The drying in bulk storage of high-moisture grains in tropical climates-principles and application technology

• King Mongkuts Institute of Technology, Thailand
• Malaysian Agricultural Research and Development Institute, Malaysia
• National Postharvest Institute for Research and Extension, Philippines
• Universiti Pertanian Malaysia, Malaysia
• National Paddy and Rice Authority, Malaysia

Severe postharvest losses os stored grain occur in tropical climates, where high temperatures and humilities lead to rapid grain deterioration. Dryingthe most effective method of preservationis widely used to protect grain, but timing and methods of drying vary considerably.
The University of New South Wales and Ricegrowers' Co-operative Mills Ltd have developed and applied techniques for drying paddy rice in bulk stores in Australia. This project will continue that development and apply it to the drying of grain in bulk storage in tropical climates. Specific aspects will include studies: on the movement of moisture and temperature profiles through bulk-stored grain when aerated and dried under different conditions; on how various aeration and drying strategies affect grain quality; and on possible energy sources (burning the rice hulls, solar energy, etc) as means of improving drying. Scientists will also measure basic thermophysical data for paddy and other grains relevant to the design of bulk storage and drying facilities for tropical climates. Field trials in Australia, Malaysia and the Philippines will test procedures developed in the project.
Research on principles at the University of New South Wales will seek to develop a theory to describe the behaviour of stored grain when dried by aeration, and will require computer simulation studies using data from pilot plant and field trials. Regional research teams, who will carry out these trials under various tropical conditions, will first study the needs of particular regions and the potential for in-store drying using ambient aeration. This will involve information on ambient conditions, equilibrium data (on moisture and relative humidity) for local varieties, variations in grain moisture, maturity and quality at harvest and the resources (energy, storage facilities, etc.) and expectations of potential users of the system.
At this stage, all team members will consult together to discuss methods of in-store drying likely to be successful in the different countries and to plan the regional pilot plant studies. After designing and building pilot driers, the regional scientists will use them to dry paddy rice. A detailed analysis of the date these trials provide will then follow in Australia, and should indicate the likely success of in-store drying and whether or not supplemental heating is necessary. If so, a study of indigenous energy sources will begin.
Field trials will use existing grain storages in Australia, Malaysia the Philippines and Thailand to dry moist grain, and will include measurements of the changes that occur in grain temperature and moisture content at various positions in the storage.
The Co-operative will be responsible for applying the principles above and testing them under field conditions in all four regions. Initial research will evaluate the effects of various strategies on the quality of paddy rice stored after field, hot-air or ambient drying. Each dried sample will be evaluated for ease of milling, grain cracking and breakage, grain colour, microbial build-up and cooking quality. A number of pilot bins with variable air-flow rate, air temperature and absolute humidity will facilitate study of the different techniques.
Automatic aeration controllers, developed under a joint program between the University and the Co-operative, have proved most effective in commercial operation. A modified controller will probably be essential in tropical climates, and the Co-operative's technical staff will design and build an appropriate model. Subject to successful trials, first in a pilot bin and then in a commercial rice storage, they will build three more controllers for field trials in bulk storages in each region.
In developing in-store drying methods that reduce and maximise quality, the project should also allow multiple use of facilities to store a range of grains, such as paddy rice, maize and legumes, at different times of year. Moveover, the basic knowledge of the characteristics of grain bulks, and of the movement of moisture and temperature profiles through grain during drying, will allow application of the technology to drying and storage in all tropical countries.