ARS | Publication request: Microwave Moisture Meter for Rapid and Nondestructive Grading of Peanuts

Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: May 14, 2010
Publication Date: June 20, 2010
Citation: ASABE Paper No. 1008521, American Society of Agricultural and Biological Engineers, ST. Jopseph, MI. 2010.

Interpretive Summary: Electrical characteristics, known as dielectric properties, of grain and oilseed are closely related to the amount of water that they contain. Consequently, instruments can be designed to sense these dielectric properties and be calibrated to read moisture content. Such instruments, called moisture meters, are widely used in the grain and seed trade for rapid determination of moisture content. Moisture content is especially important in the sale and storage of peanuts so that spoilage and development of toxins can be avoided. If kernel moisture contents of peanut lots exceed 10.49 percent, they cannot be sold and have to be dried before they can be reconsidered for sale. Research on microwave dielectric properties of peanuts has revealed that measurements at these higher frequencies can reliably measure the moisture content of the peanut kernels from measurements on the unshelled peanut pods. This paper describes a low-cost microwave moisture meter built with off-the-shelf components that rapidly and nondestructively determines the kernel moisture content from measurements on unshelled peanut pods. At peanut buying points, samples go through a thorough grading process before the moisture content is determined, and at that time the decision is made as to whether the peanut lot can be sold. Thus, the new microwave moisture technique offers a real advantage in peanut grading operations, because moisture content can be determined at the beginning of the grading process, and if it is too high, the time and labor lost in grading those samples can be avoided. The new microwave moisture sensor offers promise for improving efficiencies of grading and processing as well as preventing losses due to spoilage and will be a useful tool for peanut farmers, handlers, and processors, thus providing safe and high quality products for consumers.

Technical Abstract: A low-cost microwave moisture meter made with off-the-shelf components was developed, calibrated and tested in the laboratory and in the field for the grading of peanuts. The meter allows rapid and nondestructive determination of kernel moisture content from measurements on unshelled peanut pods. The meter operates at a frequency of 5.8 GHz and uses the principle of free-space transmission measurement of the dielectric properties. Moisture content is determined independent of bulk density with a permittivity-based algorithm. Besides kernel moisture content, the meter provides simultaneously, from the same set of dielectric measurements, the bulk density and moisture content of the peanut pods.