Sweet Potato Storage in Bangladesh: Curing, Temperature and Avoiding Chilling Injury

Sweet potato (mishti alu) is widely grown in Bangladesh, much of it as a winter rabi crop, including on char lands and riverbanks where it fits well into sandy soils. It is often treated as a humble crop that needs no special storage. Yet farmers and traders regularly lose part of their harvest to rot, shrinkage, sprouting and pests in the weeks after digging. The most important thing to understand about storing sweet potato is that it is not an ordinary potato. The cold that keeps table potatoes in good condition will damage sweet potatoes, and that single misunderstanding causes a large share of losses.

Why sweet potato is a chilling-sensitive crop

Sweet potato is a tropical root crop. Like tomato, banana and several other tropical produce items, it suffers chilling injury when held at low temperatures that are still well above freezing. Published postharvest guidance, including the USDA Agriculture Handbook 66 on commercial storage of fruits and vegetables, generally places the chilling threshold for sweet potato at around 10 to 12°C, with longer exposure causing more damage.

Chilling injury often does not show immediately. Roots may look normal when they come out of cold storage, then develop internal browning, a hard core that will not soften on cooking (sometimes called hardcore), poor flavour, pitting on the skin and fast decay once returned to warm temperatures. Traders can be caught out because the damage appears in the market, not in the store.

Why standard potato cold stores are the wrong place

Most cold storage capacity in Bangladesh was built for table potatoes and seed potatoes, which are held at low temperatures to prevent sprouting over several months. Our article on seed versus table potato storage explains those regimes. Putting sweet potatoes in the same chamber exposes them to temperatures well below their chilling threshold. A trader who stores sweet potatoes in a potato cold store to wait for a better price may find that the stock rots quickly once it is taken out, turning a storage decision into a loss.

The lesson is that sweet potato needs a room held at a moderate temperature with high humidity. In practice that usually means a separate chamber or a mini cold storage set to a different point from potato stores, which is one reason a smaller dedicated room can make sense for traders who handle sweet potato in volume.

Curing: the step most growers skip

Curing is a short period of warm, humid holding immediately after harvest that lets the roots heal the skin damage caused during digging and handling. During curing, the root forms a protective layer of cells (wound periderm) under cuts and scrapes. Cured roots lose less water, resist rot organisms better and store considerably longer. Curing also converts some starch to sugar, which improves eating quality.

Published guidance generally recommends curing at around 29 to 32°C with relative humidity of roughly 85 to 90 percent for about four to seven days, with ventilation to remove carbon dioxide. Bangladesh’s natural conditions during parts of the harvest season can come close to these ranges, but humidity and temperature both need to be managed, not assumed. Roots cured in a dry, breezy shed may shrivel instead of healing.

Storage conditions after curing

After curing, the same published sources place long-term storage at roughly 13 to 15°C with relative humidity around 85 to 90 percent. Below that temperature range, chilling injury becomes a risk; above it, roots sprout, lose weight faster and develop more rot. Good air circulation around crates or bins prevents warm spots.

• Store in ventilated crates or boxes rather than tall heaps, which crush lower layers and trap heat.
• Keep humidity high enough to limit shrivelling but avoid water dripping onto the roots.
• Check stock regularly and remove rotting roots before rot spreads.
• Keep sweet potatoes away from fruits that give off large amounts of ethylene, which can affect sprouting and quality.

These are general ranges from published postharvest literature; the exact settings should be confirmed for your variety, how long you intend to store, and your market. Ask us to design a room built around your volumes and storage period.

Handling from field to store

Most storage losses begin at harvest. Sweet potato skin is thin and easily damaged, and every cut or bruise is an entry point for rot fungi such as Rhizopus soft rot. Digging when soil is moist but not waterlogged, lifting roots carefully rather than pulling on vines, and avoiding throwing roots into bags all reduce injury. Roots left in hot sun after digging can suffer sunscald, and roots left in the field during cold nights at the end of the winter season can be chilled before they ever reach a store.

Pests are another concern. The sweet potato weevil (Cylas formicarius) is a major pest of the crop in South Asia, and infested roots develop tunnels and a bitter taste. Weevil damage can continue in storage, so infested roots should be separated at sorting rather than stored with clean stock. Our broader guide to reducing post-harvest loss covers sorting and grading principles.

Transport and market considerations

Sweet potato often travels long distances from growing areas to Dhaka and other markets in open trucks. Tight stacking in sacks crushes roots, and long delays in hot vehicles raise rot risk. When shipping in refrigerated transport alongside other produce, set the temperature for the sweet potato rather than sharing a load set for cold-loving vegetables. Our article on refrigerated transport explains mixed-load decisions. For traders considering processing into chips, flour or frozen products, the same quality principles apply to the raw material; see our guide on agro-processing machines.

A worked example: planning storage for a local trader

Imagine a trader in a northern district who buys sweet potatoes from char farmers at harvest, when prices are lowest, and wants to hold part of the stock for several weeks to sell as prices recover. The first decision is whether storage is worthwhile at all, which depends on the price difference the trader expects against the cost of storage and the weight lost during it.

If it is worthwhile, the plan follows the crop’s biology. Roots are bought directly from careful harvesting, sorted on arrival to remove cut, bruised and weevil-damaged roots, and cured under warm, humid conditions for several days. They then move into a room held in the moderate temperature range described above, in ventilated crates, with humidity monitored and stock checked weekly. The trader sells first from any lots that show signs of decline. This is very different from simply renting space in the nearest potato cold store, and it is the difference between storage that adds value and storage that destroys it.

Common mistakes and their consequences

• Storing with potatoes in a standard cold store. Chilling injury leads to rapid rot and hard, unappealing roots after removal.
• Skipping curing. Uncured roots lose more weight and rot sooner, shortening the storage period.
• Rough harvesting and bagging. Skin damage becomes the entry point for soft rot.
• Storing weevil-damaged roots with clean ones. Pest damage spreads and reduces saleable stock.
• Ignoring humidity. Dry storage causes shrivelling and weight loss, which directly reduces income for a crop sold by weight.

If you trade or grow sweet potatoes at a scale where storage matters, a small dedicated chamber set up for curing and moderate-temperature storage may be worth evaluating. We can supply mini cold storage equipment from China and help you specify it; contact us for a quote built around your volumes and storage plans.

Related reading: cold storage for potatoes and vegetables, ginger curing and sprout control, and tomato chilling injury. To see how we handle sourcing, freight and clearance end to end, visit our services page, browse the shop, look at our China sourcing and buying agent service, or contact DE International for a quote built around your actual products and volumes.