Benefits of Controlled and Modified Atmosphere Storage for Grains

Every year, millions of tonnes of grain are lost after harvest – not in the field, but in storage. Insects, mould, and moisture quietly destroy food that was perfectly good at the time of harvesting. In developing countries alone, storage-stage losses for cereals can reach 50-60% of the total harvest. The good news? Two closely related technologies – controlled atmosphere (CA) storage and modified atmosphere (MA) storage – are proving that we can fight these losses without relying heavily on chemical pesticides. By adjusting the gases surrounding stored grain, these methods slow down biological activity, kill insects, and keep grain quality intact for months or even years.

What are controlled and modified atmosphere storage? 🔗

At its core, both CA and MA storage work on a simple principle: change the air composition around stored grain so that insects, moulds, and the grain’s own respiration slow down dramatically. Normal air contains roughly 78% nitrogen, 21% oxygen, and about 0.04% carbon dioxide. In atmosphere-controlled storage, oxygen levels are reduced – often to below 2% – while carbon dioxide or nitrogen concentrations are increased inside a sealed storage structure.

The key difference between the two techniques lies in the level of ongoing control. In controlled atmosphere storage, gas concentrations are continuously monitored and adjusted throughout the storage period using automated systems with sensors, gas cylinders, and computerized feedback loops. This approach maintains precise gas levels, typically within ±1% of target values.

Modified atmosphere storage, on the other hand, involves an initial change to the gas composition – after which the atmosphere is not actively managed. Over time, the gas levels inside a modified atmosphere setup will shift naturally due to the respiration of grain, insects, and microorganisms present in the sealed environment. This makes MA systems simpler and cheaper, though less precise than CA systems.

How does altering the atmosphere protect stored grains? 🔗

The benefits of atmosphere management in grain storage come from two main biological effects: suppressing respiration and eliminating pests.

Reducing respiration rate 🔗

Grain kernels are living organisms. Even after harvest, they continue to respire – consuming oxygen and releasing carbon dioxide, water vapour, and heat. Higher respiration leads to moisture build-up, heating, and eventually spoilage. By lowering oxygen and raising CO₂ around the grain, the metabolic rate of the stored commodity slows down significantly, extending its natural shelf life and preserving nutritional quality.

Controlling insects and pests 🔗

Storage insects such as grain weevils (Sitophilus species), flour beetles, and grain borers are aerobic organisms – they need oxygen to survive. When oxygen drops below roughly 2%, most stored-grain insect species cannot survive. Carbon dioxide is particularly effective: a CO₂ concentration above 35% maintained for at least 15 days at around 25°C can achieve complete disinfestation of dry grain. The lower the grain moisture content, the more effective the treatment, because drier conditions combined with low oxygen create a desiccation effect on insects.

Suppressing mould and mycotoxin development 🔗

Moulds and fungi can still grow at very low oxygen levels (as low as 0.2%), but they require grain moisture above 16% to cause serious problems. In a well-managed CA or MA system where grain is dried to below 12-13% moisture before sealing, fungal growth is effectively halted. This is critical because fungi like Aspergillus flavus produce aflatoxins – carcinogenic compounds that contaminate grain and pose serious health risks. Research has shown that high CO₂ concentrations can also reduce the aflatoxin-producing ability of these fungi.

Types of controlled and modified atmosphere storage systems 🔗

These technologies come in several forms, suited to different scales of operation and budget levels.

Large-scale commercial CA storage 🔗

Major grain elevators and processing facilities invest in sophisticated CA systems featuring sealed silos or warehouses, automated gas injection equipment, and computerized monitoring. Gases like nitrogen or carbon dioxide are supplied from external cylinders or generators and injected into the storage structure. Advanced sensors track not just gas concentrations but also temperature, humidity, and sometimes even pest activity through acoustic detection. These systems can handle thousands of tonnes of grain and are most cost-effective for high-value commodities stored over long periods.

Hermetic storage structures 🔗

Hermetic (airtight) storage is the most accessible form of modified atmosphere technology. Instead of actively injecting gases, hermetic systems rely on the natural respiration of grain, insects, and microorganisms within a sealed environment to gradually deplete oxygen and build up carbon dioxide. Over time, this self-generated atmosphere becomes lethal to insects and inhibits mould growth. Hermetic storage can range from large steel or concrete bins to smaller, more affordable options like sealed plastic containers.

Hermetic storage bags (PICS bags) 🔗

One of the most impactful innovations for smallholder farmers is the Purdue Improved Crop Storage (PICS) bag. Developed by Purdue University with funding from the Bill & Melinda Gates Foundation, PICS bags use a triple-layer plastic design to create airtight conditions. Once grain is sealed inside, insect and microbial respiration depletes the available oxygen, creating a natural modified atmosphere. Farmers can store grain for up to two years without any chemical pesticides, while retaining the grain’s taste, colour, and cooking quality.

These bags cost roughly $1-1.50 USD per unit, making them a practical solution for resource-limited farmers. Over 20 million hermetic bags have been sold across sub-Saharan Africa and parts of Asia over the past decade, and studies in eastern Kenya showed adoption rates climbing from about 54% to over 91% within just two years of introduction.

Key benefits of CA and MA storage for grains 🔗

Reduced post-harvest losses 🔗

The most significant advantage is the drastic reduction in storage losses. Properly sealed hermetic storage structures have shown up to 98% reduction in storage losses while maintaining seed viability and grain quality over extended periods. For context, scientific storage methods overall can bring losses down from 50-60% to just 1-2% – a transformation that directly translates into more food and more income for farming households.

