Weight Sizing Color Sorting And Packaging Apples Pears Peaches Nectarines Plums and Apricots

Several manufacturers offer graders or sizers with high-speed carrier systems capable of handling 12 to15 fruit per second and accurately segregating them based on weight with an accuracy of +/- 1 gram (Figure P1.1). These systems are used frequently in handling and sorting individual apples, pears, apricots, nectarines, and peaches. Some cultivars of pears with irregular shapes or elongated necks

FIGURE P1.1. Commercial packing line with 'Golden Delicious' apples prior to color grading and weight sizing (Source: Photo courtesy of Stemilt Growers, Wenatchee, WA.)

make handling more difficult. Most of this equipment has camera options available for capturing color images of the entire surface of each fruit. Using computer control systems, sorting decisions can be made based on programmable criteria and the amount and shades of color present on each fruit. Fruit color standards (and also quality and packing grade standards) have been established by the U.S. Department of Agriculture and other government and private agencies (http://www.ams.usda.gov/standards/frutmrkt.htm). In some situations, nonmechanized packing occurs directly out of picking containers into trays, and the packer performs all sorting and sizing functions manually.

Hand packing machine-sorted fruit into shipping and retail display cartons has long been a strenuous and labor-intensive operation. Loose filling boxes can be accomplished mechanically, but fruit must be bruise resistant and tolerant of the impacts that occur in this method. Recently, robotic equipment has been developed that handles this delicate operation at commercially viable speeds approaching 1.5 boxes per minute.

Fruit-packing orientation and materials are very important. Fruit that look good going into the shipping carton may not look good upon arrival at their destination because the wrong packing materials were used. During shipping, fruit are exposed to vibrations and changes in acceleration that can result in significant bruising. Compression bruising can also appear if cartons collapse or fruit are packed too tightly. If fruit are not immobilized in the carton, they can develop scuffing marks from the friction of vibration. All these factors can result in the rejection of the product by retailers and/or consumers. It is imperative to select packing materials that protect the fruit, minimize weight loss, are lightweight to reduce shipping and energy costs, and are recyclable and environmentally friendly.


Optical sorting equipment, developed in Walla Walla, Washington (http://www.keyww.com/), for use in the food-processing industry, has been adapted and used in sorting cherries based on color. This equipment relies on multiple cameras positioned to observe individual cherries that are distributed into individual lanes on a vibratory conveyor and then launched into the air for surface color evaluation. The computer processors are extremely quick to recognize cherries

"in-flight," capture the surface color information, and then make a determination as to whether fruit meet specific criteria. The decision to reject an individual fruit based on its lack or abundance of a color is made, and the cherry is blown out of its trajectory by a series of individually controlled air jet nozzles. The nozzles deliver enough air pressure to divert individually selected fruit to a separate water flume for transport to a separate packing area. This equipment is very sophisticated and is capable of processing up to 14 metric tons of cherries per hour.

Sizers in use for smaller stone fruit such as cherries are not as prevalent as those used in apples and pears. Weight sizing for cherries is impractical due to time restrictions of singulating individual fruit and the large volume of fruit being processed by commercial packing operations. Cherry sizers have been developed to sort fruit based on fruit dimensions instead of weight. However, cherries also create special problems with respect to size, since they are not spherical or symmetrical and are harvested with stems attached. The first cherry sizers were developed using inclined, diverging rollers. Gravity and water assist cherries as they traverse downward along the sloping, spinning rollers. Smaller fruit exit the rollers near the top of the incline while the largest fruit travel to the largest gap at the lower end of the rollers. Four or five water flumes under the rollers carry the "sized" cherries to box-filling equipment.

The latest technology in cherry sizing is a system developed in Wenatchee, Washington (http://www.stemilt.com/). This technology also relies on stainless steel rollers that rotate at over 300 rotations per minute, but the rollers in this version are parallel. The number of parallel zones and their gap width determine the number of sizes to which cherries can be sorted. The cherry sizer is computer controlled and capable of changing roller gaps to the nearest 0.1 millimeter. Each sizing lane is capable of sizing more than 1.5 metric tons of cherries per hour.

The fact that this equipment is highly specialized and expensive is exaggerated by the reality that cherries are quite perishable and have a very narrow harvest window. The entire packing season in the northwestern United States is spread over about eight weeks due to differences in maturity timing associated with cultivar and orchard elevation. Without the high market value of cherries, this technology would not be economically feasible.


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