Microbes can be used by industry to mass produce certain important chemicals. Some of these, like insulin are used in medicine to treat patients.Microbes are very efficient and produce less waste than chemical means. Often a product cannot be made any other way. Below is a diagram of a typical fermenter.
The vessel itself is made from stainless steel which does not corrode or affect the microbes and fermentation products. It can also be easily cleaned. Microbes and nutrients are put into the fermenter and air is bubbled through so that the microbes can respire aerobically. As carbon dioxide builds up the gas outlet releases it to avoid build up of pressure. A water jacket surrounding the fermenter maintains an optimum temperature so the proteins do not become denatured. Temperature, pH and oxygen probes are linked to a computer which monitors the conditions inside the vessel. Paddle stirrers ensure that the microbes, nutrients and oxygen are well mixed and distributes the heat evenly. The product is run off from the bottom. It is separated from the microbes and purified so that it can be sold or distributed.
There are a number of different chemicals which can be made using microbes in fermeters.
Vinegar is made by converting ethanol into ethanoic (ascetic) acid using microbes. Ethanol, microbes and oxygen are mixed in a fermenter. Wood shavings are added to increas the surface for the fermentation by themicrobes.
Alcohol can be made from cane sugar waste and yeast. The resulting ethanol is often mixed with petrol to create Gasohol, a cheap fuel for cars.
A simplified version of the fermenter can be used to create natural gas for use as a fuel. Household or farm waste is put in the fermenter. Anaerobic bacteria produce methane as the waste is broken down.
Chemicals like insulin and penicillin are often made in large fermenters for use in medicine.
Industrial fermenters usually have:
• an air supply - to provide oxygen for respiration of the microorganisms
• a stirrer to keep the microorganisms in suspension and maintain an even temperatue
• a water-cooled jacket to remove heat produced by the respiring microorganisms
• instruments to monitor factors such as pH and tempereature - these are tehn adjusted to ensureconditions remain optimum for the enzymes in the organism being grown
• everything needs to be sterile (air, fermenter, nutrients) to ensure that there are no unwanted microbes that may:
- make toxic waste products
- be pathogenic
- compete with the cultured microbes for food or oxygen
Mycoprotein is made in 40 metre high fermenters which run continuously for five weeks at a time.
The fermenter is sterilised and filled with a water and glucose solution. Then a batch of fusarium venenatum, the fungi at the heart of Mycoprotein, is introduced.
Once the organism has started to grow a continuous feed of nutrients, including potassium, magnesium and phosphate as well as trace elements, are added to the solution. The pH balance, temperature, nutrient concentration and oxygen are all constantly adjusted in order to achieve the optimum growth rate.
The organism and nutrients combine to form Mycoprotein solids and these are removed continuously from the fermenter after an average residence time of five to six hours. Once removed the Mycoprotein is heated to 65°C to breakdown the nucleic acid. Water is then removed in centrifuges, leaving the Mycoprotein looking rather like pastry dough.
The Mycoprotein is then mixed with a little free range egg and seasoning to help bind the mix. It is then steam cooked for about 30 minutes and then chilled, before being chopped into pieces or mince.
The product is then frozen. This is a crucial step in the process because the ice crystals help to push the fibres together, creating bundles that give Mycoprotein its meat-like texture.
The pieces and mince are then sold under the Quorn™ brand and also in wide array of products ranging from escalopes to ready meals, deli slices to sausages.