Chapters 8.4
8.4 - Hermetic grain storage bags
Gryphon Theriault-Loubier, University of Guelph, Canada
Suggested citation for this chapter.
Theriault-Loubier,G (2022) Hermetic grain storage bags. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org
Introduction
Though often overlooked, effective and affordable food storage technology desperately needs implementation in the developing world to protect from a wide variety of pests such as insects, rodents, and fungi.
Hermetically Sealed Technology
Principles
Hermetically Sealed Technology (HST) has been proven to be highly effective at preserving grains in many studies. A HST, when properly sealed and maintained, prevents the exchange of oxygen and moisture between the outside atmosphere and the stored grain (IRRI, 2004). This lack of oxygen creates an anaerobic environment; pests which rely on an aerobic environment, like fungal molds and insects are effectively controlled without the use of pesticides or other inputs, which are often out of reach for subsistence farmers (Kamanula et al., 2011).
HSTs have been found to be effective for storage of rice, cocoa beans, coffee, corn, dates, flour, millet, sorghum, sugar and wheat amongst others (GrainPro Inc., 2013). HSTs maintain flavor and aroma, prevent rancidity in foods such as peanuts, control insects and rodents, reduce fungal growth, and maintain harvest weight effectively (GrainPro Inc., 2013). Importantly, HSTs have been found to maintain seed viability for extended periods (FAO, 2011).
In a comparison with commonly used woven polypropylene bags (WPG), hermetic grain bags (HGB) were found to cause 99.5% mortality within 60 days of some common Sub-Saharan African maize pests that were artificially placed in the bags (Ognakossan 2013). In the same study, loss of grain was between 0.5-6% using HGB compared to 19-27% in WPG. Moisture rates were also maintained in the hermetic grain bags while moisture losses occurred in the WPG.
In an economic analysis of maize storage technologies in Kenya, Kimenju and De Groote (2010) presented the results of six-month crop storage loss trials in comparing metal silos, HSTs, a common pesticide and a standard woven polypropylene bag as control. Standard polypropylene bags were found to have the highest loss (24%), compared to the HST (6.3%), and metal silos (0.5-1.7%). While metal silos are perhaps a more effective means of storage in-place, they are not portable and not practical financially for a subsistence farmer (World Bank, 2011). Kimenju and De Groote (2010) noted that metal silos would take in excess of ten years to recoup the investment, whereas HSTs have the benefit of a relatively low initial investment and high return-on-investment. In fact, hermetic sacks are being bartered in some communities throughout Africa, as they are viewed as a high value commodity (FAO, 2011). An HST, effectively implemented, benefits farmers by allowing them to control when they sell their grain, and preventing the surplus at the end of the harvest which diminishes commodity prices for all farmers (Kimenju and DeGroote, 2010).
The World Bank does note that construction of mud silos in areas that do not traditionally use them has been effective (World Bank, 2011). For example, in northern Ghana 1,000 mud silos were commissioned by the Ministry of Food and Agriculture and associated organizations. It was found that in these areas, mud silos were effective in increasing effective crop storage time and preventing pest access, accounting for only 6.5 percent of losses over the study period as compared to jute bags and traditional granary structures (World Bank, 2011). However, construction of these silos requires the availability of suitable timber, which is sparse, and maintenance of the silos in the long term casts doubt over the ability of these silos to continue to offer such benefits (World Bank, 2011). Also, food security issues have encouraged individuals to store grain in their homes (often in the bedroom), and HSTs are more suitable for this (World Bank, 2011).
Critical Analysis
Grain needs to be suitably dried before being hermetically stored. Weinburg (2008) found that it is possible to store higher moisture content grain in HST, however losses do occur; it is still preferable, where possible, to dry grain adequately. Therefore, high humidity climates might find limited use if no effective method for drying foods can be practiced. The International Rice Research Institute (IRRI) estimates that to effectively reduce spoilage of foods inside HSTs, grains need to be dried to less than 12-14% moisture content depending on species (IRRI, 2010).
An HST needs to be kept protected, as any punctures leading to air leakage will minimize the benefits of the technology. To protect the bag, manufacturers recommend placing the HST into an existing type of storage such as a jute bag or woven polypropylene bag. To check for leaks, manufacturers suggest gently fill the bag with air, tying the bag shut, and placing a light book or hand on top, while observing the bag to check for air loss.
