Reducing Cherry Damage in Packinghouse Operations-Packinghouse Evaluations
Objectives and Procedures
Our objective was to determine the severity of pitting and bruising damage caused by individual operations in Bing cherry packinghouses and to identify possible methods of reducing damage.
Damage to Fruit by
Our studies were conducted in 10 cherry packinghouses during the 1993 and 1994 seasons. Houses were located in California, Oregon, and Washington. At each facility we collected fruit samples before and after major unit operations in each packingline. Seven to 11 operations were sampled in the packinglines, depending on the equipment design. Each line was sampled 3 times on the same day. The packinglines were operated normally, except in 2 houses, where the fruit throughput levels were varied to test the effect of throughput on fruit damage. A marker (yellow fruit or a golf ball) was placed on the conveyor coming out of the bin dump and samples of 30 to 100 fruit each were collected after the marker passed by each sampling location. As quality may vary greatly from one bin to another, this procedure was developed to minimize error caused by bin-to-bin variation. In 7 additional houses, we measured the level of damage caused just by the cluster cutter; in 4 of these houses, the cutter belt speed was varied and damage level tested at each speed.
Effect of Fruit Throughput on
At two packinghouses, we evaluated the effect of fruit throughput on pitting damage. The amount of fruit flowing over the packingline was varied from 4 to 11 tons per hour by adjusting the speed of the conveyor lifting fruit out of the bin dump. No other belt speeds were changed. Fruit was sampled after each major unit operation in the lines.
Contribution of Cherry
We assessed damage caused by the woody end of the cherry stem by specially harvesting fruit. Fruit was removed from the tree by cutting the stems near their point of attachment to the tree. A bin of these fruit and a bin of conventionally picked cherries from the same trees were run through the same packinghouse and quality samples were collected at various points in the packingline.
All fruit samples were held for 1 to 2 weeks in polyethylene bags, placed in a 32°F cold room. Samples were then warmed to room temperature for a day and evaluated. An individual fruit was classified as pitted if it had at least one small, distinctly sunken area (pit) greater than 2 millimeters in diameter or bruised if it had a large, soft, flat or indented area with no distinct division between the damaged area and the rest of the fruit.
Pitting damage in packing is calculated as the percent of pitted fruit leaving the operation minus percent pitted entering the operation divided by the percent unpitted fruit entering the operation. Pitting expressed with this ratio corresponds to the amount of pitting caused by an operation if all the incoming fruit were free of pits. Bruising damage is calculated similarly. This allows operations with differing levels of incoming damage to be compared.
Packinghouse Surveys: Damage to Fruit on
Fruit damage before and after packing. Average fruit quality for the 10 packinglines tested is shown in Table 1. Pitting level of incoming fruit averaged 35% and packinghouse operations pitted an average of 39%, resulting in an average total pitting level of 58% in packed fruit. Our definition of a pit is fairly severe and much of the pitted fruit was very marketable. Bruising level of incoming fruit was 19% and packing operations bruised 10%, resulting in bruises on 27% of the packed fruit. In spite of the variability in the data, it is clear that a great amount of damage occurs before the fruit enters the packing operation. Packing tended to cause more pitting than bruising damage.
Contribution to damage of individual packing operations. Damage caused by unit operations in the packinghouses is shown in Table 2. Fruit in packinghouses A, B, H, I, and J was hydrocooled and stored for a short time before packing. The other five operations packed uncooled fruit on the same day the fruit was picked.
Bin dumping caused an average of 6% pitting damage and 0% bruising in the packinglines. The bin dumping operations were all similar, except for a dry dump in packinghouse C and a field box dumping to a conveyor in packinghouse F. Fruit bins are tilted and fruit drops into a water bath. A flighted, inclined conveyor lifts the fruit out of the water and conveys it to the deleafing operation. We did not notice any design or operational differences (except see Note 1 on Table 2) that would explain why several of the dumps had high damage levels.
The deleafing operation is an air separator that removes leaves from an open conveyor without moving or touching the fruit. It usually included a transfer from an inclined conveyor belt to a bar conveyor. Deleafing caused very little pitting or bruising damage.
