Title	Protecting grain quality at harvest & during storage
Description	Research Update for Growers - Northern Region - August / September 2003
Author	Alan Andrews Customvac Australia Pty Ltd Ph 07 4634 7344 customvac@customvac.com.au www.customvac.com.au Andrew Kotzur Modern Engineering & Construction Pty Ltd Ph 02 6029 4700 andrew@kotzur.com.au www.kotzur.com.au
Presented	Spring Ridge & Moree NSW; Biloela & Capella QLD

Take home message

• Stored grain is an investment of your time and money
• Harvesting early then aerating and drying (if needed) reduces harvest loss risks
• Managing moisture temperature and insects reduces stored grain quality losses
• Aeration provides grain quality drying & insect management opportunities
• Sealable storage delivers highly efficient insect control options
• Automatic controllers improve the efficiency & cost/benefit of aeration systems

Summary

The grain industry in Australia sacrifices millions of dollars each year to harvest and storage losses. But individual growers have the opportunity of using existing equipment and strategies to manage over-moisture grain protect stored-grain quality and control insect activity.

Tools for Protecting Grain Quality

Grain that remains in the field for extended periods is at greater risk of weather damage. Early harvest supported by aeration and drying reduces the risk of harvest loss - particularly in a wet season.

Poor management of temperature and moisture in stored grain results in moulding heating and insect activity. Aeration cooling aeration maintenance and fumigation in sealed storages are key weapons in protecting grain against the enemies of grain quality.

Early Harvest and Aeration

Starting your harvest early reduces the risk of field loss from weather damage and gives more management options. An early harvest does not necessarily mean handling large quantities of high moisture content grain. A strategy available every season is to start harvesting at marginal moisture levels (typically 2% to up to 3% high). This over-moisture grain is held under aeration then dried or blended to meet market requirements.

The benefits of an early harvest/aeration strategy include

• Gaining extra harvest hours each day
• Returning to the field faster after rain
• Blending dry & over-moisture grain
• Holding wet grain longer before drying
• Evening-out grain moisture & temperature
• Preventing moulds & sprouting in grain
• Reducing quality loss from weather damage

During a wet harvest the weather controls many decisions. But well-planned aeration drying and storage systems dramatically reduce the risk of grain loss.

Aeration - More Than Cool Air

Cooling grain is only one beneficial function of aeration. The variety of equipment & purposes can be conveniently grouped under 3 distinct categories namely

• Aeration-Maintenance (selecting air to maintain grain quality)
• Aeration-Cooling (selecting air to cool grain quickly)
• Aeration-Drying (selecting air to remove moisture from grain)

The key difference between the 3 categories is the QUANTITY and QUALITY of aeration air needed to achieve a desired result. Aeration-drying typically uses 10 to 15 times the air-flow suitable for aeration-cooling. The attached graph gives an indication of the wide variation in air-flows between the different aeration categories.

Aeration-Cooling & Maintenance

Aeration-cooling & maintenance systems reduce the grain bulk temperature to lower than average air temperature. Over time they also create even conditions throughout the grain mass. The wide range of quality-related benefits includes

• storing damp grain safely for longer periods
• avoiding 'hot spots' condensation & caking
• maintaining seed/malting barley viability
• protecting milling properties
• suppressing grain insect activity
• avoiding chemical residues
• inhibiting moulding & sprouting
• preserving colour and oil quality

Moisture damage in stored grain is often blamed on leaky silos. But a more common cause is moisture concentration as a result of uneven temperature profiles throughout the grain mass.

The effect is not restricted to high moisture grain. 'Dry' grain also has plenty of moisture available to move around. Aeration cooling & maintenance is particularly effective in controlling moisture damage in stored grain.

High-Speed Dryers

High performance continuous and batch dryers remove moisture in a way that is predictable and reliable. These dryers need high air-flows. For example a continuous flow dryer may use around 40 times the air flow used in typical aeration-drying systems. They also depend on high heat input to achieve rapid and reliable drying.

Aeration-Drying (no added heat)

Purpose-designed aeration-drying systems provide opportunities to remove moisture from grain bulks at lower capital & operating cost than high-speed dryers. They add significant flexibility to a harvest system and are predictable in terms of what can be achieved under certain grain and weather conditions. A desired result can however be difficult to obtain under adverse weather conditions.

Moisture removal rates are relatively slow (days to weeks) and depend on availability of suitable drying air for extended periods. The system is most reliable when managing small batches of marginal-moisture grain as part of an early-harvest strategy.

During wet harvests (when drying is needed most) aeration-drying delivers lower performance. Under these conditions great care is needed to avoid quality loss caused by holding grain for extended periods at high temperature and moisture. If drying stalls due to adverse weather it may be necessary to operate under aeration- cooling to protect grain until conditions are more favourable for drying. Some systems allow for supplementary heating of air.

