Near Infrared (NIR) Reflectance

Near infrared reflectance and transmittance are indirect methods of determining the moisture content of materials. The moisture content is correlated to the reflectance of electromagnetic radiation at specific wavelengths. Near infrared is the region between 700 and 2500 nm. Transmittance uses shorter wavelengths (900 - 1200 nm) while reflectance uses longer wavelengths (1200 - 2500 nm).

NIR devices have a major advantage in that they are capable of simultaneously measuring other components. For example, NIR transmittance can be used to measure the moisture content, protein and fat contents, and soluble solids. However, the purchase price of such devices is relatively high.

Problems with NIR reflectance devices include their sensitivity to the following: uneven moisture distribution within particles, variations in particle size distribution, and variations in color. NIR transmittance may also be sensitive to the presence of components other than water. Changes in such parameters require that the NIR device be recalibrated in order to attain accurate readings.