Working Principle and Operating Steps of Grain Moisture Analyzers

1. Overview of Grain Moisture Analyzers:

The moisture content of grain, cereals and oilseeds is the percentage of water mass relative to sample mass. Moisture is the most fundamental test item in evaluating grain and oilseed quality. Its determination is of great significance for safe storage, processing, and purchasing, sales and allocation. The moisture content of sound grain and oilseeds always falls within a certain range.

However, maturity, harvest timing and climatic conditions (temperature, humidity) make moisture content a variable. Proper moisture is needed in storage; excessive moisture not only wastes storage capacity but also promotes kernel sprouting, heating and spoilage of the grain mass, growth of microorganisms and pests, and loss of valuable substances in the kernels. In processing, every step imposes moisture requirements on raw materials, semi-finished and finished products; moisture outside process requirements affects product quality, reduces yield and increases power consumption.

2. Moisture in Grain:

Due to grain's equilibrium moisture, air humidity in the warehouse and in the pores of the grain mass greatly affects grain moisture. Air humidity affects warehouse humidity, which affects grain-mass humidity; air humidity, warehouse humidity, grain-mass humidity and grain moisture content together determine changes in grain moisture. Apart from roof leaks and seepage through walls and floors, all moisture changes after storage are caused by changes in air humidity.

Annual changes in grain moisture follow annual changes in relative humidity with regional differences: in northern regions humidity is low in summer and high in winter; in coastal regions it is low in autumn and high in spring. Overall, moisture changes in the surface and outer layers of stored grain are mainly affected by external and warehouse humidity, while internal changes are more complex. Except for the upper layer, annual moisture changes in the middle and lower layers are small—within1%. Accordingly, seal the warehouse when outside humidity is high to prevent moisture absorption, and ventilate when outside humidity is low and temperature is cool. Grain whose surface has absorbed moisture or whose upper layer is high in moisture can be turned to release moisture.

In general composition analysis of grain and oilseeds, protein, lipids, carbohydrates and ash are approximate basic components

, whereas moisture analysis targets the well-defined water moleculeH2O. A method that measures moisture accurately, simply and rapidly is therefore highly desirable. Over the years, new technologies have continually been applied to develop fast, accurate methods for various grains and oilseeds. Yet accurately determining moisture is no easy task, and many problems remain to be solved.

3. Methods for Determining Grain Moisture:

Grain moisture and storage humidity reflect interdependent levels within the stored-grain ecosystem and are crucial to the succession of the entire grain-storage biological community. When grain moisture is low, the life activities of grain and microorganisms are suppressed and safe storage is ensured. But once moisture rises to a suitable level, microorganisms escape natural control and develop rapidly, causing mold in severe cases.

Although the dry environment created by low-moisture grain cannot completely rule out insect and mite activity, some species cannot survive because the dry conditions destroy their physiological balance. Even surviving populations reproduce less due to"water shortage", making population growth difficult and the whole system extremely unstable. Any form of water addition or humidification may trigger a pest-population outbreak in a short time; strict control of grain moisture change is therefore a key measure for safe storage. Moisture change during storage is closely tied to storage safety, and grain moisture directly reflects grain safety and stability—so moisture must be monitored during storage. Current research and practice show that humidity-sensitive resistors are the main components for electronic, automated in-bin grain-moisture detection, but existing humidity resistors have narrow ranges, serious hysteresis, poor linearity, slow response, marked environmental-humidity influence and large detection errors—especially at low moisture. Thus electronic, automated in-bin detection has not yet been realized. For online detection, however, the limited number of sensors required allows higher-precision, higher-priced components such as integrated circuits, and preliminary online grain-moisture detection has been achieved. At present, moisture during storage is mainly tested by sampling grain at designated points per regulations and measuring it in the laboratory; at procurement sites, rapid moisture analyzers or sensory testing are common; and advanced online detection technology is used during grain in/out operations.

During storage, safe grain is tested quarterly1–2 times; semi-safe grain at least once a month; hazardous grain whenever circumstances require. Localized moisture checks should be part of daily work, sampling spots prone to moisture absorption, condensation or abnormal temperature rise. If kernels show damp surfaces, reduced hardness or poorer flowability, sample and test immediately.