Chemical-free pest management 🔗

Traditional grain storage often relies on chemical fumigants like phosphine (aluminium phosphide) or methyl bromide. These chemicals are effective but carry serious health risks for agricultural workers and can leave residues in the grain. Insects can also develop resistance to pesticides, forcing farmers into a cycle of using ever-stronger chemicals. CA and MA storage offer a non-chemical alternative that eliminates insect infestations through oxygen deprivation rather than toxic substances.

Preservation of grain quality 🔗

Beyond simply keeping grain alive and insect-free, atmosphere-controlled storage maintains the overall quality of the stored product. Nutritional content (including protein and fat), germination rate, and cooking properties are all better preserved compared to conventional open storage. This matters not just for food quality but also for farmers who save seed for the next planting season – the viability of stored seed is significantly higher in hermetic systems.

Extended marketing flexibility 🔗

When grain can be safely stored for longer periods, farmers gain the freedom to sell when market prices are favourable rather than being forced to sell immediately after harvest when prices are typically lowest. This price arbitrage can substantially increase a farmer’s annual income.

Challenges and limitations 🔗

Despite clear advantages, adopting CA and MA storage is not without hurdles.

Airtightness is critical 🔗

The entire system depends on maintaining an airtight seal. Any leak allows outside air to enter, restoring oxygen levels and rendering the treatment ineffective. For large-scale metal bins, achieving an adequate seal can be challenging because many structures are bolted together with numerous seams that must all be individually sealed. The key to a successful MA/CA treatment is thorough pressure testing of the storage structure before use.

Initial cost and infrastructure 🔗

Commercial CA systems require significant capital investment – sealed chambers, gas supply infrastructure, monitoring equipment, and trained operators. While large commercial operations can justify these costs through reduced losses and quality premiums, smallholder farmers often lack the capital for even mid-range solutions. Although hermetic bags are affordable per unit, the cost still represents a barrier in some of the poorest farming communities. Studies in Malawi identified perceived high cost and local unavailability as key barriers preventing adoption even when farmers were aware of the technology.

Requirement for proper grain drying 🔗

Atmosphere-controlled storage works best when grain is dried to safe moisture levels (typically below 13%) before sealing. If grain is sealed at higher moisture content, the excess moisture supports fungal growth even in low-oxygen environments. In tropical regions where drying conditions can be difficult, this requirement adds an extra step that must be done correctly for the system to work.

No residual protection 🔗

Unlike chemical treatments that may leave a protective residue, CA and MA treatments provide no ongoing protection once the storage environment is opened. After the seal is broken, the grain is once again vulnerable to insect infestation. This means that good sanitation, exclusion of pests, and regular monitoring remain necessary after treatment.

The role of CA and MA storage in food security 🔗

Globally, post-harvest losses accounted for approximately 14% of food production in 2021, and these losses are disproportionately higher in developing nations where storage infrastructure is weakest. With the global population projected to reach 9.1 billion by 2050, reducing post-harvest losses is widely seen as one of the most cost-effective ways to increase food availability – far cheaper and more environmentally sustainable than increasing agricultural production.

Hermetic and atmosphere-controlled technologies directly address the storage segment of the post-harvest chain, which is where the largest fraction of grain losses occurs in developing countries. Importantly, approaches like PICS bags and other hermetic solutions bring this technology within reach of smallholder farmers who grow the majority of the world’s food.

Government programmes, international development organisations, and cooperative models are increasingly supporting the adoption of these technologies. In Kenya, for example, the AgResults programme used a pay-for-results competition to incentivise private-sector companies to commercialise hermetic storage technologies for smallholder farmers, including PICS bags, metal silos, and plastic tanks. This type of public-private partnership is helping build sustainable supply chains for storage technologies in regions that need them most.

Looking ahead: combining technologies for better results 🔗

Research is now moving towards integrating CA and MA storage with other preservation strategies. Combining controlled atmospheres with proper temperature management (refrigerated or cooled storage) and humidity control creates comprehensive storage environments that maximise grain quality and minimise losses far more effectively than any single method alone.

There is also growing interest in modified atmosphere packaging (MAP) for processed grain products, where individual consumer packages are flushed with nitrogen or CO₂ before sealing. This approach bridges the gap between bulk storage and retail, maintaining quality right through to the consumer’s kitchen.

For smallholder farmers, the focus is on making existing solutions more accessible – through local manufacturing of hermetic bags, microfinancing schemes, better distribution networks, and farmer-to-farmer training programmes. Innovations in bag design, including more durable materials and rodent-resistant features, are also addressing some of the practical limitations encountered in the field.

What do you think? Could wider adoption of controlled and modified atmosphere storage significantly reduce hunger in food-insecure regions? What steps do you think governments and organisations should prioritise to make these technologies available to every farmer who needs them?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC5296677/
2. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/controlled-atmosphere
3. https://www.sciencedirect.com/topics/food-science/modified-atmosphere-storage
4. https://en.wikipedia.org/wiki/Controlled_atmosphere
5. https://www.purdue.edu/discoverypark/food/research/pics.php
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC7304484/
7. https://www.co2meter.com/blogs/news/6077164-controlled-atmosphere-storage-using-carbon-dioxide
8. https://www.mdpi.com/2071-1050/17/3/1231
9. https://link.springer.com/article/10.1007/s44187-024-00129-0
10. https://www.sciencedirect.com/science/article/pii/S0022474X20300539