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Fermentation: Basic principles, processes and gas control

Fermentation? A word that probably gets most people thinking of brewing and alcohol – perhaps even food preservation. In fact, people have been using fermentation processes for millennia to make bread, cheese, yoghurt and alcoholic drinks. Today, many industries use fermentation processes for research and production, including not only food & beverage producers but also the pharmaceutical industry.
Here you will find out more about fermentation and gas control in the fermentation process.

Where does the term ”fermentation” come from, and what does it mean?

The term “fermentation” comes from Latin and is closely related to “fermentum”, the Latin name for sourdough. Biotechnology refers to fermentation when converting organic substances using bacteria, fungi or cultures, or by adding enzymes. This produces gases, alcohol and acids. The latter enables foods to keep for longer. There are different fermentation processes, with the main difference between them being that the processes can be anaerobic (no oxygen) or aerobic (using oxygen).

Are fermentation and digestion the same?

Aren’t fermentation and digestion the same thing? These terms are frequently taken to mean the same thing. But this is not entirely true, as fermentation is just one form of digestion, while digestion is just one step in the fermentation process. Digestion is mainly used when the focus is on the breakdown of a substance with little interest in the by-products, for example in sewage digestion. We speak of fermentation, on the other hand, when the aim is to harvest by-products of the digestion process such as gases and acids, for example for food preservation or beer brewing.

The six stages of fermentation

The fermentation process can be broken down into six phases. To achieve optimum results, the process should be stopped before the stationary phase begins.

  1. Fermentation begins with the inoculation of the growth medium using the desired microorganism.
  2. During the lag phase or incubation phase, the microorganisms adapt to their new environment. Cell growth at this point is still slow.
  3. Then begins the exponential growth phase in which the growth rate continuously rises.
  4. During the slow-down phase, the growth rate is reduced due to the declining nutrient concentration.
  5. This is followed by the stationary phase, where the biomass remains constant.
  6. The process is concluded with the death phase of the microorganisms.

Application areas of fermentation

  • Production of pharmaceuticals (e.g. insulin, vaccines, antibiotics)
  • Food and beverages (bread, yoghurt and alcoholic fermentation, e.g. in beer and wine)
  • Biofuels
  • Chemicals (e.g. detergents)
  • Amino acids (e.g. glutamate)
  • Biological wastewater purification

The difference between a bioreactor and a fermenter

A suitable container, referred to as a bioreactor or fermenter, is required for a controlled fermentation process. These containers help to ensure that the fermentation occurs in a controlled fashion under optimised conditions.

                                                  Bacteria, yeasts, fungi                                         Cell cultures

Grafische Darstellung Petrischale mit Bakterien, Hefen, Pilze und Petrischalte mit Zellkulturen

Where are bioreactors and fermenters used?

Bioreactors are mainly used in the production of pharmaceuticals such as drugs, antibodies and also vaccines. Fermenters on the other hand are used in foodstuff production and for the production of lactic acid or ethanol.


The bioreactor: Structure and processes

A bioreactor’s purpose is to provide as great a product yield as possible. This requires precise control of all parameters to support the fermentation process as best possible. The type and concentration of the nutrients, the temperature, oxygen content and pH value are critical. Reproducible processes are fundamental to consistently high product quality.

Gas control
Four gases are used in the fermentation process: oxygen O₂, nitrogen N₂, carbon dioxide CO₂ and air.
A variety of inputs, for nutrient solutions or for adding inoculum to the material to be fermented.
Agitator for ensuring homogenisation throughout the entire reactor space.

Batch, fed-batch and continuous fermentation: Advantages and disadvantages

Three different processes are used in bioreactors and fermenters: the batch process, fed-batch process and continuous process. Continuous operation is a useful method in large production facilities for cost-efficiency reasons. Batch fermentation is more likely to be used in research or for smaller installations. Find out more here about the advantages and disadvantages of these methods.

The batch method

The bioreactor is completely filled before the fermentation process begins and is completely emptied when the process is complete. Between those two times, nothing is added or removed. Beer brewing, for example, uses this method.


