The Effect of Temperature on the Growth of Yeast

Researched by Samantha H.
2003-04



PURPOSE

The purpose of this experiment was to determine the effect of temperature on yeast growth.

I became interested in this idea this year when micro life like bacteria, mold, and yeast became interesting to me. I thought I should do a project on yeast since I liked the topic so much.

The information gained from this experiment could help bread bakers all over the world, by keeping the temperature to an optimal temperature so the dough can rise properly.  



 

HYPOTHESIS

My hypothesis was that at room temperature (about 20 degrees C) the bread would raise most. If the temperature were above the optimal range it wouldn’t rise as well. If it is below that range then it will also not rise as well.  

I based my hypothesis on a Seattle Times article written by Nichole Mindt. It discussed the effect of temperature on the rising of bread, “If the liquid is too cold, it will not activate the yeast and dough will require a longer rising time. If the liquid is too hot, it will kill the yeast and the dough will not rise. ” So I thought if you keep the temperature at room temperature the bread would rise properly.

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EXPERIMENT DESIGN
 

  • The constants in this study were:
  • Testing procedure
  • Type of bread
  • Size of bread
  • Place bread is stored while yeast is growing
  • Amount of light bread is exposed to
  • Amount of humidity in each group
  • Temperature for each group
  • Storage bags


The manipulated variable was temperature.  

The responding variable was how much the bread dough had risen.

To measure the responding variable I used a set of calipers to determine the diameter of the dough balls in centimeters.

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MATERIALS

QUANTITY  ITEM DESCRIPTION

 1 

 Bread Recipe

 4 
Sheets of wax paper
1 Caliper
1 cup 
Milk
1/4 cup  Water
4 tsp  Butter
3 cups Bread Flour
4 tsp Sugar
3/4 tsp Salt
1 Packet of Dry Active Yeast
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PROCEDURES

1. Lay out all of the materials.
2. Find a bread recipe.
3. Get the ingredients.
  A) Get 1 cup milk.
  B) Now get 1/4 cup of water.
  C) Get out 4 teaspoons of butter.
  D) Take out 3 cups of bread flour.
  E) Get 4 teaspoons of sugar.
  F) Get out 3/4 teaspoons of salt.
  G) The last thing needed is a packet of active dry yeast.
4. Mix all the ingredients up.
A) Put all ingredients in a bowl
B) Stir all of the ingredients.
5. Put the ingredients in a bread machine.
6. Let the bread machine knead the dough for 1/2 hour.
7. Set out 4 sheets of wax paper, 1 for each group.
8. Take the dough out of the bread machine.
9. Make dough into 3 cm dough balls.
10. Place 10 dough balls on each sheet of wax paper.
11. Let them sit for 4 hours in the controlled temperature groups: 2 degrees C, 12 degrees C, 21 degrees C, 35 degrees C.
  A) After 2 hours check on dough balls.
  B) After 2 more hours take dough balls out.
12. Measure the diameter of the dough balls in each group with calipers.
13. Record results on a data sheet.

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RESULTS

The original purpose of this experiment was to determine the effect of temperature on yeast growth.

The results of the experiment were that at 21 degrees Celsius the dough raised the most (to 5. 7cm) after four hours. 35 degrees Celsius was also one of the most (to 5. 6) temperature after four hours was 35 degrees. 12 degrees was a little lower (to 4. 6). The temperature that was the least was 2 degrees (to 3. 6). 21 degrees equals about room temperature. So the bread raised the most in room temperature.

See my data table and graph.

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CONCLUSION

My hypothesis was that at room temperature (about 20 Degrees C) the bread would raise most. If the temperature were above the optimal range it wouldn’t rise as well. If it is below that range then it will also not rise as well.  

The results indicate that this hypothesis should be accepted, because the dough that sat in the optimal range raised the best. If the temperature was too hot or too cold the dough did not rise as well.

Because of the results of this experiment, I wonder if I let the dough sit longer, would the dough rise more. I wonder if I used different bread recipes, would it change the results. I also wonder if I used different types of flour or yeast would it make a difference.  

If I were to conduct this project again I would have made more dough balls in each group. I would measure the dough balls to a more exact size initially. I would also have more temperature groups and make sure I knew the temperatures were very exact. I would repeat the entire experiment a second or third time.

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RESEARCH REPORT

Introduction

Yeast is widely used for making bread, beer, and wine. People all over the world drink and eat those products. Bread is the main product that people eat out of the three.  

Heat

Humans need heat to survive. Without heat from the sun we would not survive. We also need heat for food. If the temperature never changed and it was always hot or cold we could not grow crops. Most people don’t live in the Sahara desert or in Antarctica; this is because our bodies need a steady body temperature. Without a steady body temperature humans could not live. Anything else that is living also needs a certain temperature to live. Humans can hunt meat, but without cooking the food it does not taste as good, or is as safe. You also need cooking for killing germs. Some water can be very infected with all sorts of germs but if you boil it then the germs will get killed. Humans also need heat for manufacturing. Almost everything that humans manufacture uses heat during the manufacturing process.  

Temperature

Temperature is the relative hotness or coldness of a body or an environment.   It is also
a numerical measure of hotness or coldness on a standard scale such as Celsius and Fahrenheit.

Thermometer

A thermometer is an instrument that measures, and indicates temperature, especially one that consists of a glass tube in which a liquid expands or contracts as the temperature increases or decreases. Humans need thermometers to measure temperature. If we did not have thermometers to measure temperature we could burn or freeze our selves.

Thermodynamics

Thermodynamics are the part of physics that deals with the relationships between heat and other forms of energy. In thermodynamics there are two laws. The first law states that energy cannot be created or destroyed. The second law says that heat or energy only moves from something of higher heat energy to something of less heat.

