Moisture content: What is it and how can it be measured?

Dependence on water is pervasive in agriculture, affecting growth, harvesting, processing and storage of the products of the land. A great many sensors exist for measurement of water distribution, flow and quality, but we focus here on the water content of produce. Moisture content (M.C.) is a key parameter affecting the properties of commercially important products such as foods, cellulosics (e.g. wood products), textiles and a host of other miscellaneous materials. The common understanding of “moisture content” is the water content of a material, usually a solid such as wood or bread. But behind this apparent simplicity lies surprising complexity. The question, “What is moisture content and what are our sensors measuring?” is not easily answered, and there exists a plethora of different, commonly incompatible, measurement methods. In this paper we examine the strengths and weaknesses of some common commercial and laboratory measurement methods and then focus on the prospects for a universal physical definition of moisture content so that sensors can be tailored to give results most pertinent to the produce being measured.