Grain that is stored moist may colour or crack or grow moulds which produce aflatoxins or ergosterol, lowering grain quality, millability and value. Paddy-grown rice in subtropical southern China is harvested in the wet season, when the grain is above 18% moisture by weight. Maize in the short-growing season areas of northeastern China is often harvested at 25-35% moisture, to avoid the severe winter frosts. The harvest is dried on sunning floors if possible, but constrained by poor weather and lack of space. While major investments have been made in grain storage facilities for China in the last decade, the need for strategies to manage intake moisture content and optimise quality of stored grains remains.
Annually, the Chinese government procures about a third of the grain harvest at a fixed price as payment for rent and tax. The maize and rice are assessed by the grain-handling bureaus' first-line depots, and then passed on to larger depots which dry some of the grain in coal-fired column dryers or mechanical dryers, ready for distribution; the rest is stored and sun-dried during spring and summer the following year. The maize may freeze into a mass, which complicates its handling until the thaw.
This project aimed to design safe grain-drying systems that overcame the problems caused by storage of wet grain - mize in northeastern China and rice in its subtropical southern region.
This project capitalised on earlier ACIAR funded research in Southeast Asia. The Australian scientists worked with researchers, grain authorities and manufacturers of drying equipment to develop and implement drying systems that optimise energy efficiency and reduce damage and mouldiness of treated grain. A key element of the project was the use of grain storage facilities as the test sites of the drying systems, with links to local equipment manufacturers who could produce the technology needed for wider implementation of successful strategies.
Project staff assembled data on economics, weather and grain handling. The data formed the context for computer models of the effects of various drying systems on grain quality and efficiency of grain handling. On the basis of model results, project staff designed and tested specific drying systems with technical and economic characteristics to suit the various grain-handling depots. Following this they tested the systems at commercial scale and educated all users, by extension and training.
The Australian researchers applied current cereal technology and microbiological techniques in the laboratory to measure the effects of drying at sub-zero temperatures on cracking, on grain colour and viability, and on the production of fungal toxins. Meanwhile collaborators from the grain-handling bureaus in China gathered details of weather conditions for the past 10 years or more, annual grain yields and volumes involved in storage, capital and energy costs, details of quality changes under given storage conditions, and end-user needs.
The project partners developed and tested computer simulations of drying processes for maize and paddy, based on information gained on the thermophysical properties of grains, local weather data and parameters of the storage/drying systems in grain depots. These computer simulations were used to design prototypes, compare drying strategies, optimize processing and also for the development of automatic control systems for field testing in China.
For two seasons the researchers trialled drying systems at key sites near Zhaodong in Heilongjiang (maize) and near Zhangjiagang in Jiangsu (rice). Good progress was made in the implementation of two-stage grain drying systems both for rice in the southern and maize in northeastern provinces. A number of trials were conducted in aerated warehouses. Automatic control systems developed by the project team significantly improved the performance of the systems by reducing the drying cost to that of sun drying.
As a result of the work, and with further data collection and fine-tuning of models and systems, optimum technical and economic options could be proposed for in-store drying of grain in various agri-climatic regions of China. Also studies on fundamental aspects of heat and mass transfer during drying, especially at low temperature, are providing valuable information for process optimisation with possible spin-off for the Australian food industry.
In-store drying research led to more reliable improvements in the quality of paddy and maize, superior to the quality obtained with high-temperature drying systems. In view of the potential benefits to be obtained through wider use of the technology for in-store drying of rice, the Chinese decided to establish some demonstration sites for paddy drying in Heilongjiang province (the project had concentrated on maize drying at one demonstration site).
Noting that there was potential for a very high level of impact from this project, the project review panel recommended a project extension to promote the wider implementation of technologies. This involved continuing to strengthen links with industry, development of appropriate training modules and capacity building in China to undertake the more theoretical elements of modelling and system design for grain drying. The extension also enabled completion of the economic analysis of the drying systems, a process critical to successful implementation.
Links:
[1] http://www.aciar.gov.au/country/China
[2] http://www.aciar.gov.au/programarea/Horticulture