Curing of Ground Provisions
Product Care

Ground provisions (sweetpotato, yam, cassava, eddo) are underground storage organs with a thin delicate skin that is easily damaged during harvest and handling. Wounding and skin damage causes the product to have a high rate of water loss, leads to an unsightly appearance, and increases the susceptibility to postharvest decay. Proper curing of ground provision immediately following harvest is an effective way to reduce the amount of postharvest loss and increase product storage life.

What is Curing

Curing is a high temperature [(26.5-32°C) (80-90°F)] and high relative humidity (90-98% RH) treatment done immediately after harvest. The total duration of the curing treatment ranges fro 2 to 7 days, depending on the crop and environmental conditions. The temperature should not exceed 35C (95F) nor should the RH be so high (i.e. 100%) where moisture condensation occurs on the surface of the product. Free moisture will allow decay and postharvest disease organisms to enter the produce before the protective layer forms. Ventilation is needed during the curing process to introduce fresh air (oxygen) and remove carbon dioxide (CO2).

Benefits of Curing

• Naturally heals wounds of damaged areas in the skin tissue of ground provisions.
• It extends the shelf life for ground provision that is intended to be stored for prolonged periods and /or exporting.
• The stronger skin of the cured product protects against decay, reduces the amount of moisture, and extends the postharvest life.
• Enhances the culinary characteristics of some ground provisions (i.e. Sweet potato).

When to Cure

Curing should begin within 12 hours after digging. The roots/tubers should not be washed before curing, as this increases postharvest decay.

The Curing Process

There are two steps in the curing process. The first step is suberization, the production of a waxy suberin material and its deposition in the cell walls. The second steps is the formation of a cork cambium and production of cork tissue (wound periderm) several cell layers below the surface of the wounded flesh tissue. This acts as a second skin and seals the cut or bruised areas, helping to prevent decay.

Methods of Curing

Field Curing

Ground provisions can be cured outdoors if piled in a partially shaded area. Cut grasses or straw can be used as insulating materials and the pile should be covered with canvas, burlap or woven grass mats. This covering will trap self-generated heat and moisture.

Room Curing

Ground provisions are more effectively cured inside protected structures or insulated buildings with rooms designed for this purpose. Wetting the floor or using an electric humidifier can maintain a high RH. The ground provisions can be left in their field crates during curing, provided they are well ventilated and sufficiently strong enough to be stacked.

Recommended Conditions

Storage

After the ground provisions have been adequately cured, they should be moved to a longer-term storage facility. Roots and tubers which have partially deteriorated during curing should be separated from the marketable ones before storing. Successfully cured ground provisions will have a significantly longer potential storage life. This will help in marketing, by allowing for more consistent supplies for high quality product.