Whether for better or for worse, yeast are important to humans. The fermentation of beer and the leavening of bread are among yeast's positive contributions; however, many have experienced the negative consequences of yeast in the form of vaginal yeast infections and oral thrush.
Many feel that they simply cannot live without yeast and its benefits, while others find yeast to be quite a nuisance. Very few have not heard of these microbes. Even though many can identify a yeasty-tasting beer, or understand the importance of yeast for leavening bread, they are not sure exactly what yeast are.
Yeast Is Fungus
Yeast belong to the Fungi Kingdom. Like animals, they are eukaryotes, meaning that their cells have nuclei. They are single-celled organisms.
Like all fungi, their cell membranes are made of chitin, a polysaccharide that is responsible for the hard, exoskeleton–or shell, of animals such as crabs and lobsters. According to Biology, written by Robert J. Brooker, Erip P. Widmaier, Linda E. Graham, and Peter D. Stiling, and published by McGraw-Hill in 2008, a chitin molecule consists of eight carbon atoms, 13 hydrogen atoms, five oxygen atoms, and a nitrogen atom. This tough, chitinous wall protects the yeast from bacterial attacks.
Yeast are like humans in the sense that they must find food to eat in order to make energy for cellular processes. It is this process that makes them so useful for producing various foods, such bread, beer, and wine.
Yeast Infection
Humans can acquire yeast infections either by breathing in the spores or ingesting or having some other direct contact with yeast. This is inevitable. In many cases, yeast infection occurs because there is an imbalance in body chemistry, or the environment changes to one in which yeast can thrive.
Certain types of bacteria can either promote or inhibit the growth of fungus. Many kinds of beneficial bacterial live in the human body. In normal amounts, these bacteria can prevent a yeast infection, such as a vaginal yeast infection and oral thrush, from developing.
Side effects of antibiotics often include yeast infections because the antibiotics kill the good bacteria along with the bad. This creates an environment in which yeast may thrive, leading to the characteristic itching and burning symptoms. Some yeast infections can be treated by consuming foods that are rich in beneficial bacteria, such as yogurt or kefir that is enriched with live active cultures.
Beer, Wine, and Baking Yeast
Yeast use oxygen for respiration, or aerobic respiration; however, according to the NASA News article, "Planets in a Bottle––More About Yeast," by Dr. Tony Phillips and Dr. David Noever (Science.nasa.gov Accessed April 7, 2010), "In the absence of air, they derive energy by fermenting sugars and carbohydrates to produce ethanol and carbon dioxide. When yeast are supplied with both sugar and oxygen, the colonies grow up to 20 times faster through cell division than without oxygen."
It is the carbon dioxide that causes the rising of bread and the carbonation in beer and sparkling wine. The ethanol is released during the baking process, but remains as the alcohol in beer and wine.
Yeast have been shown to withstand greatly-varying temperatures. Their spores float in the air and can land on food and in beverages. According to Phillips and Noever, this contributed to sourdough bread that "did not depend on adding starter cultures." They have been used for baking for more than 4,000 years, but their importance to bread and wine was not understood until Louis Pasteur brought them to focus in 1859.
It is important to note that there are many species of yeast. Some may lead to infection while others are tasty little buggers, or at least help produce tasty food. No matter their role, yeast have greatly impacted human lives.
Diane Ursu - Diane Ursu joined Suite101 as a contributing writer in August 2009 and became a Feature Writer in January 2010. She is a freelance writer ...
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