Why microorganisms are used to make food

1. Biotechnology is the use of living organisms, or of processes carried out by them, to make useful products on a large scale.
2. Microorganisms are the organisms used, because a bacterium or a yeast cell can divide every twenty minutes or so, which means a culture doubles many times in a single day.
3. They feed on cheap and simple nutrients, including sugars and waste materials left over from other food industries, so the raw materials cost little.
4. They are grown indoors in tanks, so production does not depend on the weather, the season, the soil or the number of hours of daylight.
5. A tank occupies a very small area compared with the farmland needed to produce the same mass of protein, so the land freed up can be used for other crops or left as habitat.
6. Microorganisms are also the easiest organisms to modify genetically, because a bacterium has a single circular chromosome and plasmids that are simple to work with.
7. The product is either the cells themselves, which are harvested as food, or a substance the cells release into the liquid around them, which is separated out and purified.

Growing microorganisms in a fermenter

1. A fermenter is a large sterile vessel in which microorganisms are grown in controlled conditions so that they make a useful product.
2. Industrial fermenters are made of stainless steel, which does not react with the culture and can be cleaned and sterilised with steam between batches.
3. Everything entering the fermenter is sterilised first, because any other microorganism that got in would compete for the nutrients and could spoil or contaminate the product.
4. Nutrients are added as a controlled supply of a carbohydrate for respiration, a source of nitrogen for making amino acids, and the mineral ions the cells need.
5. A water-cooled jacket surrounds the vessel, because respiration releases heat and without cooling the temperature would rise until the enzymes in the cells denatured.
6. Keeping the temperature at the optimum for those enzymes keeps the rate of respiration and of product formation as high as possible.
7. A motorised stirrer with paddles keeps the cells suspended in the liquid rather than settling, and spreads nutrients, oxygen and heat evenly through the vessel.
8. Sterile air is bubbled in when the organism respires aerobically, so that oxygen never becomes the factor limiting growth.
9. Probes monitor temperature and pH continuously, and small volumes of acid or alkali are added automatically to hold the pH at its optimum.
10. When the batch is finished the culture is drained off, the cells or the product are separated from the liquid, and the vessel is cleaned and sterilised for the next batch.

Mycoprotein as a source of food

1. Mycoprotein is a protein-rich food made from the fungus Fusarium venenatum grown in a fermenter.
2. The fungus is supplied with glucose syrup as its carbohydrate source and ammonia as its source of nitrogen for making amino acids.
3. Oxygen is bubbled through the vessel because the fungus respires aerobically, and this releases the energy it needs to grow.
4. The fungus grows as fine threads, and it is these threads that give the harvested product a fibrous texture similar to meat.
5. The harvested biomass is heat-treated to lower the amount of RNA it contains, then dried and pressed into blocks.
6. Mycoprotein is high in protein and in fibre and low in saturated fat, and it contains no animal material, so it suits a vegetarian diet.
7. Producing a kilogram of mycoprotein uses far less land and water than producing a kilogram of beef protein, and it can be produced at the same rate all year round.

Genetically modified microorganisms in food production

1. Because a microorganism can be given a gene from another species, it can be made to produce a protein it would never normally make.
2. The modified cells are then grown in a fermenter in exactly the conditions described above, so the protein is produced continuously and in large amounts.
3. Chymosin is the clearest example, since the enzyme that clots milk in cheese making used to be taken from the stomach lining of calves.
4. The gene for chymosin was inserted into yeast and bacteria, which now make the enzyme in fermenters, so cheese can be made without slaughtering calves and is suitable for vegetarians.
5. The enzyme produced this way is also pure and identical from batch to batch, which makes the cheese more consistent than it was when the supply depended on animals.
6. Other modified microorganisms produce enzymes used to break down starch into sugar syrups, vitamins added to foods, and flavourings and colourings.
7. The same technology in the same vessels produces medicines such as human insulin, and those medical uses are covered separately.
8. The concerns raised are the same as for any genetically modified organism, which is why the products are tested and regulated before they reach the food supply.