General operations
Dumping
Washing
Waxing
Sorting
Sizing
Fruit packing line
Packinghouse operations can be as simple as moving produce from a field lug into a shipping container, or may include a variety of handling practices, from cleaning, waxing, sizing, and quality grading to color sorting. The provision of shade during the packing operations is extremely important. Shade can be created using palm leaf fronds, a plastic mesh or canvas sheet hung from temporary poles, or via a permanent roofed structure. When deciding upon where to locate a packinghouse, access to the field and market point, adequate space for vehicles to enter and leave the packinghouse and ease of access to labor will all be considerations (Proctor, 1985).
In the simplest packinghouse, produce is delivered in picking containers, immediately after harvest, directly to the packers. The packers then sort, grade, size and pack the produce directly into appropriate transport containers. In this case, each worker must be knowledgeable regarding produce defects, grade and size requirements, and packing methods.
As the size and complexity of the packinghouse increases, more operations and workers trained in specific tasks might be added.
Dumping
Produce must somehow be removed from the field bin or harvesting container and moved through the packinghouse. This first step is known as ''dumping". Dumping must be done gently, whether using water assisted methods or dry dumping. Wet dumping can decrease bruising and abrasions by using moving, chlorinated (100-150 ppm) water to carry delicate produce. When using dry dumping, padded, sloped ramps or moving conveyor belts can decrease injuries to produce.
Pre-sorting
Pre-sorting produce is usually done to eliminate injured, decayed, or otherwise defective produce (culls) before cooling or additional handling. Pre-sorting will save energy in that culls will not be handled. Removing decaying produce items will limit the spread of infection to other units, especially if postharvest pesticides are not being used.
Cleaning
For some commodities, such as kiwifruits and avocadoes, dry brushing may be sufficient to clean the produce. Other commodities, however, such as bananas and carrots, require washing. The choice of brushing and/or washing will depend upon both the type of commodity and the type of contamination.
Sanitation is essential, both to control the spread of disease from one item to another, and to limit spore buildup in wash water or in the packinghouse air. Chlorine treatments (100 to 150 ppm Cl) can be used in wash water to help control pathogen buildup during packing operations (Moline, 1984). There is some variation in the strength of bleach available commercially in different countries, but a rule of thumb is to use 1 to 2 mls of chlorine bleach per liter (1 to 2 ounces of chlorine bleach per 8 gallons of clean water). Walls, floors and packing equipment can also be cleaned using quarternary ammonium compounds labelled as safe for food processing equipment (Kupferman, 1990).
Waxing
Waxing of immature fruit vegetables such as cucumbers and summer squash; mature fruit vegetables such as eggplant, peppers and tomatoes; and fruits such as apples and peaches is common. Food grade waxes are used to replace some of the natural waxes removed in washing and cleaning operations, and can help reduce water loss during handling and marketing. If produce is waxed, the wax coating must be allowed to dry thoroughly before further handling.
Sizing
Sizing produce is optional but may be worthwhile if certain size grades receive a higher price than others. In most low-input packinghouses, manual sizing is still commonly practiced. Operators should be trained in selecting the size desired and to either directly pack the items into containers or place the selected produce gently into a bin for packing further down the line. Sizing can be done subjectively (visually) with the use of standard size guages. Examples of the smallest and largest acceptable sizes for each product can be placed within view of the operator for easy reference. Hand held sizers are used for a variety of products.
Several types of mechanical sizers are available for small scale operations. One type is composed of a long slanted tray with a series of openings which converge (largest at the top, smallest at the bottom). This type of sizer works best with round commodities. Other sizers are designed as conveyors fitted with chain or plastic belts with various sized openings, and are useful for sizing most commodities. Another simple method for mechanical sizing is to use a set of diverging bar rollers (see illustration below), where the smallest sized produce falls through the rollers first to a sorting belt or bin, and larger sized produce falls between successively more divergent rollers.
Diverging bar rollers sizer:
The typical series of operations in a packinghouse are illustrated below. Dumping can be done using either dry or water-assisted methods, depending upon the sort of produce being handled. Cleaning, as well, can be by washing with chlorinated water or dry brushing alone. Waxing, if practiced, occurs after washing and removal of surface moisture. Grading, as illustrated, separates the product into processing and fresh market categories. Sizing further separates the product, with the smallest size going to the local market or to processing. Typically, the best quality produce is packaged and marketed at the regional or national level.
FAO. 1986. Improvement of Post-Harvest Fresh Fruits and Vegetables Handling - A Manual. Bangkok: UNFAO Regional Office for Asia and the Pacific.
