Yeast



Yeast 2879
Photo by: Fyle

Yeast are microscopic, single-celled organisms that are classified in the family Fungi. Individual yeast cells multiply rapidly by the process of budding, in which a new cell begins as a small bulge along the cell wall of a parent cell. In the presence of an abundant food source, huge populations of yeast cells gather. The cells often appear as long chains with newly formed cells still attached to their parent cells, due to the short budding time of two hours.

Yeast are among the few living organisms that do not need oxygen in order to produce energy. This oxygen-independent state is called anaerobic (pronounced a-na-ROE-bik; "without oxygen"). During such anaerobic conditions, yeast convert carbohydrates—starches and sugars—to alcohol and carbon dioxide gas. This process is known as fermentation.

The fermentation process of yeast is caused by enzymes, catalysts in chemical reactions similar to the digestive enzymes in the human body. In fact, the word enzyme means "in yeast." Certain enzymes in yeast act on starch to break down the long chainlike molecules into smaller units of sugar. Then other yeast enzymes convert one kind of sugar molecule to another. Still other enzyme reactions break apart the sugar molecule (composed of carbon, hydrogen, and oxygen atoms) into ethyl alcohol and carbon dioxide. The series of reactions provides the yeast cells with the energy necessary for their growth and division (form of reproduction).

In nature, yeast enzymes break down the complex carbon compounds of plant cell walls and animal tissues, feeding on the sugar produced in the process. In this way, yeast function as natural decomposers in the environment.

Words to Know

Anaerobic: Living or growing in an atmosphere lacking oxygen.

Budding: Process by which a small outgrowth on a simple organism grows into a complete new organism of the same species.

Enzyme: An organic compound that speeds up the rate of chemical reactions in living organisms.

Fermentation: Chemical reaction in which enzymes break down complex organic compounds into simpler ones.

The importance of yeast for humans

The by-products of fermentation—carbon dioxide and alcohol—have been used by humans for centuries in the production of breads and alcoholic beverages. Before the mid-nineteenth century, however, bakers and brewers knew very little about the nature of the organisms that helped

Yeast, or Anthrocobia muelleri. (Reproduced by permission of Phototake.)
Yeast, or Anthrocobia muelleri . (Reproduced by permission of
Phototake
.)

make their products. The experiments of French microbiologist Louis Pasteur (1822–1895) showed that fermentation could only take place in the presence of living yeast cells. He also deduced that anaerobic conditions were necessary for proper fermentation of wine and beer (in the presence of oxygen, yeast convert alcohol to acetic acid [vinegar]).

Brewer's yeast is added to liquids derived from grains and fruits to brew beer and wine. The natural starches and sugars in the liquids provide food for the yeast. Deprived of oxygen during the fermentation process, yeast produce alcohol as a by-product of incomplete sugar breakdown. Yeast that occur naturally on the skins of grapes also play a vital role in fermentation, converting the sugars of grapes into alcohol for wine production.

Baker's yeast, another variety of yeast, are added to a dough made from the starchy portion of ground grains (such as wheat or rye flour). The yeast break down some of the starch and sugar present in the mixture, producing carbon dioxide. The carbon dioxide bubbles through the dough, forming many air holes and causing the bread to rise. Since oxygen is present, no alcohol is produced when the bread is rising. When the bread is baked, the air holes give the bread a lighter texture.

In recent times, yeast have been used to aid in the production of alternative energy sources that do not produce toxic chemicals as byproducts. Yeast are placed in huge vats of corn or other organic material. When fermentation takes place, the yeast convert the organic material into ethanol fuel. Present-day geneticists are working on developing yeast strains that will convert even larger organic biomasses (living material) into ethanol more efficiently.

[ See also Brewing ; Fermentation ; Fungi ]



User Contributions:

1
James
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Jun 24, 2009 @ 6:06 am
Thanks, this was very usefull and included information which similar articles didn't. Keep up the good work.
2
Dani
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Oct 22, 2009 @ 11:23 pm
Wow!! this is really going to help me with the school project I am doing!!
3
yolande
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Dec 9, 2009 @ 1:13 pm
Just the info i was looking for, very informative, thank you very much.
4
Kathleen
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Dec 18, 2009 @ 7:07 am
I have been told by my doctor that I have an high excess of ethanol in my stomach. This has caused me a lot of problems over the years especially with regard to a feeling of lightheadness on a almost continual basis. I do not drink alcohol or eat yeast products. What i would like to know is if there is any way of neutralizing this other than by going on a very strict diet of no carbohydrates and taking probiotics
5
dan
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Jan 4, 2010 @ 3:15 pm
Amazing i am doing a project on yeast right now so it helped alot. p.s. loved the picture of reproduction of cells
6
Lillian
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Jan 23, 2010 @ 2:14 pm
AWESOME ARTICLE!!! Helped me out with a lot of research for my science project.

