Using Relative Humidity Indicator Paper to Measure Seed and Commodity Moisture Contents

Core Ideas Low seed and commodity moisture contents are critical for safe storage. Equipment for measuring moisture content is often unavailable in rural locations. Commodity moisture content and equilibrium relative humidity are uniquely related. Relative humidity can be measured easily using electronic meters or indicator paper. Commodity moisture content can be conveniently measured using such indicator strips. Declines of seed viability in storage and losses of stored commodities due to fungal spoilage and insect pests are promoted by high moisture content. However, measuring seed or grain moisture content in the field can be difficult, particularly in rural locations in developing countries. Because seed/commodity moisture content is uniquely related to equilibrium relative humidity at a given temperature, moisture content can be estimated by measuring the relative humidity of a sample enclosed in a sealed container. Relative humidity can be measured using electronic meters, or even more inexpensively using indicator paper that changes color in response to relative humidity. We describe this method and provide a spreadsheet to convert relative humidity to moisture content for many common seeds and commodities. This simple method can be used in the field for quickly estimating seed or commodity moisture content to determine whether further drying is needed or is suitable for storage, milling or other uses.