The following is a flow diagram of packinghouse operations. The number and size of packing lines will depend on the kinds and quantities of produce that are handled each day.
Source: Kader, A.A. 1993. Postharvest Handling. In: Preece, J.E. and P.E. Read. The Biology of Horticulture - An Introductory Textbook. New York: John Wiley & Sons, Inc. pp. 353-377
Any time produce is dumped from one container into another, care should be taken to reduce mechanical damage to the commodity. When dumping produce from field bins or from transport vehicles into the packinghouse, dry or wet dumping can be practiced. When using dry dumping practices, the filed container should be emptied slowly and gently onto a tilted ramp with padded edges. In the illustration below, a conveyor belt then carries the dry dumped produce into the packinghouse.
Dry dumping
Wet dumping is sometimes used to reduce mechanical damage, either by dumping into water rather than onto a dry ramp, or by immersion and floatation. If the specific density of the produce, such as apples, is lower than that of water the produce will float. For some produce, such as pears, salts (such as sodium lignin sulfonate, sodium silicate or sodium sulfate) must be added to the water to increase its specific density and assure fruit floatation.
The canvas curtain illustrated below is used to break the fall of fruit moving from a conveyor into a bulk bin.
Source: USDA. No date. Modernising Handling Systems for Florida Citrus from Picking to Packing Line Agricultural Research Service, USDA Marketing Report No. 914.
Steel drums can be used to make a simple washing stand. The drums are cut in halt fitted with drain holes and all the metal edges are covered with split rubber or plastic hose. The drums are then set into a sloped wooden table. The table top is constructed from wooden slats and is used as a drying rack before packing.
Because steel drums are often used to store petroleum and chemical products, they should be thoroughly cleaned before being used as a washing stand.
Source: Grierson, W. 1987. Postharvest Handling Manual. Commercialization of Alternative Crops Project. Belize Agribusiness Company/USAID/Chemonics International Consulting Division.
This tank for washing produce is made from galvanized sheet metal. A baffle made of perforated sheet metal is positioned near the drain pipe and helps to circulate water through the produce. Fresh water is added under pressure through a perforated pipe, which helps move floating produce toward the drain end of the tank for removal after cleaning.
Improvements to the design shown below might include a removable trash screen in front of the baffle, and/or a recirculating system for the wash water (with the addition of chlorine).
FAO. 1989. Prevention of Postharvest Food Losses: Fruits Vegetables and Root Crops. A Training Manual. Rome: UNFAO. 157 pp.
The waxing device illustrated here is designed to be used after a series of dry brushes on a conveyor line. Industrial wool felt is used to distribute the liquid wax to the fruits or vegetables from a trough made the same width as the belt. Evaporation of wax from the felt is reduced by covering the felt with a layer of heavy polyethylene sheeting.
Source: Martin, D and Miezitis, E.O. 1964. A wipe-on device for the application of materials to butts. Field Station Record Volume 3 No. 1 CSIRO Tasmanian Regional Laboratory, Hobart, Tasmania.
Sorting/Packing
The table illustrated below is a combination sorting and packing stand. Incoming produce is placed in the sorting bin, sorted by one worker into the packing bin, and finally packed by a second worker. If workers must stand to sort produce, a firm rubber pad for the floor can help reduce fatigue.
Source: FAO. 1986. Improvement of Post-Harvest Fresh Fruits and Vegetables Handling- A Manual. Bangkok: UNFAO Regional Office for Asia and the Pacific.
The surface of the portable sorting table illustrated below is constructed from canvas and has a radius of about 1 meter (about 3 feet). The edges are lined with a thin layer of foam to protect produce from bruising during sorting, and the slope from the center toward the sorter is set at 10 degrees. Produce can be dumped onto the table from a harvesting container, then sorted by size, color and/or grade, and packed directly into shipping containers. Up to 4 sorters/packers can work comfortably side by side.
Source: PHTRC. 1984. A portable sorting table. Appropriate Postharvest Technology 1(1):1-3. (Post-Harvest Training and Research Center, Department of Horticulture, University of the Philippines at Los Banos.)
The following illustrations represent three types of conveyors used to aid sorting of produce. The simplest is a belt conveyor, where the sorter must handle the produce manually in order to see all sides and inspect for damage. A push-bar conveyor causes the produce to rotate forward as it is pushed past the sorters. A roller conveyor rotates the product backwards as it moves past the sorter.
