Water relations of solid state fermentation

International audience; The hydration level of the culture medium affects drastically the physiology of microorganisms. Thermodynamic properties of water in a solid-state medium such as water potential or water activity, and dynamic properties of water such as water diffusion are examined. The mechanisms of water transfer between intra and extracellular media are discussed, and different results on the incidence of the water activity level on the survival, growth and metabolism of microorganisms are reported. Optimal macroscopic and microscopic growth, or metabolic production by fungi occurs in media with water activity values lower than those of classical cultivation media (≈ 1). In solid …