+ Flexible
+ Low investment costs
+ Short cultivation times guarantee a low infection risk    
+ Mutation effect of cells has minimal impact


- Filling, sterilising, harvesting and cleaning cause non-productive dead times
- High level of material wear & tear
- Inoculum is required for every batch
- Product quality volatile

Grafische Darstellung eines Fermenters

The fed-batch process

Substrates are added to the bioreactor during the fermentation process. This method is used where the continuous process is not cost-efficient and where the batch process – for example due to lower substrate concentration – is not productive enough.


+ Great flexibility
+ High conversion rates due to defined cultivation time
+ Optimum control conditions
+ Semi-continuous operation


- Complex process control
- High material load
- Non-productive dead times

Grafische Darstellung Fed-Batch-Verfahren

The continuous method

Substrates are continuously added to the bioreactor in a continuous fermentation process and the yield product is extracted continuously. The continuous method is used, for example, in sourdough production or sewage treatment.


+ Automated processes that are very cost-efficient
+ Consistent quality
+ Low personnel costs    
+ Low risk of infection  


- Low production flexibility
- Consistent raw material quality required
- High investment costs for automation and sterile control
- Higher mutation risk
- Higher contamination risk means risk of product loss

Grafische Darstellung kontinuierliche Verfahren

Supplying gas to the bioreactor

To precisely control the fermentation process, it is possible to supply the bioreactor with four fermenter gases as needed: oxygen (O2), nitrogen (N2), carbon dioxide (CO2) and air. These gases must be precisely controlled to achieve the desired processes.

  • Oxygen (O2) and carbon dioxide (CO2) drive the growth process
  • Pure nitrogen (N2) controls growth rate (e.g. before harvesting)
  • Air serves as an all-purpose gas when no specific gas supply is required. It contains 21% oxygen and 79% nitrogen.
Übersicht über Gase in der Fermentation

Precise gas control in fermentation is essential to ensure that the growth process is optimised. Read more here about how gases in your bioreactor can be controlled precisely.


Mass flow meters and controllers for fermentation

Mass flow controller (MFC) from Bürkert for reproducible fermentation processes. With the help of our MFCs, you can control gases precisely – in an automated and fully reproducible fashion. The devices are compliant with USP Class VI, FDA and can be shipped with a 3.1 certificate.

Abbildung der MFC Typen 8741 und 8745.

MFC/MFM Types 8741 and 8745

Find out more about our mass flow controllers for fermentation.


Type 8741

Mass flow controller (MFC)/mass flow meter (MFM) for gases

Type 8741
  • Nominal flow ranges from 0.010 l/min to 160 l/min
  • High accuracy and repeatability
  • Very fast response times
  • Simple device exchange due to configuration memory
  • Optional: USP Class VI, FDA, EC 1935 compliant

Type 8742

Mass flow controller (MFC)/ mass flow meter (MFM) for gases

Type 8742
  • Nominal flow ranges from 0.010 l/min to 160 l/min
  • Highest measuring accuracy and repeatability with very fast response times
  • Long-term stability of the flow calibration
  • Easy device exchange due to configuration memory
  • Optional: ATEX II Cat. 3G/D or USP Class VI, FDA, EC 1935 conformity

Type 8745

Mass flow controller (MFC)/mass flow meter (MFM) for gases

Type 8745
  • Nominal flow ranges from 20 l/min up to 2500 l/min
  • High accuracy and repeatability
  • Communication via standard signals or Industrial Ethernet
  • Electromagnetic and motor-driven valve actuation available
  • Easy device exchange through configuration memory

Type 8746

Mass flow controller (MFC)/mass flow meter (MFM) for gases

Type 8746
  • Nominal flow ranges from 20 l/min up to 2500 l/min
  • High measuring accuracy and repeatability with very fast response times
  • Long-term stability of the flow calibration
  • Simpler device exchange due to configuration memory
  • Optional: ATEX II Cat. 3G/D or USP Class VI, FDA, EC 1935 conformity