ABSTRACT
The main characteristics of solid-state fermentation (SSF) are the involvement of a solid matrix which could be either the nutrient substrate itself or a support impregnated with the nutrient medium, and the very low moisture content which makes this type of process suitable for a limited number of microorganisms. SSF resembles the natural habitat of microorganisms and reproduces natural microbiological processes like composting and ensiling. SSF is known since ancient times and it has been used extensively in the production of fermented foods. Fermentation processes are the most commonly used method in the production of organic acid and is globally dominated by submerged fermentation (SmF). Comparisons between SSF and SmF systems can be found in the literature but they are general and effective mostly on a laboratory scale. Citric Acid (CA) is the most important organic acid produced at industrial level and the world's second largest fermentation product produced after industrial ethanol.