The cluster cutters were all saw-type units. Fruit is conveyed past plastic tines that are positioned at a shallow angle, pointing against fruit flow. Clusters of fruit catch on the tines and a moving conveyor belt causes the stems to move into a saw which severs the stem. Cluster cutters pitted an average of 20% and bruised 3% of the fruit.
The flighted conveyor, small fruit eliminator, and hand sorting caused very little damage. In some lines, the eliminator and hand sorting appeared to reduce damage, perhaps because the fruit removed at these operations had a greater portion of pitted and bruised fruit than the packable fruit had.In-line hydrocooling, particularly the shower-type hydrocoolers, caused significant amounts of pitting and bruising. Immersion coolers caused little damage.
In packinghouses A and C, fruit exiting the hydrocooler dropped more than 10 inches to a flighted, inclined conveyor. This transition caused a great amount of damage. Using water between the hydrocooler and the inclined conveyor caused no damage.
The sizer, which is the same type of diverging roll sizer used earlier to eliminate small fruit, caused a similar low level of pitting damage, although the sizers in 3 packinghouses cause some bruising damage.
Box filling caused fairly low amounts of damage in general.
Packinghouse unit operations caused less bruising than pitting. Greatest bruising levels were measured in hydrocooling. The sizer and cluster cutter also caused some bruising in several packinghouses.
A More Detailed Evaluation of Damaging Unit Operations
Video footage of the operation revealed the possible damage mechanism. Cherries passing through the cutter sometimes strike the points of the plastic tines. If a cherry hits the tines squarely, it will bounce back and momentarily move against the flow of fruit. We hypothesized that cutters with slow belt speeds might cause less damage than those with fast belt speeds. To test the effect of belt speed, 3 cluster cutters were operated at a normal speed and a slower speed. Slowing the belt speed reduced pitting in all 3 houses (Table 3).
We conducted another test at 1 packinghouse where the cluster cutter belt had an electronic speed control. We ran the belt at 4 speeds, from 84 fpm to 172 fpm, to see if there was a speed above 90 fpm that would cause little or no damage. The results plotted in Figure 1 indicate that low damage levels are obtained only at the slowest speed, close to 90 fpm.
The damaging effect of the cluster cutter tines was confirmed in laboratory tests. A drop of 1 inch onto the tip of the tine caused almost 90% of the cherries to be pitted. A cherry dropping 1 inch reaches a speed of 140 fpm.
Two packinghouse managers indicated they had trouble keeping cluster cutters free of clogged fruit at speeds near 90 fpm. Although we have observed cluster cutters that normally operate with belt speeds near 90 fpm, most operate at speeds above 160 fpm. In practice it may be best to equip cluster cutter belts with speed control and operate them as slowly as possible without causing fruit clogging.
The packinghouses with high fruit throughput appeared to have lower levels of damage. This observation was confirmed in the fruit throughput test, reported later.
We also tested 2 cluster cutters that used a smooth inclined stainless steel surface to move the fruit past counter-rotating shearing wheels. One machine pitted 32% and the other 29% of the fruit that went through them. These machines do not have plastic tines but they have oscillating fingers in front of the shearing wheels. Video footage of the cutter showed that some fruit was hit by the fingers and was accelerated up the incline. This probably caused the fruit damage.
Hydrocoolers are known to damage some vegetables because of water falling great distances from the distribution pan to the fruit. We compared pitting damage level with the water drop height in the shower-type coolers. The height was measured from the shower pan to the conveyor belt. Several coolers had a water diffusing screen installed below the shower pan. For these, water drop height was measured from the screen to the conveyor. The data in Figure 2 show clearly that pitting is low if the water drop is low. Water damage can be virtually eliminated by installing a fine mesh screen (similar to window screen) below an existing shower pan. Installing expanded metal screens with a 3/4" to 1" opening below the shower pan reduces damage, but lowest damage levels were obtained with using the fine mesh screen. Screen should be parallel to the conveyor belt, keeping the maximum water drop to less than 8 inches.
The hydrocoolers in houses H and I were immersion types, where water does not fall directly on the fruit. They caused no detectable damage. Immersion coolers work well only for fruit that does not require much cooling because they remove heat at a slower rate than shower-type coolers. Shower coolers are needed to quickly cool fruit from field temperatures to 32°F.