Yeast

Yeast is any of various one-celled fungi that can cause the fermentation of carbohydrates, 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. Yeasts that are used commercially consist of masses of microscopic yeast organism. There are about 600 different types of yeast. Few of the types are used commercially. Yeast is a type of fungi that is almost everywhere.   It is even in the air. The reproduction of yeast happens very quickly.  

Substances that contain sugar are the substances that yeast grows well on. By splitting in two or budding the yeast reproduces. Part of the cell wall of the yeast swells then forms a new growth or a bud. The bud turns into its own independent cell.  

The Importance If Yeast

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 peoples’ diets worldwide.  
 

How Yeast Is Used

Yeast has a lack of 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 breaks 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.  

The History of Yeast

In the early years people didn’t know much about yeast. In the 1600’s Anton Van Leeuwenhoek, a Dutch scientist, discovered yeast cells first. In 1860 Louis Pasteur, a French scientist, confirmed the cause of fermentation of wine and beer.

Bread

People all over the world eat bread. Bread gives people energy and protein. The staff of life is what bread is often called. To make bread you have to bake dough that consists of flour or grain meal. The flour or grain meal is mixed with water or milk. The people in many Western countries mainly bake loaves or rolls made with wheat flour. People eat crispy and thin sheets of bread called flat bread in other parts of the world. Flat bread is made from grains like barley, corn, oats, rice, rye, wheat, or four made from these grains. Flat bread does not have yeast or other leavening agents to make it rise. Some people make bread by hand. In commercial bakeries bread is made by machine.

Kinds of Bread

There are mainly three groups of bread. There is yeast bread, quick bread, and flat bread. Yeast raises yeast bread. Quick bread has a quicker preparation before baking. Quick bread rises by baking powder or other substances that raise dough. Flat bread also takes less time to prepare before baking. Flat bread uses little or no substance at all to help it rise.  

There are other types of breads in the three groups. Yeast bread includes pan bread, hearth bread, and other breads that are yeast-leavened.   Pan bread is baked in a container. Pan bread includes bread made with white wheat flour and breads like raisin bread and whole-wheat bread.  

Corn bread, doughnuts, muffins, and pancakes are all included in quick bread. Most quick bread is made at home. Quick bread is also made in local bakeries and supermarkets.

Flat bread is a main food throughout the world. In Central America people eat many types of flat breads made from corn or wheat flour, called tortillas. Flat bread can also be made from rice flour. In India people eat flat bread called chapatti. Chapatti is made from coarsely ground wheat. Pita bread is another type of flat bread, is made from durum wheat.

How Yeast Bread is Made

Commercial bakers and home bakers make bread from dough consisting of at least four ingredients. These ingredients are flour, water or milk, salt, and yeast. Other ingredients that might also be in the dough are eggs, shortening, sugar, or other foods. Commercial bakers use enriched dough for white bread. To enrich the dough, bakers use vitamins and minerals. Some bakers just use already enriched flour. Dough conditioners and shelf-life improvers are in most commercial dough. For bread to be able to get a smooth and even texture bakers use chlorine dioxide and potassium bromate. Monoglycerides keep bread from getting stale and improved shelf-life. Calcium propionate reduces the growth of mold and bacteria.

 There are two processes for making dough into bread. One is conventional bread making and the other is continuous bread making. Most bakeries use the process of conventional bread making. Home bakers also use the conventional bread making process, but they vary the process. The largest bakeries use the continuous bread making process.  

When using the conventional bread making process the ingredients are mixed by one of two main methods. One is the sponge-and-dough method the other being the straight dough method. In the sponge-and-dough method the ingredients are combined in 2 stages. The first stage mixes up all of the yeast and some of the flour and water or milk. Once these ingredients are mixed this mixture is called a sponge. Bakers then let the dough rise for 16 hours at about 85° F. The other ingredients are then added to the mixture. Then it rises again for a little while. In the straight dough method all of the ingredients are put in and mixed at once. Then it rises for 3 hours at 85° F. After both of these processes the dough is cut into the right shape or size. Then they rise for a little longer. The bakers cook the dough in an oven at about 450° F.  

In continuous bread making people use highly specialized equipment. They use this equipment when they are mixing the ingredients and preparing the dough so it will be ready for baking. In the most common methods the ingredients are all added together expect the flour. This mixture is called broth. After the mixture rises in a tank the broth is pumped to a mixer and flour is added. While the ingredients are in the mixer they are put under pressure and then it forms dough. The dough is then divided and shaped. Then the dough is sent to the oven so it can be baked. The dough forms to a bread of uniform shape, texture, and quality. After the baking of the bread, it is removed from the oven so the bread can cool. When the bread is made commercially it is put in a cooling machine where there temperature drops about 100°F. Then the bread is sliced and wrapped.  
 

Summary

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.

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BIBLIOGRAPHY

Ammirati, Joe F. "Mold," World Book Encyclopedia, 1999.

Ammirati, Joe F. “Fungi,” World Book Encyclopedia, 1999.

Ashe, Arthur J. “Yeast,” World Book Encyclopedia, 1998.

Jamieson, Kay Franzen. “Bread,” World Book Encyclopedia. 1998.

Long, Alexis B. “Humidity,” World Book Encyclopedia, 1999.  

McClintock, Mike. “What the Nose Knows. ” The Washington Post. September 11, 2003: H. 02 

Midnt, Nichole. “ Do Not Be Afraid to Bake Bread. ” Seattle Post. June 1, 1988: C. 8

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ACKNOWLEDGEMENTS
 

I would like to thank the following people for helping make my project possible:

  • My parents for getting all of my materials and letting me go to before and after school classes.
  • My teachers for helping me when I had a question.
  • My sister for answering some questions that I asked her.  

 
 
 


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