Equilibrium moisture content (EMC) plays a fundamental role on the properties of bio-derived products such as food, waste biomass, seeds, and many others. For foods, the moisture content affects flavor, texture, and storing conditions. In other applications, moisture affects drying conditions and energy requirements for food processing. Adequate modeling of EMC in food products as

a function of the water activity is very important for designing and understanding food engineering processes

as well for process monitoring and control. Most models used to correlate EMC with water activity are based on traditional adsorption models which take into account the adsorption energy of water with the substrate only and

do not consider other non-adsorption interactions of water within the substrate such as mixing and swelling. Many other models are empirical, which are commonly used for interpolation. Although a detailed description of this type of substrate is very complex, we present a simple model based on standard molecular-thermodynamic models and

standard statistical mechanics formulations to correlate the EMC with water activity that attempts to consider both adsorption and non-adsorption interactions of the water with the food product. Although the model is basic, it captures the behavior of water in this type of systems fairly well and it can be used to fit experimental data with parameters that provide better physical insight on the nature of substrate or food product. We illustrate the capabilities of the model with two case studies for food products.