There is no free water flowing in the solid fermentation medium, which is suitable for the growth of microorganisms with water activity of 0.93 ~ 0.98, which limits the application scope and the growth of some miscellaneous bacteria.

There is a gradient in nutrient concentration, uneven fermentation, uneven growth of bacteria, absorption of nutrients and secretion of metabolites.

In solid state fermentation, the contact area between culture medium and gas is large and oxygen supply is sufficient. At the same time, the resistance of air passing through the solid layer is small and the energy consumption is low.

Using solid raw materials, saccharification and fermentation are carried out at the same time in the fermentation process, which simplifies the operation process and saves energy consumption.

High substrate concentration can produce high product concentration.

Because of the high concentration of the product, the extraction process is simple and controllable, and a large amount of organic waste liquid will not be generated, but the extract contains substrate components.

The mechanization of production is low, and the process is difficult to control because of the lack of on-line sensing instruments.