Bruise reduction basics

Bruises can occur in many areas of potato handling, but potential for bruising is greatest during harvest.
Rosalie I. Tennison
January 11, 2018
By Rosalie I. Tennison
What potato grower wouldn’t want to add dollars to their bottom line? By reducing the bruising that occurs during harvest by one percent, thousands of dollars could be added to the bank, according to research completed at the University of Maine. The solution is to minimize the potential for bruising before the harvester enters the field, but growers in a hurry often overlook this most basic crop management rule.

“Without a doubt the part of any potato operation that causes the most damage is the harvesting equipment,” says William Bohl, a now retired extension educator from the University of Idaho, and author of several papers on harvest management and bruise prevention. “Even with new machinery, you may have to make adjustments.”

According to Bohl, bruised tubers can result in shrinkage during storage, disease introduction to the pile, less consumer appeal and loss of product. All of these factors can lead to lowered prices and rejected loads, which can equate to a loss of income. Therefore, it is worth taking time before entering the field to ensure the harvester is in optimum condition and the operator is trained properly.

There are tools available to help growers calibrate their harvesting equipment, but there are a few basics that every grower should know, such as beginning with clean, well-maintained equipment with no loose parts that might impede the safe and uninterrupted delivery of the potatoes to the truck. Secondly, ensure operators are properly trained on the operation of the equipment so they understand the importance of bruise prevention and careful handling. A properly maintained harvester operated by a diligent operator will deliver the crop to storage with minimal bruising.

Beyond those basics, understanding how the parts of the harvester work together and making adjustments will ensure efficiency. Generally, potatoes bumping into potatoes will not cause bruising, but stones and chunks of hard soil bumping into potatoes will.

Ideally, a conveyor filled to capacity, leaving no room for potatoes to bounce, roll around or hit harder objects, will minimize problems.

“Run your harvester full, really full, because potatoes are safer if they move in a huge mass,” says Steve Johnson, a crop specialist at the University of Maine. Johnson is publisher of a fact sheet that is widely used in eastern Canada and the United States that instructs growers on how to calibrate their equipment for top efficiency.

“Properly adjusted harvester conveyor speeds are based on harvesting ground speed,” adds Bohl. “To adjust conveyor speeds, harvesting ground speed must first be determined.”

Once the calibrations are made to match the chosen ground speed, all operators must be instructed to maintain that speed. Bohl used research from Washington State University to design a “Harvester Adjustment Worksheet” that assists growers to make and record their equipment calibration.

In addition to ensuring the conveyor speed works with the ground speed, other adjustments that should be made to reduce bruising at harvest include: blade position, primary and secondary conveyors, conveyor chain, rollers and deviner. Adjustments to any or all of these can effectively reduce bruising overall.

Bohl says to position the blade and primary nose cone rollers so the potatoes flow onto the upper surface of the conveyor rather than bumping into the front. “Blade designs should be matched to the soil type, soil condition, the presence of other plant roots and the depth of the tubers,” he explains. “When choosing a conveyor chain, choose one that suits your soil and operating conditions.” He says belted chains cause the least damage, but they eliminate less soil than other chains.

“Roller size and mounting location should be such that humps in the conveyor bed are minimized to prevent tuber rollback,” Bohl continues. “Be sure to replace worn rollers as needed.” On the primary conveyor, he suggests covering the centre support bars with padding and replacing it often because it will frequently wear out.

Bruising often occurs on harvesters and windrowers when tubers strike the links of the deviner chain, Bohl continues. He suggests covering the deviner chain links with cushioning material.

“To reduce bruising, the rear crossover chain should be covered to provide maximum cushioning,” advises Bohl.

“A big issue is how the potato drops,” says Johnson. Therefore, minimizing the length of the drop and ensuring the landing is soft can do a lot to reduce bruising during harvest, he says. “It’s worth the time to get your calibrations and timing correct.” He says that some processors are now insisting on daily checks on equipment as part of their contractual agreement with growers.

“Making sure every aspect of tuber handling is done correctly is an economic value to growers,” Johnson states. He says there are many tools available to help growers manage their harvesting equipment to minimize bruising and, considering to the significant economic impact of having too many bruised potatoes in a load; growers should be taking advantage of them.

Finally, Bohl reminds growers to ensure all employees who operate equipment or are involved in the harvesting operation are properly trained and aware of bruise reduction strategies. Harvester operators and others should be continually on the lookout for equipment problems that may be damaging tubers. “Ideally, growers should implement a bruise management program that encompasses all aspects of potato production from planting through harvest,” he says.

The goal of potato harvest is always to deliver a bruise-free crop to customers and, by taking a day to calibrate and adjust all parts of the harvester, that one day of salary could multiply into thousands more dollars on your bottom line. 

From the Potaoes in Canada magazine archives.

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