Successful sweet potatoes storage is paramount to growers. Upon harvesting, initial storage temperature typically ranges from 12 to 15°C (54 to 59°F). For five to ten days, sweet potatoes are in most cases exposed to temperatures between 26 and 29°C (79 and 84°F). This allows the starch to convert to sugar, allowing the sweet aroma to develop. These optimum conditions make it possible to maximize the net results of the harvested crop—allowing up to twelve months in maintaining a high, consistent quality. Growers can then have a year round supply of the tubers, and consumers have readily-available sweet potatoes at every grocery store visit.
The sweet potato continues to gain world-wide favor. They are versatile, contain complex carbohydrates that provide energy, and are very rich in nutrients. In the United States, several regions are particularly suited to growing success, year after year. The largest region is in North Carolina, where the climate is warm and particularly favorable. The popular Covington variety is mainly cultivated there. Other high-volume growing areas include the southern states of Louisiana and Mississippi, and also California.
A small portion (approx. 12 to 20%) of the marketable roots are washed, graded and packed within a few days of harvest and immediately shipped to buyers. These roots are referred to as “green” and are typically not as sweet as cured sweet potatoes. The majority of sweet potatoes are cured immediately upon harvest to improve flavor and storage life. Curing heals cuts and reduces decay. It also reduces the amount of shrinkage in storage. This is largely due to the thickening and reforming of the periderm. Curing also converts some starches to sugars, which enhances flavor.
Some growers begin initial storage at cooler temperatures. Many begin curing within one to two hours of harvest and continue for four to seven days at 80 to 85°F (27 to 30°C) temperature and 90 to 95% relative humidity (RH), plus ample ventilation for about five days. Rooms with 100% RH should be avoided, so that the surface of the sweet potatoes will not be completely wet, resulting in increased disease. Earlier in the season, when the soil and air temperatures are higher, the roots will cure in a shorter time than later in the season when the roots start out cooler.
Storage temperatures are critical. Long-term storage areas should be maintained at 55 to 60°F with 85% RH, with sufficient venting to produce a total volume change of air at least once a day. Above 60°F (16°C), internal breakdown, shrinking and sprouting can occur. Temperatures below 55°F (13°C) may cause hardcore, a disorder where a whitish, hard area appears in the cooked sweet potato. Properly cured and stored sweet potatoes can be held up to 12 months with little reduction in quality. Shrinkage occurs at one to two percent per month if cured, and two to five percent if uncured. In some cultivars, pithiness also increases with length of storage.
Sweet potato growers can add a protective treatment at the time of storage to increase the likelihood of storage success. Treatment is seen as added insurance, whether any sign of decay is present or not. Signs of decay can be hidden, or develop through the course of storage. With a chemical treatment, you gain the peace of mind that decay sources are stopped early in the storage process. Treatments can be easily applied, leave no residue, and sweets are safe for consumption shortly after application.
For years, root crop growers have partnered with Industrial Ventilation, Inc. (IVI) for treatment application at the point of storage. Some growers utilize the treatment upon the sight of decay in storage (a remedial effort), and the following year, schedule treatment at the point of storage (for prevention). Why? They see the success delivered by the treatment, and see the application at the point of storage, even with no signs of decay, as the insurance needed to help protect their precious crop. It is a relatively small investment given the potential cost of loss.
Maximize the lasting quality of your stored sweet potatoes with an added layer of protection. FruitGardTM protects for the long haul in storage, and attacks at any point of decay.
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– September 28, 2018
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