Efficient aeration-drying typically needs 10 to 15 times the air-flow rate used for aeration-cooling. These higher flows mean that fans must be capable of operating at higher pressure than in most cooling/maintenance systems.

Operators of aeration-cooling & maintenance systems sometimes claim remarkable drying performance. Although limited drying can occur under certain air/grain conditions this apparent drying effect is more likely due to other processes.

An 'illusion of drying' can be created by moisture transfer ('equalising') between wetter and drier grains in combination with free-moisture removal from the surface areas of grain kernels. This effect is worthwhile in managing variable moisture in grain loaded into storage particularly in an early harvest strategy. But beware of confusing it with grain drying.

Aeration Control

The efficiency and performance of any aeration system is directly related to the way it is operated. In-field experience shows that correctly operated aeration controllers offer significant benefit over manual control.

Aeration controllers take the guess-work out of selecting air best suited to the operation i.e. Aeration Drying Aeration Cooling or Aeration Maintenance.

Aeration-Cooling & Maintenance Controllers allow marginal moisture management at harvest and protect grain quality during longer-term storage. They do this by maintaining cool even conditions through-out the grain mass. The most effective units use a combination of air temperature and humidity to select the best available air and to provide additional protection against moisture addition.

Aeration-Drying Controllers select air to purpose-built (high air-flow per tonne) aeration-drying systems. These controllers do not suit cooling and maintenance applications.

Most controllers used in Australia do not include cooling/maintenance and drying functions in the one unit. More sophisticated controllers are under development but their cost and extra management requirement may limit their application to larger storage systems.

Managing Insects with Aeration

Some growers use aeration as their primary insect management method. This is possible because aeration modifies temperature moisture and air movement in a grain mass.

The result is an environment that deters insects from entering an aerated grain mass and dramatically reduces their activity if they are present. Insect activity in clean storage systems using correctly controlled aeration can be maintained at very low levels.

Major infestations of insects in aerated grain are usually a result of poor system design incorrect control or poor grain hygiene practices.

It is however important to understand that aeration systems operating in most parts of Australia will not create conditions that kill stored grain insects. The effect of temperature on stored grain insects can be generalised as follows

• Above 35° High temperatures limit growth
• 25° - 35° Optimum insect population growth
• 15° - 25° Activity reduces as temperature drops
• 10° - 15° Population growth very slow
• 0° - 10° No population growth/eventual death
• Below 0° Faster kill of stored grain insects
  (Note that these temperature effects are a general guide only and will vary between insect species)

Aeration does not guarantee that there will be no live insects in stored grain. Our harvest/climate pattern is significantly different to other areas of the world where aeration may be adequate to meet 'nil insect tolerance'.

An integrated approach using aeration for grain quality management and sealed storage for highly effective insect control will deliver low risk for most operators.

Sealable Silos for Insect Control

Sealed Silos offer reliable and low cost insect pest control. They also offer the added benefit of being able to treat grain without the risk of leaving unacceptable chemical residues.

A correctly sealed silo maintains high levels of fumigant inside the silo for long periods of time. This ensures that all stages of the insect life cycle are killed resulting in insect-free grain.

Using fumigants in unsealed silos will not kill the early stages of the insect life cycle and there is a significant risk of encouraging insect resistance to fumigation.

Most current practice involves use of Phosphine formulations (in tablet or blanket form) for fumigation. It is important that such a treatment be limited to properly sealed structures as increasing levels of resistance are a major threat to one of our last weapons in the insect war.

Certain applications suit the use of 'trickle-flow' fumigation systems. These are less common than fumigation in fully sealed structures and require higher levels of design cost and operator management.

At present the higher cost of Controlled Atmosphere (CA) systems using nitrogen or carbon dioxide limits their use to specialist applications including storage of organic grains.

The Future

Many market forces and technological changes will affect future grain storage practices on farms. Included amongst these are

• Increased storage of grain on farms
• Wider use of aeration & drying in harvest management
• Continued demand for grain free of chemical residues
• Increased use of sealed storage & fumigants to control insects
• Tighter grain quality standards required by markets
• Increased application of aeration to protect grain quality
• Wider use of controllers to increase aeration efficiency

Australia's grain production and marketing future presents challenges and opportunities for growers. Investment in efficient grain quality management practices will increase the likelihood of profitable returns.

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How much Air do I need?

Different quantities and 'qualities' of air are needed to achieve specific aeration results.

Typical Air-flow Rates for different aeration functions are shown in the graph

1. Aeration-Maintenance
2. Aeration-Cooling
3. Aeration-Drying

Graph supplied by Customvac Australia Pty Ltd

Remember -
The effectiveness of Aeration Maintenance Cooling or Drying is not determined by air QUANTITY alone. Aeration must also take into account the air temperature and relative humidity grain type and moisture content and intended final use of grain.