Problems in Solid Substrate Fermentation - The koji or solid substrate fermentation processes present the following difficulties:
(i) they are difficult to scale up,

(ii) it is difficult to monitor and control the various factors, e.g., pH, temperature, nutrient distribution, etc., during the process,

(iii) gas exchange, i.e., O2 supply and removal of CO2 presents problems, and
(iv) heat transfer and removal are not as easy and efficient as with liquid fermenters. However,

(i) the fermentation systems are low cost and simple devices and

(ii) their power requirement is very low.