Thanks so much!!
7
Sarah
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Mar 7, 2010 @ 10:10 am
this really helped me with school homework! very helpful on the science part, whereas it was impossible to find other websites that gave detail like this, or were even relevant to my search :)
8
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Mar 28, 2010 @ 7:07 am
this really helped me in my biology assignments thank you..amazing artcicle btw
9
James
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Jul 20, 2010 @ 12:00 am
Absolutly briliant article
Well done and thanks.
Will help majorly in Science Project!


Cheers,
James
10
T Dutta
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Feb 20, 2011 @ 11:11 am
This article is informative but fails to name the scientific names of the enzymes involved in the fermentation process and the raising of bread.
11
La
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Sep 25, 2011 @ 12:00 am
Great article, however i would also like to know what the scientific names are of the enzymes used? Because i am finding it difficult to find research on the actual names of ALL the enzymes that are involved in fermentation, as well as their specific roles in the process. Any chance of help with this?
Thanks :)
12
EWOcean
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Mar 9, 2012 @ 8:20 pm
In response to LA: I think it would be highly difficult to note down all fermentation process names/
I've found this article especially useful since I'm researching for a Yeast Respiration experiment at school. Would it be possible to put up a chart that displays the reaction of yeast?
eg.
Yeast + Sugars + Anaerobic Environment --> Ethyl Acid (ethanol, alchohol) + Carbon Dioxide + 2 ATP
Yeast + Sugars + Aerobic Environment --> Acetic Acid (vinegar) + ? (What should substitute the question marks?)
13
stephka
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Mar 14, 2012 @ 2:02 am
This is helpful. Descriptive and informative. And on a black background. I love websites that have a black background. like blackle...
anyways, cheers brahh
14
Katie
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Oct 4, 2013 @ 8:20 pm
Hello! Thank you so much for this informational article! It was a great help.
15
Cameron
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Feb 16, 2014 @ 5:17 pm
Thanks for the informational article was very useful!
16
s-gill
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Mar 27, 2015 @ 2:14 pm
thanks soo much. was tons of help for my yeast project.
17
Cara
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May 31, 2015 @ 10:10 am
This was so helpful! Right now for me it is 1:12am on the morning that my assignment is due and I had barely found any useful information until I came across this website. THIS SAVED ME! Thank you so much for putting all this information in such an easy to understand format!
18
kos-faith tumun
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Aug 10, 2015 @ 11:23 pm
THIS INFORMATION WAS VERY INTERESTING AND HELPFUL. IT WAS AN EYE-OPENING PIECE OF STATISTICS THAT WILL DEFINITELY BE VERY HELPFUL IN MY UP-COMMING ASSESMENT. I AM THANKFUL FOR THIS SATISFYINGLY FASCINATING DATA. TRUELY THIS SITE IS DEFINATELY SCIENCE CLARIFIED--- IT REALLY IS CLARIFYING... :-)
19
Sara
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Feb 3, 2016 @ 3:15 pm
This will help me very much on my school project. Thanks for a great, informative article!
20
Justin
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Apr 23, 2016 @ 2:02 am
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21
daren
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May 14, 2016 @ 2:02 am
Awesome article.. Should have included scientific names of various fungi...Keep it up!!
22
Simaran
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Jun 6, 2016 @ 12:00 am
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23
Michael
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Nov 21, 2016 @ 2:14 pm
I was confused with a science homework, this basically completed my homework but giving me information at the same time, i couldnt find any of this else where so thank you!
24
shanika ricketts
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May 1, 2017 @ 3:15 pm
for sure it is awesome and this basically complete my assignments
25
Alexis
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Aug 30, 2017 @ 3:15 pm
I love this site so much. It helped me with my science fair project!

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