BIOLOGY Volume 2 - A Guide to General Biology - 2004
12. MICROBIOLOGY AND BIOTECHNOLOGY
12.10. Large-scale production
12.10.5. Batch, fed-batch and continuous culture
There are two primary Types of Fermentation: batch fermentation (or a closed system) and continuous culture (or an open system). In batch fermentation, all necessary ingredients are added before the process begins; during cultivation, no nutrients are added and the fermentation parameters remain unchanged. This is precisely why it is referred to as a closed system. Once a sufficient amount of product has been formed, the process is stopped. The Contents of the fermenter are then harvested, the product is extracted, the spent microorganisms are discarded, and the fermenter is cleaned and prepared for a new batch.
Continuous culture is an ongoing, long-term operation lasting many weeks, during which nutrients are added to the medium as they are consumed, and excess culture is continuously withdrawn. Although this setup closely mirrors natural conditions—such as those in the gut—continuous culture has relatively limited Applications. For instance, ICI used this approach to produce Single-Cell Protein known as pruteen from the bacterium Methylophilusmethylotrophus (section 12.12.3). The fermenter operated continuously for 100 days, achieving a productivity of 150 tonnes per day.
While continuous culture is not yet widely used, fed-batch cultivation is becoming increasingly popular as a compromise between the two systems. Fed-batch cultivation offers a more controllable process compared to traditional batch culture. The growth phase is extended by feeding nutrients at low concentrations throughout the fermentation process rather than adding them all at once at the start. One of the main advantages of this method is The ability to regulate the growth rate and match it to the oxygen supply rate. This process is commonly used in the commercial production of baker's Yeast. If too much sugar is added to yeast Cells, they shift to Anaerobic Respiration and produce alcohol instead of biomass. Fed-batch culture is also utilized in The production of penicillin (section 12.11.1).
The Advantages and disadvantages of batch and continuous culture are summarized in Table 12.4.
Class="center">Table 12.4. Advantages and disadvantages of batch and continuous culture
Advantages |
Disadvantages |
|
Batch culture |
Used for secondary metabolites whose production is not linked to growth, such as Antibiotics Can utilize strains that are too unstable for continuous culture Easier to set up and start up than continuous culture Fermenters are less specialized and can be adapted for other processes depending on requirements |
Downtime between batches represents lost productive time Conditions within the fermenter change constantly during the process. Nutrients are depleted and the product accumulates. Heat output, acid or alkali production, and oxygen uptake all increase. Consequently, conditions gradually become unfavorable, and the growth rate steadily declines. See the graph in Fig. 12.8 |
Continuous culture |
More controllable. The goal is to maintain a constant environment. Nutrients are added as they are consumed, and product is removed as it accumulates Higher productivity due to the absence of downtime (continuous operation). This justifies the higher operational costs in certain scenarios The optimal (maximum or exponential) growth rate achieved is sustained indefinitely Smaller fermenters can be used since product output is higher Better suited for biomass production. Also used for producing ethanol, where synthesis is proportional to the growth rate Labor demands are more consistent and regular |
Higher risk of contamination, although this can be mitigated with good design More complex control systems required When applied to brewing, product yield increased, but product quality deteriorated |
Last update: 06/08/2026
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