There are many traditional methods of holding onions for transportation and/or storage that do not fit into conventional packaging classifications. These include 'string of onions', shelves and loose bulk In 'string of onions' packing, the bulbs are tied together by means of their tops to produce a bunch of bulbs is also a form of packaging. This is suitable for transporting small quantity of crop, and during storage, the bunches are hung from the roof or from special racks. Shelves for onion handling and storage are made from either wooden slats or metal mesh on a wooden or metal frame, and are usually fixed in position with the bulbs loaded and unloaded in the store. Ventilation (natural or forced) is usually achieved by passing air over the shelves. To achieve adequate aeration of the bulbs, the depth of bulbs on the shelves should be limited to 10 cm.

Onions are also stored loose bulk (instead of containers) by heaping the bulbs directly on the floor or elevated platform. Because they are not restrained, the bulbs roll during store loading to completely fill the storage space. Bulk storage permits maximum utilisation of store space, and uniform aeration is easier to achieve than in stacks of bags or other rigid packaging.

However, where bulk storage is to implemented, the retaining walls must be strengthened when storing larger quantities of bulbs, and arrangements need to be made for rebagging before subsequent marketing. It is also difficult to inspect bulbs regularly under these storage conditions. Loose bulk handling of onion is most suitable for large-scale operations where forced ventilation can be provided during long-term storage. Soft cultivars (which are also generally sweet) 'Vidalia Sweets' should not be stored in loose bulk because of their high susceptibility to compression and impact damage.

Onions can be packaged and stored in a variety of containers such as boxes, cartons, bags, bulk bins, pre-packs, plastic film bags, and stretch-wrapped trays. Packages typically contain 25 kg and above, especially for transporting crop from field to store and/or during storage. The same 25 kg bags or smaller bags may be used from store to market place. Decision on which type of packaging to use depends on crop size, length of storage and marketing requirements. A problem with packaging onions in boxes, net bags and bulk bins is that if they are too large, and airflow pattern tends to be around rather than through them. Under this condition, the respiration heat of the bulb results in a warm, humid environment in the centre of the package, which can result in decay or sprouting. To avoid these problems in large stores, the capital investment in packaging may be quite substantial.

Onion Bags

Sacks and nets used for onion packaging fall into three groups: (i) general-purpose jute sacks, as used for many agricultural commodities, (ii) open-weave sacks of sisal-like fibre, (iii) open-mesh nets, normally of plastic materials and (iv) big bags, used alternatively to crates, containing up to 1000 kg . Jute sacks are readily available in most developing countries, but their disadvantages include: (i) generally too large - may contain 100 kg onions, hence difficult to handle and an increased risk of mechanical damage; (ii) bulbs are not visible through the fabric, and it is difficult to monitor condition during storage; (iii) there is some resistance to airflow if they are used in an aerated store; (iv) difficult to label effectively; and (v) recycled sacks may encourage spread of post harvest diseases.

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