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Sweet Potato Storage Research Aids Success for Growers

Close up of red/purple skinned sweet potatoes

Growers are sweet on storage. They know that a successful duration of sweet potatoes in storage means the work that began at planting has paid off to the highest degree possible. Continuing research strives to find the best possible conditions for the optimal outcome of stored sweets. Variables are tested and re-tested at the university level, as well as by food processing companies. One such company is Lamb Weston. The motivation behind this research is to help growers provide the absolute best crop possible, as it benefits both grower and processor. When a company like Lamb Weston receives an excellent supply of sweet potatoes, it sets the stage for a optimal processing and a very high-quality product for kitchen operators and ultimately, consumers.

For many years, IVI has been an industry leader in root crop storage, particularly potatoes and onions. IVI’s systems and products are now leveraged for the benefit of sweet potato growers. Adjustments are made to the unique requirements of sweet potatoes, but IVI’s success with other root crops are benefiting outcome for stored sweets. IVI has been a resource for Lamb Weston scientists working on storage research efforts that show great promise for growers.

Sweet potato storage success is growing, thanks to research.

Lamb Weston is headquartered in Eagle, Idaho, and its reach with its extensive line of food offerings is international. Many of their products are sweet potatoes, from fries to mashed to roasted. Their processing level varies with each product, and the best outcome of their frozen products starts with a high-quality sweet delivered by growers.

Much of their research is stationed in Louisiana, in the heart of sweet potato-growing country. Jeremy Higley, Principal Scientist, co-leads this effort with other Lamb Weston scientists and agricultural experts. There are many factors that come into play. One thing is for certain: these storage research efforts are benefiting growers and processors.

Their research is focused on how modern methods of storage can improve storage success for growers. According to Higley, a lot of the historic research included varieties of sweet potatoes that are not widely grown. Sweet potato variety is one of many factors to consider, and storage conditions may shift slightly to optimize for a particular variety, from Beauregard, to Covington, Bayou Belle, and many more.

The Lamb Weston sweet potato storage testing containers from the outside.
Some of the test storage units at Lamb Weston. Small-scale testing mimics larger-scale conditions, and if promising, can be applied to larger storage buildings.These units hold up to six large storage bins.

Let’s start with the dirt on dirt.

When it’s harvest time, growers have to consider the dirt. Moisture condition of the ground can dictate harvest timing. Depending upon the crop volume, a degree of mechanization aids harvest, typically bringing sweets to the surface. The skin on sweets is particularly delicate at harvest. As the sweets are moved to bins, sorting is often done by hand, for quality control and tender handling. Keeping surface damage, or scuffing, to a minimum helps avoid problems in storage.

Another factor with dirt is the amount that is brought into storage. Dirt adhering to sweets inhibits air flow, and can also negatively impact the skin, potentially leading to disease.

The perfect curing temperature is indeed the cure all.

Sweet potato storage bins being loaded by a fork lift into a test storage container.
Bin being loaded into test storage. These storage units have both temperature and humidity control.

Once bins of sweets are stacked in storage, the temperature for curing is paramount. This storage first step sets the stage for ideal, long-term holding, and it increases sugar content. 85° F is the temperature found by many researchers to be ideal. Lamb Weston’s Jeremy Higley describes a three-to-five-day period at this temperature, or until signs of sprouting start. Curing is also best stopped when wounds, or scuffing and skinning, heal. The healing of surface wounds can prevent rot in storage. The sweets are now set for longer-term holding.

Now it’s time to chill.

55-60° F provides the ideal storage temperature after the curing stage. Maintaining this consistent temperature is key, according to Higley. Chill injury is one threat to stored sweets. Maintaining relative humidity at 90-95% is also critical. Another important element is air flow. The goal is even circulation to all bins, and this means going through bins, not around. The method of stacking bins can help to this end. Controlling air flow can be aided by devices that utilize exterior air flow, providing a very low cost of operation, such as IVI’s Thermadoor. Utilizing a CO2 sensor is another important factor in creating ideal storage conditions.

Minimizing weight loss is the goal in sweet potato storage.

A view inside of the Lamb Weston sweet potato storage testing containers.
These rolling platforms on the inside are load cells that continuously record weight, so loss can be monitored during storage.

All the parameters noted previously provide control of conditions in storage. Together, they increase the likelihood of preserving the level of quality of sweets going out of storage as going in. However, one thing is inevitable with stored sweets: weight loss. Higley explains that “…sweet potatoes are living and metabolizing in storage. Starch and sugars are metabolizing, plus there is a degree of moisture loss. As such, weight loss in unavoidable. What is key is the degree of loss.”

Optimizing storage conditions can minimize weight loss, as well as prevent disease. If growers are storing from October through April or May, for example, weight loss can generally range from 6-8%, or 10-12% in larger commercial operations. These ranges occur with solid environmental control in storage. What happens if one factor is diminished? Growers can see loss increase two-to-three times the rate, or as much as a 20% loss. “Controlling temperature and humidity is critical for storage success,” says Higley.

Research done at the university level and by companies such as Lamb Weston are aiding growers with preventing a level of loss that does not have to occur if storage control is optimized, offering a level of insurance for growers. This is especially true when growers are planning long-term, high-volume storage. Companies like Lamb Weston find sweet potatoes that lack optimal quality are more difficult to process. Helping growers helps processors. “Modern storage methods and buildings can benefit the quality of sweet potatoes and reduce post-harvest loss,” says Higley.

Sweet potato storage research is moving the industry forward.

Research and successful results for stored sweets is invaluable for the sweet potato industry. Growers who can take advantage of these control methods, storage buildings and products can better provide high-quality sweets out of storage. They can attract the best food processors seeking their crop. For food processors, it means excellent products that start with a reliable crop source, and create more efficient processing.

IVI has long been a developer of top-performing products and systems for root crop storage. These utilize the best of technology, developed by our engineers, responding to the needs of growers, as relayed by our sales and service team members. Our solutions include temperature and relative humidity control, CO2 monitoring, and air-flow devices—all orchestrated by the commands of our control panels. And, all operated with a goal of ease-in-use for growers. Our engineers also custom design storage buildings that best utilize our storage systems. Our sales and service team can help growers with chemical treatment. Like the researchers at the corporate and university level, we are always looking to advance storage success for growers.

Have questions?

Chase Kidd

Nampa, ID  |

International Sales & Global Dealer Manager

May 2, 2019