Solid State Fermentation vs. Submerged Fermentation — What's the Difference?

Solid State Fermentation (SSF) is a process where microorganisms grow on a solid substrate without the presence of free water. This method is akin to natural fermentation processes and is often used for products like enzymes, organic acids, and fermented foods. Submerged Fermentation (SmF), however, involves the cultivation of microorganisms in a liquid nutrient medium, where the substrate is dissolved or suspended in water.

In SSF, the solid substrate not only provides nutrients but also acts as a physical support for the growth of microorganisms. This method is efficient in terms of energy and water usage and often results in higher product concentrations. SmF allows for easier control and monitoring of the fermentation process, including parameters like pH, temperature, and oxygen levels, making it suitable for large-scale production.

SSF is typically used for the production of products like antibiotics, citric acid, and traditional fermented foods such as tempeh and soy sauce. It is favored for its lower risk of contamination and lower energy requirements. SmF is widely used in the pharmaceutical industry for the production of antibiotics, vaccines, and for wastewater treatment, due to its scalability and ease of product recovery.

The control of environmental conditions in SSF can be challenging due to the heterogeneity of the solid substrate. In contrast, SmF offers better control over fermentation conditions, making it more predictable and consistent. However, SmF typically requires more energy, especially for aeration and agitation, compared to SSF.

From an environmental standpoint, SSF is considered more sustainable, producing less wastewater and utilizing agricultural residues effectively. SmF, while requiring more resources, is more adaptable to a variety of industrial applications due to its ease of scaling and process control.