Post-harvest management

After harvesting, the tubers should be dried off as fast as possible within the first 24 hours to allow wound healing and to prevent rotting. Drying off is done by avoiding high humidity and condensation and providing positive ventilation. Freshly harvested tubers should not be washed, unless if they are meant for immediate cooking.

For storage, the cured tubers are preferably carefully placed in boxes or crates, or are packed into open mesh bags, such as those used for onions to allow sufficient air circulation and to limit hot and humid conditions. Bruising of the tubers should be avoided throughout as open wounds provide entry points for diseases and also can result in water loss from the tubers and shrivelling.

For short-term storage of 1 to 2 weeks, ware potatoes may be stored at ambient temperatures in a dark cool, dry, well-ventilated buildings. The potatoes are better kept spread, rather than in a large heap or enclosed in tight containers. Small-scale farmers can keep potatoes in on-farm storage using inexpensive, well-ventilated constructions. If available, storage can allow the farmers to plan marketing better, or to target window markets when prices are higher.

For longer storage, up to four months potatoes need to be stored at temperatures of 4 to 6 °C in special cold storage units or rooms at a relative humidity of 90 to 95 %. Industrial potatoes should not be stored below 8 °C. Often, such cold storage facilities are not readily available to smallholder farmers, or local traders. Long-term storage may not be available within a reasonable distance, may be too expensive or even not necessary, as price fluctuation may not be high due to continuous harvest of potatoes throughout the year in Cameroon.

Only potatoes with a strong skin are suitable for long-term storage. Therefore, before long-term storage and after drying off potato tubers are best kept for 3–4 weeks in a dry and airy place at ideally about 12 °C, or for 2 weeks at 15 °C to promote corking and wound healing, and reduce rot. Condensation of moisture on the walls of the storage unit indicates insufficient insulation (or ventilation?).

After drying-off (curing), the tubers are cooled slowly at maximally 0.5–0.7 °C per day (or 1–2 °C per week). The difference in temperature between the tubers and the outside air at ventilation should be at least 2 °C. To avoid weight losses, the warmth can be transferred from the stored tubers to the walls and ceiling by regularly circulating air, which increases the humidity. Before sorting, washing or packing cooled potatoes should be warmed up to at least 10 °C to avoid susceptibility to damage.

Storage temperature should not be too low, as it causes tubers to shrink and lose weight. Storage under overly humid conditions increases the risk of diseases, condensation and rotting. Tubers become damp and sprout easily.

Ventilation is necessary to ensure sufficient airflow and to regulate humidity. Airflow varies depending on storage practices. Airflow is best, when tubers are stored on racks, is medium in sacks and is lowest in piles or heaps.

Sprouting of seed potatoes and potatoes for consumption can be reduced using plant tonics based on spearmint oil and unsaturated fatty acids (commercial name ‘Mitobar’). Due to the mint oil’s intense smell, overdosage should be avoided in case of short-term storage. Citronella, caraway, clove and rapeseed oil inhibit sprouting of potatoes as well. These natural substances have an intense smell. Also, ethylene can be used according to the EU-Organic Regulation to inhibit sprouting of potatoes during storage.