In continuous fermentation, sterile nutrient medium is added to the fermenter continuously, and culture (containing cells and product) is removed at the same rate. The volume in the fermenter stays constant.Because fresh nutrients keep arriving and waste products keep being removed, the microorganisms are held in the log (exponential) phase of growth for a long time, often weeks. The culture never reaches the stationary phase.Continuous fermentation is therefore used to make primary metabolites: substances produced during normal growth, such as amino acids, ethanol and some enzymes, and to produce biomass itself. Mycoprotein (single-cell protein from Fusarium venenatum) is produced by continuous fermentation.Advantages
• Growth rate and productivity are high, because the cells are always in the log phase.
• There is little down time, as the fermenter does not need emptying and cleaning between batches.
• A smaller fermenter can give the same yield as a larger batch vessel.Disadvantages
• Conditions (temperature, pH, nutrient concentration, oxygen) are harder to keep constant over a long run.
• If contamination occurs, a very large amount of product is lost.
• It is not suitable for secondary metabolites, because the culture is never allowed to reach the stationary phase.
• The equipment is more complex and expensive to set up.
• Growth rate and productivity are high, because the cells are always in the log phase.
• There is little down time, as the fermenter does not need emptying and cleaning between batches.
• A smaller fermenter can give the same yield as a larger batch vessel.Disadvantages
• Conditions (temperature, pH, nutrient concentration, oxygen) are harder to keep constant over a long run.
• If contamination occurs, a very large amount of product is lost.
• It is not suitable for secondary metabolites, because the culture is never allowed to reach the stationary phase.
• The equipment is more complex and expensive to set up.