Dedication – – – – – – – – i
Acknowledgment – – – – – – – ii
Table of contents – – – – – – – iii
Overview – – – – – – – – – iv
Introduction – – – – – – – – 1
Yeast. – – – – – – – – – 2
Types of yeast – – – – – – – – 2
Importance of yeast – – – – – – 3
How yeast is used – – – – – – – 3
Temperature – – – – – – – – 4
How does temperature affect yeast? – – – 5
Medicinal value of yeast on human health. – – 8
Conclusion and summary – – – – – 10
Reference – – – – – – – – – 11


Yeast cells respire aerobically if there is enough oxygen supply. If there is not enough oxygen present then fermentation will take place as the yeast cells have to respire anaerobically. Fermentation makes energy that is used for cell growth. When yeast cells ferment they also produce ethanol (alcohol) which is important to brewers. The yeast cells need sugar to ferment as without sugar, the yeast cells would not be able to respire at all. The sugar supply provided is called sucrose, Enzymes in the yeast cells break down the sucrose into glucose. Yeast reproduces by budding in other words when the yeast cell grows too big. It splits to make two metical copies of itself. This form of reproduction is called asexual as it only involves one parent cell. Yeast needs amino acids to build into proteins so it cans growth. Anion acids are supplied by malt extract.



The word “Yeast” comes to us from the old English gist, gyst and from the indo-European root yes-meaning boil, from or bubble.

Yeast microbes are probably one of the earliest domesticated organizing. People have used yeast for fermentation and baking throughout history.

Archaeologists digging in Egyptian ruins found early grinding stones and baking chambers for yeasted bread, as well as drawings of 4,000. years- old bakeries and breweries. (Phillips 2012) in 1680, the Dutch naturalist Anton van leeuwenhock first microscopically observed yeast but at the time he did not consider them to be living organisms but rather globular structures (Huxley, 1871) in 1857 French microbiologist louis Pastear. Proved in the paper “memire sur la fermentation alcoolique” that alcoholic fermentation was conducted by living yeasts and not by a chemical catalyst. (Barntt 2003). Pasteur showed that by bubbling oxygen into the yeast broth, cell growth could be increased but fermentation was inherited as an observation cater called the “Pasteur effect”


Yeast is any of various one called fungi that can cause the fermentation of carbondydrates producing carbon dioxide and alcohol. Bakers put it in bread to make it rise. Yeast is also used for the production of beer and wine. Yeast that are used commercially consist of masses of microscopic yeast organism.


Yeats is a very interesting little organism. It is neither a plant nor an animal but a single called fungus. As such there are several different species and varieties of yeast. And just like the apples you choose to make year cider, each one will make the end product taste a bit different. The difference in come is because of the rate of sugar consumption and carbon dioxide and other waste product creation as well as temperature and PH needed for fermentation.

The two main types of yeast are baker’s and brewer’s yeast. White both are saccharomyces cererisiae, they are different strains (Like the difference between red delicious and Macintosh applies). The active dry yeast that you can get in grocery store is bakers yeast and is used for baking bread. To brew hard cider you want brewers yeast. This comes in dry and liquid forms.


Yeast is important because it is used for making food which people eat.

Yeast is used in the making of bread beer and wine. Bread in particular is an extremely important part of people diets world wide.


Yeast lack chlorophyll. The lack of chlorophyll in yeast means that yeast has to rely on other things for food. Fruit grain, nectar and molasses are the things yeast feeds on for sugar. Yeast break down its food by producing a chemical called ferments or enzymes. Some species of yeast break down their food into alcohol and carbon dioxide. That process is called fermentation. Fermentation is important in making bread, beer and wine.

Temperature: Temperature is the measurement in degrees of how hot or cold a thing or place is (Oxford dictionary 6th edition 2000).



Yeast is any various one called fungi that can cause the fermentation of carbohydrates producing carbon dioxide and alcohol.

At low temperature (0-10oc) yeast will not grow but die either. At temperature (100c-35c) yeast will grow and multiply faster at higher temperature with an optimal growth at (30 or 37oc) (that depends on the species). At higher temperature the cells becomes stressed meaning that their content becomes damaged and which can be repaired to some degree.

A high temperature (>50oc) the cells die. The Bacteria can survive freezing under certain conditions.

(Wassenaar 1989) when baking bread all yeast dies during the process.

Most microbes such as bacteria and yeast have an optimal temperature range in which they grow best.

If it gets either too low or too high then they grow much slower and finally cease growing.

However, this temperature range can vary with different organisms.

For example, yeast grows optimally around 300c – 350c. if it rises above 400c it won’t grow at all. Below 300c, it slows down dramatically and when it gets below 10oc if really doesn’t grow much at all, so what causes this?

The main reason is the ability of the enymes that catalyze all biochemical reactions in the yeast cell to function at those temperatures.

Enzymes have an optimal temperature range. When they get below that range their ability to catalyze the intended reaction slows down. Above that temperature, the enzyme begins to denature or unfold and becomes inactive. Each enzymes will have a different range where it becomes inactive (Ammirati 1999).

For an organism to stop growing at some temperature, you don’t need all the enzymes to become in active you just need one essential enzyme to stop working and then the organism fails to grow. So which ever is the first essential enzyme to get inactivated defines the maximal temperature at which that organism can grow (Ammirati, 1999).

(Alexis, 1999), some bacteria for example have becomes adapted to grow at unusual temperatures. There are thermophilic bacteria that grow in hot spring and similar places and grow fine at very hot temperatures. Some at 60 – 70 degree Celsius. A few grow above 800c or even 900c. The enzymes in this microbes have changed so that they can tolerated the high temperature.

A microbe that grows optimally at 650c may completely unable to grow at 370c.

Likewise there are some bacteria which are cold adapted and grow at very low temperatures but would be unable to grow at room temperature.



Yeast is the product of rice fermented with monaseus purpureus yeast. Yeast supplements are different from red yeast rice sold in chiness grocery stores. People use yeast as medicine. Yeast is used for maintaining desirable cholesterol levels in healthy people, reducing cholesterol on people with high cholesterol, for indigestion, diarrhea, improving blood circulation and for spleen and stomach health.

In foods yeast is used as a food colouring for peking duck. The active ingredient in yeast is the same as the active ingredient in prescription drugs called statin used for high cholesterol. That’s why yeast has all the possible side effects, drug interactions, and precautions associated with this type of drug. The American heart Association (TAHA) warns against using yeast until results of long-term studies are in. you should tell your health care provider if you plan to take yeast (Huang, 2006).

You may have come across a yeast product called cholestin manufactured by pharmenex. It was one of the most widely studied yeast products originally, cholestin contained the same active ingredient found in statin drugs. This caused the food and drug Administration (FDA) to call cholestin an unapproved drug. Cholestin was reformulated so that this ingredient is now something else.



Yeast is useful and important to humans in many ways. Temperature is very important to yeast growth. Yeast is used in bread, which is imperative because most people eat bread. We could live without bread but it is still important worldwide.


Ammirati Joe F. (1999) fungi” blood book Encyclopedia.

Alexis long .B. (1999) “Humidity” Word Book Enyclopedia.

Barnet J. (2003) beginnings of Microbiology and biochemistry: the contribution of yeast research 149 (3): 557-567.

Huxley A. (1871) “Discourses: Biological and geological” Volume 111.

Hornby A.S. (2000) Oxford Dictionary 6th edition.

Phillips T. (20012) “planets in a battle: more about yeast” www.secience.nasa.gov. Wednesday 28/6/2012 5pm

Wassenaar (1989) “bread” Word Book Encyclopedia.