Drying processes of alfalfa green biomass (review)

Review examines the dehydration processes of alfalfa (Medicago sativa L.) green biomass, driven by the necessity to reduce its initial moisture content (70–80%) to levels 12–15% to prevent nutrient losses. The objective is to summarize and analyze the moisture transfer regularities in alfalfa tissues for the development of energy-efficient drying technologies. The review methodology is based on a systematic analysis of scientific literature (2015–2025) from eLIBRARY, Google Scholar, and ScienceDirect databases following the PRISMA-ScR protocol. The paper discusses the forms of water present in alfalfa: free water (85–90%), physicochemically bound water (10–15%) and chemically bound water, which determine the energy requirements of the dehydration process. The mechanisms of moisture transfer during the physiological (up to 40% moisture) and biochemical (40–15%) stages are analyzed, including intercellular, intracellular, and transmembrane diffusion. Three kinetic drying periods are identified: the constant rate period (free water evaporation) and two falling rate periods (bound water removal). Particular attention is given to the problem of asynchronous drying of leaves and stems, which leads to overdrying of leaves and degradation of nutrients. Addressing this issue requires preliminary mechanical treatment of the stems to equalize drying kinetics, as well as the selection of adaptive drying regimes. The development of mathematical modeling of the drying process is analyzed – from empirical thin-layer models to comprehensive diffusion models of coupled heat and mass transfer adapted for drying equipment. The prospect of integrating artificial intelligence and CFD modeling to optimize drying regimes while preserving leaf fraction quality is highlighted.