Beer | Bread | Chocolate | Natto | Wine | Yoghurt
Microbes are used to help preserve foods. Many microbes preserve foods by a process called "fermentation." Fermentation is the conversion of sugars to simpler compounds by microbes under conditions with no oxygen. Microbes gain energy in this process, just as we gain energy by respiration.
Grains, such as barley, are converted to beer with the help of
yeast. Hops, (flowers of hops vine), are added for flavoring and to
prevent the growth of unwanted microbes that would otherwise ruin the
Saccharomyces cereviceae, or yeast, is a fungus. When grown without air, yeast produces alcohol (ethanol).
Bread is made from grains fermented with yeast. The yeast produce the gas carbon dioxide (CO2) and the alcohol ethanol (CH3-CH2-OH). The carbon dioxide gas makes the bread rise. The ethanol evaporates during baking.
The same organism used to make beer can also be used to make bread. Kneading bread gives oxygen to the yeast so it can produce carbon dioxide so bread will rise.
Chocolate is prepared with the help of microbes. Chocolate comes from the seeds of cacao trees. These seeds are in a white fleshy pod. To get the seeds out of the pod, the pod is allowed to ferment with naturally occurring microbes that include yeasts and bacteria such as Lactobacilli and Acetobacter.
This bacterium produces an acid that helps to eat away the seed pod of chjocolate beans.
A favorite food of some Japanese, naato is served with rice. This mucous-like mush that smells like ammonia is made by the action of microbes on soybeans that have been soaked in water. The bacterium used for this fermention is Bacillus subtilis (also known as B. subtilis natto).
This is the resting stage of a bacterium like that used to make Natto.
Fruit juice is converted to wine with the help of yeast.
The same microbe used to make wine can also be used to make bread.
Yoghurt is made from fermented milk. Milk is rich in sugars, particularly the sugar lactose. Since microbes like sugars, milk is a great feast for microbes. Lactobacilli are the bacteria that convert milk to yoghurt. In the process of using the milk sugar, Lactobacillus produces acid which makes the yoghurt sour and a less hospitable place for other microbes.
This bacterium can digest lactose. It produces an acid which gives yoghurt a slightly sour taste.
© 1999 Comm Tech Lab, Michigan State University. This work was created with support from the National Science Foundation and the Center for Microbial Ecology at Michigan State University.