There are two types of fermentation:

1. Submerged Liquid Fermentation
2. Solid State Fermentation

Submerged Liquid Fermentation (SLF)

• Submerged fermentation is an operation that involves the growth of microorganisms in a liquid broth or medium. 
• Liquid broth consists of nutrients and it results in the production & development of antibiotics, industrial enzymes or other products.
• The operation requires the uptake of specific microorganisms such as fungi and placing it in a small closed flask that contains the rich nutrient broth. 
• A high amount of oxygen is also needed for the process. When the fungi interact with the nutrients in the broth it results in the production of enzymes. As a result of improved fermentation technologies, at the industrial level (large scale) this production of yeasts has become the main yield (output) of microbiological industries.
• By using Fermenters the Fermentation is carried out in industries. Fermenters range from small 500ml Lab scale to large vessels which can store a large volume of the substrate.
• Microorganisms release or secrete enzymes or products of our interest in the selected medium (Extracellular Product) or store it inside their cell (Intracellular Product) 
• There are two most common methods by which submerged fermentation takes place; they are fed-batch fermentation and continuous fermentation. 

Solid State Fermentation (SSF)

• Solid State Fermentation is used in the production of pharmaceutical, food, fuel, and industrial products. 
• It is used as a substitute or as an alternative to submerged fermentation. In Japan, it is known as Koji fermentation and has existed for a long period of time. 
• In this process, we use microorganisms in a controlled environment to produce enzymes, fuel and nutrients. This fermentation is performed in the absence of free water by using Solid State Fermenter.
• It is a considerably simple process that requires a smaller amount of energy. It produces high volumetric productivity and it is similar (alike) to the natural environment of certain fungi. 
• This fermentation process includes solid matrix-like rice bran and substrate is created by placing it on a medium to alongside the microorganisms.
• This is then stored at a specific temperature, at the optimum temperature of the Microorganism, for one to five days. 
• Solid State Fermentation plays an important role in developing filamentous fungi. It allows air to come in contact with the mycelium by staining or smearing the mycelium. SSF allows the growth of filamentous fungi in conditions which represent their natural environment.

Sterilization of the environment is not necessarily needed when carrying out SSF, because the sterilization is initiated by fermentation substrate and the microorganisms prohibit or prevent microflora from growing. But nowadays for complex and advanced fermentation, Sterile Solid State Fermenters are also available.

Difference between Solid State Fermentation (SSF) and Submerged  Liquid Fermentation (SLF)

Solid State Fermentation (SSF)	Submerged  Liquid Fermentation (SLF)
Organisms that need less water for growth are preferred eg:- filamentous fungi.	Media concentration is very low as compared to water content.
Artificial or natural support, consisting of all components required for growth in the form of a solution.	Necessary processed ingredients are expensive.
Chances of contamination are less because of the low availability of water.	In SLF, higher water activity becomes the major cause of contamination.
In SSF, small-size fermenters can be used but it is entirely based on the process.	Large-scale fermenters & bioreactors are needed because media is highly diluted, but again volume depends upon the type of product and other limitations.
There is less utilization of energy for aeration and gas transfer.	More power is consumed because of high air pressure and there is the poor transfer of gas in SLF.
In SSF the diffusion of nutrients is a limiting factor for growth.	Diffusion becomes easy due to robust or strong mixing.
Presence of difficulties in the measurement of biomass quantity and other online processes.	The availability of online sensors and sampling is easy for biomass measurement.
Easy downstream processing, cheaper and time-saving.	The presence of water makes downstream processes difficult and highly expensive.
No liquid waste is produced.	They produce high quantities of liquid waste which causes difficulties in dumping.
Soluble Substrates (sugars) are used.	Polymer Insoluble Substrates, organic & inorganic media components, Starch Cellulose, Pectins, etc are used.