The shower coolers that caused high levels of pitting also caused high levels of bruising.
Reducing water drop height will also reduce cherry bruising damage.
Sizer and eliminator
Sizers and eliminators caused very little pitting damage to the fruit. In fact, our tests often indicated that the fruit quality out of the units was sometimes better than that of the fruit entering the units due to elimination of small fruit. We noticed that bruising damage was the primary type of damage in sizers that caused damage. Also, small fruit was more bruised than larger fruit. We tested this observation in packinghouses E, F, and G by collecting separate small and large fruit samples of the outgoing fruit. The data in Table 4 show that small fruit sized in these 3 houses is subjected to more bruising than the large fruit. The damage is probably caused by the fruit dropping 6" to 10" from a conveyor to a fiberglass distribution pan. These drop heights would not be expected to cause much damage but the pan oscillates up and down which would, on the up stroke, increase the relative speed between the cherry and the hard surface. Other researchers have shown that smaller diameter fruit is more susceptible to bruising than large diameter fruit. Small fruit may also be more easily damaged because it tends to be less mature than large fruit.
Packinghouse A in Table 2 had a 10" drop out of the hydrocooler to a flighted conveyor which pitted 27% of the fruit. Packinghouse C had a similar drop and had 30% pitting between the hydrocooler and the sizer. Sizers caused little pitting damage, so most of the damage probably was caused by the drop to the cleated conveyor. Lines A and C had drops from the cluster cutter to a flighted inclined conveyor, but little damage occurred. These drops were only about 6 inches high and the low drop height may have reduced damage. Much of this damage probably was from the fruit hitting raised cleats on an inclined conveyor belt. This damage can be prevented by using a water transfer, where the fruit falls into a water bath and the conveyor lifts the fruit out of the water.
There was no significant effect of rate of fruit throughput (tons/hr) on the level of cherry damage when comparing average pitting damage of incoming versus outgoing fruit (Figures 3 and 4). Individual operations in the two packinghouses did not show any effect of fruit throughput rate except for the cluster cutter. Figure 5 shows that fruit pitting decreases as fruit throughput in the cluster cutter increases. A 6' wide cluster cutter is usually operated at 8 to 10 tons per hour or more. Cluster cutters should not be operated at low fruit throughput rates for prolonged periods unless the cluster cutter belt speed is low.
Cut stem fruit
Cherries without the woody stem end did not appear to cause any less damage in harvest and transport to the packinghouse than conventionally harvested fruit. Figure 6 shows that the 2 types of fruit arrived at the packingline with identical levels of pitting damage. Damage levels were also nearly the same for the packed fruit. There appears to be no measurable amount of pitting in the packing operation caused by the woody stem ends.
- Most bruising occurs before the fruit reaches the packinghouse.
- Packing operations tend to cause more pitting than bruising damage.
- Cluster cutter pitting damage can be reduced by slowing the belt speed or increasing the fruit throughput of the cutter. Installation of a variable speed controller would allow the cluster cutter operator to minimize the speed and still obtain good fruit throughput. Saw-type cutters should be operated at high capacities as often as possible.
- Shower-type hydrocoolers with high water drop heights cause fruit pitting and bruising. Hydrocoolers should be designed to minimize the distance between the shower pan and the fruit. Installing a fine mesh screen 8 " above the hydrocooler belt eliminates pitting damage.
- Immersion coolers do not cause significant amounts of pitting damage.
- Diverging roll sizers cause little pitting damage but may cause some bruising damage to small sized fruit.
- Cherries falling 10" to a cleated conveyor belt are subject to pitting.
- In all unit operations except the cluster cutter, fruit throughput rate is not correlated with pitting damage.
J. Thompson(1), J. Grant(2), G. Kupferman(3), J. Knutson(1), and K. Miller(3)
(1)Biological and Ag. Engineering Department, University of California-Davis, Davis, CA 95616.
(2)University of California Cooperative Extension, San Joaquin Co., Stockton, CA 95205.
(3)WSU Tree Fruit Research and Extension Center, Wenatchee, WA 98801.
Tree Fruit Postharvest Journal 6(1):18-26