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.
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 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.
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.
Wash before cooling and packing : tomatoes, cucumbers, leafy greens
Wash to remove latex, reduce staining: mangoes, bananas
Wash after storage : sweetpotatoes, potatoes, carrots
Dry brush after curing or storage: onions, garlic, kiwifruit
Do Not Wash : green beans, melons, cabbage, okra, peas, peppers, summer squash
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 quaternary ammonium compounds labeled as safe for food processing equipment (Kupferman, 1990).
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 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 gauges. 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.
Many products have established U.S. grades and standards that can assist packers in sorting and sizing produce. The following are examples of standards based upon diameter and/or length.
Examples of USDA Grade Standards:
|U.S. Fancy||> 1 inch||> 10 inches|
|U.S. No.1||> 3/4 inch||> 10 inches|
|U.S. No.2||> 1/2 inch||> 10 inches|
|Garlic size designations||Diameter in inches|
|#11 Super-Colossal||2 15/16 and up|
|#10 Colossal||2 11/16 – 2 15/16|
|#9 Super-Jumbo||2 7/16 – 2 11/16|
|#8 Extra-Jumbo||2 3/16 – 2 7/16|
|#7 Jumbo||1 15/16 – 2 3/16|
|#6 Giant||1 13/16 – 1 15/16|
|#5 Tube||1 11/16 – 1 12/16|
|#4 Medium Tube||1 9/16 – 1 11/16|
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 University of Wisconsin is promoting this handling system for produce because it saves time, money and is safer for handlers. With a hand pallet truck you can move up to 16 cartons at a time. This system can cut your time spent moving boxes and will dramatically reduce the stress on your body.
A hand pallet truck is similar to a regular hand truck (dolly) except that the base uses pivoting forks instead of a fixed plate metal shoe. If you stack your load on a small plastic pallet (14 x 24 inches), you can position the forks underneath and move an entire stack of cartons at once. A hand pallet truck can be tilted (by releasing the forks) for loading and unloading and locked into an upright position to tip back and roll the load.
According to the UWisconsin project, custom-made hand pallet truck and pallet costs approximately $750. At $7.00 per hour, you'd need to save 107 hours for the system to pay for itself. If you saved 30 minutes per weekday (10 hours per month), the system would pay for itself in less than 11 months. The pallet truck system also saves money in reduced back pain and therefore fewer visits to the doctor, chiropractor or a massage therapist. If you saved yourself 15 visits (at $50/visit), the system would pay for itself.
Source: University of Wisconsin Healthy Farmers, Healthy Profits Project, December, 2000; Work Efficiency Tip Sheet: Narrow Pallet System Second Edition.
Custom hand trucks available from: Valley Craft, 2001 South Highway 61, Lake City , MN 55041 . (800) 328-1480. [email protected]
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.
Packing operations that are done in an unsystematic manner can cause delays, add costs or effect produce quality. You can save time and money by laying out the packing shed in an organized, step-by-step system.
Source: Meyer et al. 1999. Work Efficiency Tip Sheet: Packing shed layout. Healthy Farmers, Healthy Profits Project, Department of Biological Systems Engineering, College of Agricultural and Life Sciences, University of Wisconsin, 460 Henry Mall, Madison, WI 53706.
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 field 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.
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.
To reduce bruising:
Source: Thompson et al. 2002. Preparation for fresh market. pp.67-79. In: Kader, A.A. (ed). Postharvest Technology of Horticultural Crops. University of California , Division of Agriculture and Natural Resources, Publication 3311.