In the batch fermentation process, the entire medium is removed from the fermentation vessel. The vessel is then thoroughly washed, cleaned and the new batch is started only thereafter. The bioreactor is initially loaded with fresh medium and inoculated with selected microorganism.

During the batch fermentation process, various physiological states of the microorganism

are observed (Figure 3):

a. Lag phase — Period where microorganisms adapt to the new environment.

b. Positive acceleration phase — Period of slow increase in the population

c. Logarithmic or exponential phase — Period of rapid rise in population due to availability of nutrients. The exponential phase may be described by the following equation:

dX/dt = Vх

Where x is the concentration of microbial biomass

t is time, in hours

and p is the specific growth rate in hours-1

d. Negative acceleration phase — Period in which there is a slow rise in population as the environmental resistance increases.

e. Stationary phase — Finally, growth rate becomes stable because mortality and natality rates become equal. During the stationary phase, the organism is still maintaining a certain metabolic activity, while some secondary metabolites are formed (products not associated with microbial growth).

f. Death phase — Finally, environmental stress causes a decrease in metabolic activity of yeast and autolysis.