Low-Cost DIY Capacitive Sensor for Water Activity of Food Samples

Document Type

Conference Proceeding

Publication Date



Water activity of food products has been proven to be an important indicator in establishing food quality, mainly ensuring stability and safety. However, most commercial water activity meters are expensive and relatively inaccessible for micro-, small-and medium-sized enterprises (MSMEs). Thus, this study utilizes an off-the-shelf commercial relative humidity (RH) meter with a capacitive sensor that is relatively inexpensive and retrofitted it with 3D -printed casing and sample container to allow measurement of the equilibrium RH of a food sample. This is then calibrated to yield the water activity at room temperature (ca. 25C). The RH sensor shows a linear response to salt solution calibration standards and a sensitivity that can be corrected; the relative mean square error is ± 0.03. The calibrated DIY RH sensor was then tested for measurement of water activity of various food samples, wet and dry, with aw in the range of 0.20 to 0.90. Comparison of the results from the DIY RH sensor versus those of an analytical water activity meter (with a dew-point sensor) shows that the margin of error is ± 0.05. This would be good enough for estimating the water activity of food products especially for those that need to establish a cutoff for food safety of aw < 0.60. The DIY RH water activity sensor is also portable and will be a useful tool for point-of-use scenarios (such as in solar drying of food) and in resource-limited settings.