.

Top Icing

Top icing generally refers to covering a load of fresh produce with finely crushed ice inside a refrigerated truck. When using this cooling method it's important not to block air circulation inside the transport vehicle. Most products of tropical or subtropical origin are susceptible to chilling injury which occurs at low but above freezing temperatures. Handle chilling sensitive commodities such as capsicum, citrus, melons, and tomatoes at above chilling temperatures to avoid injury.

Chilling injury reduces the quality of the product and shortens shelf-life, you'll recognise the symptoms of chilling injury by for example the dull surface colour of bananas and a lack of ripening of tomatoes.

Humidity Control

Maintaining a high relative humidity in the storage environment helps control the rate of water loss from stored produce. Loss of water causes a loss of quality such as wilting or shrivelling, texture, and increased sensitivity to decay.

Relative humidity can be increased by adding water vapour to the air surrounding the commodity, decreasing product temperature, using waxed cartons, or by adding vapour barriers such as polyethylene liners in boxes.

Storage

Only high-quality products free of damaged or diseased units should be stored. Storage containers must be clean, adequately ventilated, and strong enough to withstand stacking during storage. Commodities stored together must be capable of tolerating a common temperature, relative humidity, and level of ethylene. Storage facilities should be thoroughly clean prior to storage and be kept clean.

Inspection

produce should be inspected regularly for signs of decay, water loss, warming, or chilling. These practices will help to maintain product quality and reduce losses by minimising the buildup of pests and discouraging the spread of diseases.

Storage facilities should be protected from rodents by keeping the immediate area outside the building clean and free from weeds and trash. Rat guards for raised storage buildings can be constructed from tin sheeting. Concrete floors, screens on windows, drains, and vents will help prevent rodent entry.

Waterproof sheets or wooden pallets placed on a floor beneath sacks or cartons of produce help prevent dampness from reaching produce. Waterproof sheets reduce the chance of fungal infection while wooden pallets improve air circulation under the produce.

Insulation

Any type of building used for the storage of horticultural crops should be insulated for maximum effectiveness. An insulated building will require less energy for cooling and maintaining desired temperatures if the structure is cooled evaporatively or by using night air ventilation, a well-insulated building will stay cold longer.

Bulk Storage

When loading potatoes into bulk storage, distribute the fresh produce evenly for proper ventilation uneven loads will result in poor air movement and result in higher storage losses.

Transportation

When transporting bulk loads produce should always be carefully loaded to reduce mechanical damage. Vehicles should be well padded or lined with a protective liner, while other loads should never be placed on top of the bulk commodity.

Maintaining product temperatures and open loads during transport is desirable whenever possible. The condition of the inside of a refrigerated vehicle affects the vehicle's ability to maintain desired temperatures during transport. Trailers should be precooled before loading, handlers should inspect the trailer before loading and check for the

following features:

  • Air delivery chute attached

  • Door seals intact

  • Doors, Floors, and Walls clean and undamaged

  • Floor drains open

  • Inside height and width adequate for the load

  • Load bars available for bracing.

When transporting cartons or sacks of produce, care should be taken to load the containers so that there’s plenty of room for air to circulate throughout the load. Keep the load away from the sides and up off the floor of the vehicle to reduce heat transfer between the product and the warmer or colder trailer surfaces.

Always leave a void between the last stack of fresh produce and the back of the transportation vehicle. The load should be braced using wooden load bars to prevent shifting against the rear doors. This bracing technique will prevent the load from falling against the doors where it will block air circulation, it will also protect workers who open the doors at a destination market.

Some fresh produce may require:

  • Washing

  • Trimming

  • Bunching

  • Sorting

at the wholesale or retail market level. The layout of the workstation used for handling produce should be organised to minimise non-productive movement

Ripening Rooms

Produce such as Bananas and Avocados are often ripened before sold to consumers. Ripening rooms typically operate at temperatures of 59 to 70 degrees Fahrenheit or 15 to 21 degrees Celsius, with Ethylene gas at about 100 parts per million added to the room greatly increases the rate of ripening.

Citrus Degreening

Oranges and Mandarins are often degreened in rooms containing up to 10 parts per million ethylene. Pallet bins should be vented to allow airflow, the greening will shorten the shelf life of Oranges and Mandarins so handlers should carefully consider whether their market demands this optional post-harvest treatment.

Retail displays

Retail markets display horticultural crops in single or double layers to protect the commodities from compression damage and excessive handling by consumers. Temperatures of display tables or refrigerated display bins should be suited to the commodity being sold. For example, while capsicum and tomatoes look pleasing when displayed with lettuce, capsicum and tomatoes are chilling sensitive while lettuce is not.

Sensitivity to Chilling

LowModerateHighPotatoCitrusSweet PotatoCantaloupeSquashEggplantHoneydewCapsicumCucumberAsparagusBeansTomato

High relative humidity and that “just picked” fresh look can be maintained during display by occasionally misting leafy vegetables and water-tolerant crops with clean cold water. A simple sprinkler device can be constructed by perforating a pipe with tiny holes and connecting it to a hose.

Lastly, when commodities are displayed at outdoor markets, shade should always be provided.

There are many post-harvest handling practices that can be used by small-scale or low input growers, packers, shippers, and marketers of fruit & vegetable crops. This course has shown you a small sampling of techniques and information on post-harvest handling. The use of post-harvest technologies can go a long way in aiding the entire post-harvest journey. These low-cost, simple technologies will help small-scale handlers to maintain quality and reduce post-harvest handling losses of fruit & vegetable crops.