Use of Low-Cost Devices for Water Activity Determination by Cottage Food Producers

The aim of this research is to determine if low-cost devices can be used to accurately and reproducibly measure water activity (a_w). Small-scale food producers, including those in the cottage food industry and start-up companies, need affordable devices to accurately measure the a_w of their food products. Water activity plays a critical role in food safety and quality, and products must meet a predefined legal requirement (a_w ≤ 0.85). In this project, devices ranging from <$100 to ∼$2000 were tested against four criteria: (1) robustness in a stress test; (2) reproducibility; (3) equilibration time; and (4) accuracy. The performance of the devices was investigated by measuring the water activity of six saturated salt solutions (0.11 < a_w < 0.94 at T = 22°C ± 1°C). Linear regression models were developed for each device and implemented in Excel to give corrected values ± standard deviations. For one of the types of low-cost devices, seven more devices were tested to determine consistency among devices from the same manufacturer and brand. Devices were found to be suitable for a_w measurements for food safety if the corrected values were consistently close to the actual a_w-values of the saturated salt solutions and if the maximum error was lower than 0.005 (ISO 18787). Of the seven types of low-cost devices tested, none strictly met all conditions, but four were found to be sufficiently close to allow for use by cottage food producers for directional testing, provided that samples are also sent for lab testing.