Applications of in-store drying in the grain industry in Southeast Asia

• National Postharvest Institute for Research and Extension, Philippines
• King Mongkuts Institute of Technology, Thailand
• University of Agriculture and Forestry, Vietnam

The ability to harvest crops during the wet season made possible by double-cropping, fertilisers and irrigation results in increased postharvest drying problems. This is particularly so in the humid tropics of Southeast Asia, where farmers and traders still rely on sun-drying or, occasionally, flat-bed drying. Rice and maize, the main cereal crops in the region, are especially prone to losses due to inadequate drying after harvest. In addition, particularly in maize, moist conditions favour the growth of moulds that produce mycotoxins (e.g. aflatoxins)a serious health threat for both humans and livestock.

There is clearly a need to extend satisfactory drying strategies for cereal grains into the small-scale private sector (traders, millers, farmers' cooperatives). This sector constitutes the bulk of the grain industry in the Philippines and Thailandthe two countries targeted in this project. At a later stage, in March 1994, Vietnam also became involved in the project.
Two previous ACIAR projects (PNs 8308 and 8608), led by a team from the University of New South Wales, developed adequate drying systems based on two-stage dryinga rapid initial stage to remove excess moisture, followed by slow in-store dryingfor large scale (>100 tonne) grain operations in the humid tropics. Small-scale operationsdefined as ones handling about 1 tonne of grain per hourwere not given much consideration. Problems that remain with small-scale systems concern deficiencies in existing designs leading to difficulties in operation, low efficiency, and high running costs combined with high capital cost.

This projectalso to be led by the University of New South Wales teamwill develop storage and drying methods based on second-stage in-store drying and investigate a range of alternatives for the first stage. The latter will include sun-drying, mobile flash drying, continuous flow drying and solar drying. The collaborators, working in Australia, the Philippines and Thailand, will evaluatewith regard to both economics and qualitythe integration of selected systems into the existing postharvest infrastructure. Their final objective will be to encourage the adoption of suitable drying systems.
Methodology, to be employed in the course of three subprojects, will include:

the determination of thermophysical properties of grain, collection of weather data for storage periods, and studies of mould growth and aflatoxin build-up under different drying conditions;
the development of computer models to suit each typical situation;and
the construction of prototypes.

The Australian team is experienced in adapting computer models of drying systems to solving particular problems within the Australian grain industry. It is also familiar with the problems associated with fissuring and stress cracking, which commonly occur in sun drying, where the rate of drying tends to be uncontrolled. Once the dryer systems model has been constructed and checked, several possible dryer scenarios will be developed and tested, using the model, for specific locations. The assessment in the field will include studies of drying efficiency, quality tests and detailed cost analysis.

The results of the mycological studies will provide data for a model of fungal growth and aflatoxin build-up at different stages of postharvest handling. As a result, strategies for appropriate drying will be elaborated.

Increased production of higher quality grain will reduce the need for grain imports to the Philippines, and will stimulate exports of grain from Thailand and Vietnam. The shift from using roads as sunning floors will have a beneficial effect on road transport. Improved nutritional quality of grain, particularly from crops now affected by aflatoxin, will result in reduced losses in livestock production and reduced exposure of humans to the carcinogenic effects of aflatoxins in maize-eating populations in the Philippines.

A study carried out in the Philippines over a period of 2 years showed a cost to benefit ratio of around 1:4.4 for a mechanical dryer used for paddy by a farmers' group. Mechanical drying has the potential to increase the chance that grain will rank in the higher grade categories. For rice in the Philippines five grades, A to E, are currently used. The most likely effects of the drying technologies resulting from this project are to upgrade C grade rice to A grade, or perhaps D to B. If this occurs, price gains will be of the order of $A4050/tonne.

The thermophysical data acquired in the project will be useful in further work in Australia aimed at designing drying equipment. In addition, the knowledge acquired in improving the quality of maize (aflatoxin control and reduction in stress cracks) could be valuable to the Australian industry and to Australian experts offering international consultancy services.