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Hermetic storage: a viable option

The 150 tonne National Seed Storage site in Kigali, Rwanda  (Philippe Villers)
The 150 tonne National Seed Storage site in Kigali, Rwanda
Philippe Villers

One of the oldest forms of food preservation in the world, hermetic storage, provides an airtight, safe and pesticide-free means of storing dry food commodities. However, whilst the oldest form of hermetic grain storage discovered in North Africa and the Middle East involved underground sealed pits, modern methods use large, flexible, plastic envelopes - called Cocoons™ or SuperGrainbags™ - to create a sealed environment where any pests present die from lack of oxygen.

In hot, humid countries, insects, moulds, and rodents can cause storage losses of up to 25 per cent. Large metal or concrete silos commonly used in more temperate climates work poorly due to moisture and condensation problems, so storing grains for long periods of time can prove a challenge. However, with modern hermetic storage, constant moisture content can be maintained. In addition, the low oxygen atmosphere in the container prevents insect damage, development of aflatoxins (a particular problem in groundnuts and maize), and loss of flavour and aroma in crops such as coffee, cocoa, and basmati rice. It also preserves the potential for germination in seeds.

A growing number of countries, including Philippines, Rwanda, Ghana and Sri Lanka, are storing rice, maize, sorghum, wheat and pulses using this modern means of airtight storage. In Rwanda for example, the government has procured hundreds of Cocoons of 50 and 150 metric tonnes capacity for village-level storage of maize, pulses and sorghum.

Avoiding famine

According to Rwanda's Eastern Province Governor, Theoneste Mutsindashyaka, use of Cocoons has prevented famine in certain parts of the region. Storing crops hermetically also allows farmers to wait until prices have increased rather than selling immediately after harvest; in Kabarore district, for instance, farmers gained a 40 per cent increase in market prices by storing grain for at least four months.

Five years of research at the International Rice Research Institute (IRRI) and three years of trials in Indonesia have shown that hermetic storage can help double the life of rice seeds, maintain good milling quality, and protect grains from pests such as insects and rodents, without using pesticides. In Vietnam, Cambodia and Laos, farmers have been trained in storing their seeds hermetically, thus increasing seed germination and seed viability and reducing the amount of seed used per hectare. One Cambodian farmer reported that he sold an additional 70 kilograms of seed, earning him an additional income of US$9 (the reusable super bag costs only $1).

Maintaining quality

IRRI's farmer-friendly Super Bag is a cheap form of hermetic storage (IRRI)
IRRI's farmer-friendly Super Bag is a cheap form of hermetic storage

Coffee is another crop that needs to be stored for long periods but quality - particularly in hot, humid climates - is known to deteriorate rapidly after three months A controlled field study conducted by Café Britt, Costa Rica, in 2003, showed that coffee stored for five months using hermetic storage maintained its quality and appearance, as well as its moisture level. According to their professional cupper: "The quality remained at 4.0 (5 point scale) for those in the Cocoon, and dropped to 3.0 for unprotected coffee beans. The superiority of coffee stored in hermetic Cocoons was very noticeable."

Other coffee growers have since obtained similar results and, more recently, to avoid deterioration of coffee quality during sea shipments, exporters have begun to use transportable, hermetic storage bags called SuperGrainbags™ (shown in Figure 2) with excellent results. This method is now used for coffee exported from Ethiopia, Costa Rica, Jamaica and Hawaii. Recent improvements in sealing the SuperGrainbags promise even longer storage.

From low to high tech

After 25 years of proven scientific trials and field experience, a large range of mainly dry commodities ranging from rice and wheat, to figs, coffee and seeds are now stored using a flexible plastic envelope as hermetic storage. In most cases a low-oxygen atmosphere is achieved naturally with the respiration of any insects present and the commodity itself producing CO2. Where rapid fumigation is desired, as with figs in Turkey, Gas-Hermetic Fumigation using injection of CO2, or Vacuum-Hermetic Fumigation - as with narcissus bulbs in Israel - are used as means of accelerating the natural process.

Hermetic storage is a practical technology and can be adapted for the protection of commodities in quantities as small as a conventional grain bag to bulk of many thousands of tonnes. Most importantly, it is user-friendly and environmentally benign, making the use of pesticides and fumigants unnecessary during storage, thus protecting farmers and consumers from the associated risks of chemicals or development of aflatoxins.

Written by: Philippe Villers

Date published: January 2008


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