The Cowpea Bag
A variant of the HST is the Purdue Improved Cowpea Storage bag, which is a triple layer bag. It includes an outer protective layer and has been found to be quite effective in the protection of cowpea from a number of insects. Purdue maintains an extensive library of videos and information on their cowpea bag.
Purchase
The International Rice Research Institute (IRRI) co-developed one of the leading HST technologies with GrainPro Inc. GrainPro maintains an international distribution network, which is easily accessed through their site.
Large commercial systems cost about $100-130 per tonne, with an expected product life-cycle of at least ten years. Smaller scale ‘Super Bags’ cost approximately $1-2 depending on the volume of order and shipping destination. If protected from physical damage, they have been confirmed to last six growing seasons or more.
The cowpea bag can be purchased by visiting the Purdue website and consulting region specific dealers.
Practical tips
The International Rice Research Institute recommends that the grain should be dried to 12-14% moisture content. The HST should be placed inside an existing woven polypropylene bag or jute bag to provide protection. After the HST is filled with dried grain, excess air should be removed. The top of the bag should be twisted and folded into two, then tied with an elastic band or tape. The protective outer bag should also be closed. A very helpful and beautifully illustrated PDF is available through Purdue with many tips and basics
Picture Based Lesson to Train Farmers
For the South Asian version (pictures only, text for you to insert), click this link for lesson 9.4:http://www.sakbooks.com/uploads/8/1/5/7/81574912/9.4_south_asian.pdf
For the East/South Asian version (pictures only, text for you to insert), click this link for lesson 9.4:http://www.sakbooks.com/uploads/8/1/5/7/81574912/9.4e.s.a.pdf
For the Sub-Saharan Africa/Caribbean version (pictures only, text for you to insert), click this link for lesson 9.4:http://www.sakbooks.com/uploads/8/1/5/7/81574912/9.4subsaharan_africa_carribean.pdf
For the Latin-America version (pictures only, text for you to insert), click this link for lesson 9.4:http://www.sakbooks.com/uploads/8/1/5/7/81574912/9.4latin_america.pdf
Source: MN Raizada and L Smith (2016) A Picture Book of Best Practices for Subsistence Farmers. eBook, University of Guelph Sustainable Agriculture Kit (SAK) Project, June 2016, Guelph, Canada.
Further Information
The International Rice Research Institute has excellent information on grain storage (http://www.knowledgebank.irri.org/rkb/grain-storage-systems.html), and detailed information on hermetic storage including practical tips (http://www.knowledgebank.irri.org/rkb/grain-storage-systems/hermetic-storage-systems.html
References
1. Ali, S., & Villers, P. (2002). Cocoons dramatically reduce pests in store. Appropriate Technology, 29(3), 20-20.
2. Baoua, I. B., Amadou, L., Margam, V., & Murdock, L. L. (2012). Performance of triple bagging hermetic technology for postharvest storage of cowpea grain in Niger. Journal of Stored Products Research, 51, 81-85.
3. Chen, S., Zhang, M., & Wang, S. (2011). Effect of initial hermetic sealing on quality of ‘Kyoho' grapes during storage. Postharvest Biology and Technology., 59(2), 194-199.
4. Edoh Ognakossan, K., Tounou, A. K., Lamboni, Y., & Hell, K. (2013). Post-harvest insect infestation in maize grain stored in woven polypropylene and in hermetic bags. International Journal of Tropical Insect Science, 33(1), 71-81.
5. IRRI Knowledgebank
6. Kimenju, S. and De Groote, H. (2010) Economic Analysis of Alternative Maize Storage Technologies in Kenya. Contributed Paper presented at the Joint 3rd African Association of Agricultural Economists (AAAE) and 48th Agricultural Economists Association of South Africa (AEASA) Conference, Cape Town, South Africa, September 19-23, 2010.
7. Johnson, J. A., & Zettler, J. L. (2009). Response of postharvest tree nut lepidopteran pests to vacuum treatments. Journal of Economic Entomology, 102(5), 2003-2010.
8. Weinberg, Z. G., Yan, Y., Chen, Y., Finkelman, S., Ashbell, G., & Navarro, S. (2008). The effect of moisture level on high-moisture maize (zea mays L.) under hermetic storage conditions-in vitro studies. Journal of Stored Products Research, 44 (2) Pp.136-144.
9. World Bank. (2011). Missing Food: The Case of Postharvest Grain Losses in Sub-Saharan Africa. World Bank, Natural Resources Institute, and Food and Agriculture Organization of the United Nations. 1-116.