Cherry Damage Surveys in 1993
Funding was provided by the Washington Tree Fruit Research Commission, the California Stone Fruit Marketing Board, and the Washington Stone Fruit Marketing Committee. Research and surveys were undertaken by Drs. Galen Brown (USDA-Michigan), Jim Thompson and Joe Grant (UC-Davis), Tim Facteau (OSU), Steve Drake (USDA-Wenatchee), Carlos Crisosto (UC-Kearney), Mike Meheriuk (Ag. Canada), and myself.
I have been asked by the program committee to react to the conclusions of these studies, a number of which will be repeated in 1994. The following is an abbreviated report of the design of the studies and their conclusions. The complete reports are available upon request. For obvious reasons it is not possible to reveal the names of the packinghouses involved.
Dr. Galen Brown
Dr. Brown offered the following suggestions from his experience in Michigan:
- Warm fruit bruise less severely than cold fruit
- Poron cushions (1/8-1/4") on hard surfaces reduce bruising
- Slides should replace drops at transfer points
- Fruit falling on stems can become pitted
- Dark skinned fruit bruise as easily as light skinned varieties
- Larger fruit can be pitted more easily than small fruited varieties
His observations on the equipment used on cherries in the Pacific Northwest included:
- 10- 19 transfers per line
- 4-12 drops onto hard surfaces
- Total drop heights of 23-135 inches
- Average drop height to a hard surface of 6-14 inches
- Cherries hit the bottom of water flume lines
Dr. Brown's overriding philosophy is that the industry must modify each operation so that "zero-damage occurs"--anything above this is not acceptable. He suggests:
- Reduce the total number of transfers
- At transfers reduce drop height by adding cushions or slides
- Change dry transfers to water transfers
- Increase the depth of the water in flumes
- Reevaluate methods of dumping fruit from bin
- Develop optical sorting for size, defects, and color
- Use air-cushion trucks for distance transport
- Line picking buckets
Obviously some of these suggestions will be relatively easy to implement while others need further study. Dr. Brown's complete report is available from the Tree Fruit Research Commission.
Hebert Research, Inc.
They concluded that bruising and pitting were the most serious of the cherry defects. After 14 days of storage, they found that 21% of all the fruit showed moderate to severe bruises and that 14% of the fruit were pitted.
Their research indicated that more than half of the bruises were already on the fruit by the time it reached the packinghouse. They determined that 53.6% of the total bruising was already on the fruit upon arrival at the packinghouse. Fruit picked directly off the tree already had 17% of the total bruising. More work is needed to define where this fruit is bruised prior to reaching the packinghouse. Growers need to take steps to reduce bruising.
On the other hand, Hebert's research this season indicated that only 15.8% of the fruit which was to develop pitting had been damaged by the time it reached the packinghouse. Thus, almost 85% of the pitting was a result of the packing process. Pitting occurred most seriously during hydrocooling, box filling, sorting, sizing, and bin dumping. Few pitted fruit (3%) were found on the tree.
Dr. Jim Thompson
Bing cherries from four packinghouses (different from those used by Hebert) in Washington and California were collected before and after the major operations on the packinglines. Yellow fruit were used as markers and each line was sampled three times. Fruit were held at 32°-34°F in poly bags for one week, followed by 24 hours at room temperature prior to being evaluated.
Cluster cutters were examined at seven additional packinghouses and fruit was sampled at normal cluster cutter height. After adjustments were made to cluster cutters, more fruit was run through and sampled. Similar tests were done at the hydrocoolers, automatic box fillers, and sorting tables.
Pitting damage as a result of packing practices was the focus of the study and it was found to vary greatly between houses.
This study found that bin dumping caused about 10% pitting damage in the four packinglines. One of the four had a dry bin dumper, but damage was no different than that resulting from wet dumping. The rate of dumping, the height of fall of the fruit, and the method of removing the last fruit from the bin play a great role in determining the amount of pitting.
A great deal of attention was paid to the cluster cutter. Video footage showed that the cherries sometimes strike the points of the tines and bounce back. High fruit through-put, low tine adjustment, and slower belt speed resulted in fewer pitted fruits. These factors make a major difference in the amount of pitting caused by the cluster cutter.
The in-line shower type hydrocooler appeared to be a factor in the amount of pitting. The height of the shower pan in different packinghouses ranged from 20 inches to 8 inches above the fruit. Less damage appeared to occur to fruit when the shower pan was lowered. This is rather simple to do by adding a drilled metal sheet or a fine mesh expanded metal with 1/4" openings.
As fruit emerges from the hydrocooler, it often drops a long distance onto an elevation belt with flighted conveyors (cleats). Damage occurs as the fruit strikes the cleat. It can be reduced by using a water transfer between the hydrocool conveyor and the elevator.
Finally, this study showed that, once the fruit is in the box, sorting through the cherries can cause significant damage. Two minutes of hand sorting caused a 50% incremental increase in pitting. It may be necessary to "touch up" fruit at the top of the box, but sorting through the box, especially with big gloves on, is detrimental.
In summary, their suggestions for reducing pitting within the packinghouse are:
- Operate the cluster cutter belts as slowly as possible and maintain high fruit throughput in the cluster cutter without clogging the machine
- Lower the cluster cutter tines to almost touch the belt
- Add a lower shower pan to reduce water height in hydrocoolers
- Use water transfer between horizontal and flighted conveyors
- Do not hand sort cherries after they are in the box
Bing cherries were carefully hand harvested and hydrocooled within three hours to the desired temperature. Fruit remained in the water for as short a period as possible. Cherries were dropped individually through PVC pipe onto a flat surface, a dimpled surface, or the woody portion of a cherry stem from a height of 3, 6, or 12 inches. Each treatment was repeated three times. Fruit were held at 32°-34°F for two weeks plus 24 hours at 70°F in poly bags prior to being evaluated. Washington fruit were evaluated for bruising and pitting.
As would be expected, more bruising and pitting occurs to cherries dropped from greater heights than from less height on any surface. Fruit dropped onto a dimple belt will be more damaged than fruit dropped onto a flat hard surface and damage occurs at a lower height. Fruit dropped onto a cherry stem would be intermediate to the other treatments.
The effect of temperature is more interesting. Pitting appeared to be less when warmer temperature fruit were handled than when the fruit were colder. This was not true in all lots and locations tested but was the general trend.
Hebert's work indicates that bruising, not pitting, occurs in fruit at ambient (warm) temperatures. Running fruit across the packingline at too warm temperatures may increase bruising while reducing pitting.
I think that the time interval between harvest and packing should be considered. If fruit are to be packed soon after harvest, perhaps they should not be held at very cold temperatures. It is important to remove the field heat. It is critical to pick during the coolest part of the day and immediately take the fruit to the warehouse.
I remain convinced that temperature is the best defense (besides having excellent quality fruit) to deterioration and decay. As cherry fruits do not contain stored carbohydrates, firmness, sugars, and acidity are lost very rapidly unless the fruit is cold. Cherries that are not well below 40°F when shipped do not arrive in good condition.
Temperature management must balance the rapid loss of quality experienced by warmer fruit with the ability of warmer fruit to resist forces that may cause damage.
We will further explore these temperature relationships during the 1994 cherry season as well as evaluate additional packinglines in Washington State.
Dr. Eugene Kupferman, Postharvest Specialist
WSU Tree Fruit Research and Extension Center
1100 N. Western Ave., Wenatchee, WA 98801
Tree Fruit Postharvest Journal 5(1):17-19