Submerged fermentation (SmF) is the classical fermentation type that has been used since the 1940s
[7]. In this technique, microorganisms grow in a liquid medium containing the needed nutrients. The quantity of water available for bacterial growth affects the development of biomass, metabolic reactions, and mass transfer processes
[8]. The free-flowing liquid substrates can be either a synthetic media (broths), a waste, or industrial by-product substrate such as molasses. It is noteworthy that this technique is suitable for microorganisms that usually require high moisture content and for the production of secondary metabolites that need to be used in their liquid form since they are usually secreted in the fermentation broth
[9]. Due to the numerous advantages of this technique, it is being used by many industries and facilities. Particularly, most of the enzyme-producing facilities use SmF due to better monitoring and ease of handling
[10]. Additionally, this technique allows for the precise control of important growth parameters, including temperature, pH, dissolved oxygen, and substrate concentration
[11]. SmF is also characterized by its simple downstream processing after fermentation, particularly easy purification of the products
[9][12]. This type of fermentation is less susceptible to substrate inhibition compared to other types, hence leading to a high product yield
[13]. Scale-up methods and bioreactors for this type of fermentation were well developed; thus, SmF can be used on an industrial scale
[14]. SmF supports the use of genetically modified organisms
[9]. On the other hand, however, it has various disadvantages. For one, it is a time-consuming process where secondary metabolites require time to be produced. Also, it is an energy-consuming process, since SmF is prone to bacterial and fungal contamination, and requires energy for sterilization. It is a costly process when synthetic media is used as a substrate and expensive raw materials are added to it. Finally, substrates in SmF are utilized quite rapidly and need to be constantly supplemented with nutrients or replaced
[15]. Like any other technique, SmF displays advantages and disadvantages, and its usage depends on the field of application and aim of the experiment
[7].