Belt conveyor:
Push-bar conveyor
Roller conveyor:
Source: Shewfelt, R.L. and Prussia, S.E. 1993. Postharvest Handling: A Systems Approach. San Diego: Academic Press Inc. 356 pp.
When sorting for rejects, and removing any product that is too small, decayed or damaged, the height of the sorting table should be set at a level comfortable for sorters. Stools, or a firm rubber pad on which to stand, can be provided to reduce fatigue. Locations of the table and the sorting bins should be chosen to minimize hand movements.
It is recommended that the workers' arms create a 45 degree angle when s/he reaches toward the table, and that the width of the table be less than 0.5 meter to reduce stretching. Good lighting will enhance the ability of the sorter to spot defects, and dark, dull belts or table tops can reduce eye strain.
If a conveyor system is in use, the product must not flow too fast for the sorters to do their work. The rotational speed of push-bar or roller conveyors should be adjusted to rotate the product twice within the immediate field of view of the worker.
Source: Shewfelt R.L. and Prussia, S.E. 1993. Postharvest Handling: A Systems Approach. San Diego: Academic Press Inc. 356 pp.
Round produce units can be graded by using sizing rings. Rings can be fashioned from wood or purchased ready-made in a wide variety of sizes.
Single size hand held sizing ring:
Multiple size rings:
Source: FAO. 1989. Prevention of Postharvest Food Losses: Fruits, Vegetables and Root Crops. A Training Manual. Rome: UNFAO. 157 pp.
The rotary cylinder sizer illustrated below is composed of five hollow cylinders which rotate in a counterclockwise motion when driven by an electric motor. Each cylinder is perforated, with holes large enough to let fruits drop through. The first cylinder has the smallest diameter holes, and the fifth has the largest holes. When fruits fall through, they are caught on a slanted tray (the chute), and roll into the containers as shown. Take care that the distance of the drop is as short as possible to prevent bruising. Oversized fruits are accumulated at the end of the line. This equipment works best with round commodities.
Source: Reyes, M. U. (Ed.) 1988 Design Concept and Operation of ASEAN Packinghouse Equipment for Fruits and Vegetables. Postharvest Horticulture Training and Research Center, University of Los Baños, College of Agriculture, Laguna, Philippines.
The onion sizing table illustrated below is one of three (or more) tables used in a stairway fashion. Each table is made of plywood, and has been perforated with holes of a specific size. The uppermost table has the largest size holes, and the lowest table has the smallest holes. A layer of onions is dumped onto the uppermost table. Those that do not pass through are classified as "extra-large'' in size. Those that pass through fall into a mesh bag and roll into a large container. This container of onions is dumped onto the second sizing table. The onions that do not pass through are classified as "large", and so on.
Source: Reyes, M. U. (Ed.) 1988. Design Concept and Operation of ASEAN Packinghouse Equipment for Fruits and Vegetables. Postharvest Horticulture Training and Research Center, University of Los Baños, College of Agriculture, Laguna, Philippines.
The pommelo sizer illustrated below is composed of a rectangular chute made of plywood, padded with foam to prevent bruising. The fruit is dumped into the octagonal platform at the top of the chute, then allowed to roll, one by one, down toward a series of constrictions. Large fruits are caught in the first constriction, medium in the second, and small in the last. Undersized fruit passes out the end of the chute directly into a container. Workers must manually remove each fruit and place it into the appropriate size container before the next fruit can pass through the chute. The sizing is fastest when five workers are stationed at the sizer.
Source: Reyes, M. U. (Ed.) 1988. Design Concept and Operation of ASEAN Packinghouse Equipment for Fruits and Vegetables. Postharvest Horticulture Training and Research Center, University of Los Baños, College of Agriculture, Laguna, Philippines.
If a conveyor system is used in the packinghouse, a wide variety of sizing chains and belts are available for sorting produce. Sizing chains can be purchased in many widths and in any size opening.
Square openings are usually used for commodities such as apples, tomatoes and onions, while rectangular openings are used for peaches and peppers. Hexagonal openings are often used for potatoes and onions.
Square:
Rectangular:
Hexagonal:
Source: 1994 Catalog of TEW Manufacturing Corporation, P.O. Box 87, Penfield, New York 14526 USA
Small scale equipment for packing produce is available from several manufacturers and suppliers. Illustrated below is a fruit packing line, available from TEW Manufacturing Corporation at a cost of less than US$ 5000. This particular model includes a receiving belt, washer and sorting table.
Source: 1994 Catalog of TEW Manufacturing Corporation, P.O. Box 87, Penfield, NY 14526 USA
