Copyright © 2007 Dorling Kindersley
The use of microbes (micro-organisms) to produce and process materials is called biotechnology. Bacteria and yeasts are used to produce products, such as yogurt, cheese, and wine, by FERMENTATION.
Microbes are like tiny chemical factories. They make chemicals called enzymes (biological catalysts) to break down chemicals in their surroundings for food. As microbes feed and multiply, they produce chemical by-products. Yeast cells make an enzyme that turns sugar into alcohol.
Some microbes produce chemicals that kill disease-spreading bacteria. These chemicals are antibiotics. They either destroy the bacteria completely, or stop it from multiplying. The first antibiotic, penicillin, was made from a mold that grows on bread. Its antibiotic action was discovered by chance in 1928.
Fleming won the Nobel Prize for Medicine in 1945 for the discovery of penicillin. While searching for compounds that would kill bacteria without harming the body, he noticed that bacteria cultured (grown) in a glass dish had died around spots of mold. The mold had blown in through a window. Fleming extracted the antibiotic substance from the mold and called it penicillin.
Fermentation is the action of yeasts and bacteria on the sugars in fruit, grains, milk, and other food. Yeast cells added to bread dough feed on its natural sugars, turning them into carbon dioxide and water. This makes the dough rise to make light, fluffy bread.
An enzyme called rennin is added to milk. It ferments the milk sugars to produce lactic acid. The acid separates the milk into solid curds and liquid whey. The curds are pressed into cheeses. Microbes continue to work in the cheese as it ages, making its flavor stronger and changing its texture.
Natural yeast on grape skins ferments the fruit sugars to produce alcohol. Fermentation stops after 10 to 30 days, when all the sugars have been used up, or when the alcohol content is 12 to 15 percent, which stops yeast cells from working. The wine is sealed in barrels. If it is exposed to the air, the alcohol is oxidized to acetic acid (vinegar), and the wine turns sour.