There are three types of fermentation processes and they are

  1. Batch fermentation
  2. Continuous fermentation
  3. Dual or multiple fermentation
  1. Batch fermentation

Batch fermentation is carried out in batches. Here, fermentation media is filled up to 80% space by fermentor, and the remaining space is used as head space. Head space plays an important role as some area of a fermentor is required for collection of air, gases, and foam which is produced during the fermentation process. Further, after inoculation of media the fermentor is steam sterilized and after sterilization, the nutrient media is cooled and inoculated with desired volume of inoculums under aseptic condition.

Fermentation process is carried out under optimum growth condition. It is stopped after specific period of time and the fermented media or broth are removed from the fermentor and the desired product is obtained.

The product obtained is passed through recovery and purification process. Later, the fermentor is cleaned and reused for the next batch. In this process, as the fermentation proceeds, the quantity of nutrients from the media gets depleted, and microbes and products increase. In batch fermentation, growth of micro-organism is slower down due to decrease of nutrients.

Advantages of batch fermentation

It requires less space, there are fewer chances of contamination and this process is easy to handle. The disadvantage is that it is a time consuming process and it requires more time for cleaning, sterilization, cooling. The yield of the product is also low.

  1. Continuous fermentation process.

In continous fermentation process fermentation runs continuously without emptying of fermentation tank. It involves continous addition of fresh media and withdrawal of fermentation product is constant.Each and every cell in fermentation media should be in log phase and not in stationary phase.The rate of addition of media should satisfy nutrient requirement of fermentation organism if rate of addition of media is slow there are chances that cells enter in stationary phase.There are three types of continuous fermentation processes.

i] Single stage continuous fermentation

ii] Single stage recycle continuous fermentation

iii] Multi-stage continuous fermentation

A] Single stage continuous fermentation

In Single stage Continuous Fermentation, the fermentor is used continuously. In this process, media is added at a specific rate as well as the product formed is removed at the same rate. The input of media and output of fermented media is balanced.

B] Single stage recycle continuous fermentation.

In Single stage Recycle Continuous Fermentation, a single fermentor is used continuously. The rate of inoculation of fermentation media and the rate of withdrawal of fermented broth is same. In this process, a portion of fermented broth plus withdrawal culture is recycled to the fermentor.

C] Multi-stage continuous fermentation.

In Multi-stage Continuous Fermentation process, two or more fermentors are operated continuously in sequence. In this fermentation process first fermentor is used for growth of cells because in some fermentation process the product is formed after cell multiplication. Here effluent of first fermentor acts as in-fluent for next fermentor.

The continuous fermentation techniques are operated by two operating systems that are chemostsat and turbidostat

Advantages of Continuous Fermentation process

  1. Product is formed continuously.
  2. Good product yield is obtained.
  3. The inoculation of culture is carried only once.
  4. Continuous fermentation process save time and labour work.

Disadvantages of Continuous Fermentation process

  1. This process is a bit complicated and difficult to operate.
  2. There are more chances of contamination.
  3. As the fermentation process is operated continuously, the operator should have more knowledge about fermentation, microbial behaviour and growth.
  1. Dual or Multiple fermentation process

In this fermentation process, two or more types of micro-organisms are used.. In some fermentation process some micro organism are unable to form desired product so here multiple micro-organisms are used.

In dual fermentation, first one type micro-organism is inoculated and this micro-organism makes the fermentation media suitable for growth of second type micro-organism. It reduces the oxidation reduction potential for anaerobic fermentation of second micro-organism, which in turn produces the desired product. The second micro-organism  also removes toxic products produced by the first micro-organism.

Inoculation of micro-organism in fermentation media can be done in different ways.

  1. First micro-organism is inoculated in media and allowed to grow and then second micro-organism is inoculated in media for product formation.
  2. Sometimes both micro-organisms are inoculated simultaneously in fermentation media and fermentation is carried out.

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