The Effect of Yeast on Different Fruit Juices
Picture of student researcher

Researched by Kristyn S.
2001-02




PURPOSE

The purpose of this experiment was to determine the amount of fermentation of four different fruit juices after adding yeast. 

I became interested in this idea when I saw the fruit in my familyís refrigerator starting to ferment.

The information gained from this experiment may be used by wineries to determine which fruit juice ferments best.

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HYPOTHESIS

My hypothesis is that the fruit juice with a higher percentage of sugar will produce more fermentation. 

I base my hypothesis on the World Book Encyclopedia, which states, 
"Yeast breaks down sugar obtained from fruit juice into ethyl alcohol and carbon dioxide gas for use in wine."

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EXPERIMENT DESIGN

The constants in this study were:

  • The temperature.
  • The amount of juice (250ml).
  • The amount of yeast (1g)
  • Size and shape of container
  • Time allowed to ferment.
  • Method of measurement.


The manipulated variable was the type of fruit juice.

The responding variable was the amount of fermentation as shown by the reduction of sugar.

To measure the responding variable I used a brix meter to find the percentage of sugar before and after fermentation for each sample to calculate the difference.

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MATERIALS
 
QUANTITY ITEM DESCRIPTION
1 Brix meter
16 Transparent containers 
12g Yeast 
25000ml Orange juice
1250ml Apple juice
1250ml Cranberry-grape juice
1 Cylinder
1 Gram scale
1 Thermometer

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PROCEDURES

1. Gather materials.
2. Label four containers OJ control 1,2,3 and 4.
3. Label four containers as oj1, oj2, oj3, and oj4.
4. Label four containers as ap1, ap2, ap3, and ap4.
5. Label four containers as cgr1, cgr2, cgr3, and cgr4.
6. Add 250ml of orange juice to each of the containers labeled OJ control 1,2,3 and 4.
7. Add 250ml of orange juice to each of the containers labeled OJ 1,2,3 and 4.
8. Add 250ml of apple juice to each of the containers labeled AP 1,2,3 and 4.
9. Add 250ml of cranberry-grape juice to each of the containers labeled cgr 1,2,3 and4.
10. Measure the sugar in each of the juices before adding the yeast, record results.
11. Add one gram of yeast to each of the containers labeled OJ 1,2,3, and 4.
12. Add one gram of yeast to each of the containers labeled AP 1,2,3, and4.
13. Add one gram of yeast to each of the containers labeled cgr 1,2,3, and4.
14. Allow the juice to ferment for 72 hours.
15. Use the brix meter to measure the sugar after the fermentation process, record results.
16. Subtract first measurement from the second measurement, record results
17. Compare which fruit juice produced the most fermentation, record results.

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Results

The original purpose of this experiment was to determine the amount of fermentation of 3 different fruit juices after adding a certain amount of yeast.

The results of this experiment were that the orange juice produced the most fermentation. Also the orange juice turned foamy on the surface. On the bottom of each container for each sample a "gooey" substance formed. The apple and cranberry-grape juice turned murky from the yeast and after a while bubbles formed on the surface.

See data and graphs.




Conclusion

My hypothesis was that fruit juices with a higher percentage of sugar would produce more fermentation.

The results indicate that this hypothesis should be accepted, because the orange juice, which had the highest sugar content, produced the most fermentation.

Because of the results of this experiment, I wonder if using more yeast wold produce more fermentation or if using another type of juice with two of them mixed together like the cranberry-grape juice, would produce less fermentation.

My findings should be useful to wineries because I found that the juices I used produced a large amount of fermentation therefore might make good wine.

If I were to conduct this project again I would do more trials, do a replication of the entire experiment, use more varieties of juices and use a better method of measurement .

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Research Report

Introduction

 Fermentation has been around for a very long time. People have used it for making bread, beer, wine and other products. There have been scientists and chemists who have discovered new things about fermentation. There are many types of fermentation including fermentation of fruit juices, malted grain and other sugars. 

Fermentation

Fermentation is a chemical process that breaks down organic matter. Microbes like bacteria carry out this process. Mold and yeast act upon molasses and mineral salts to create penicillin. Yeast breaks down sugar taken from malted grain and turns it into ethyl alcohol and carbon dioxide gas to make beer. French Scientist Louis Pasteur discovered that microbes ferment beer and wine. Sugar from grape juice breaks down the same way to make wine. Fermentation is also used to make bread, cheese and yogurt. Sometimes fermentation can be unhealthy; for example milk that has been fermented turns sour. There are 1900 other types of fermentation found. Fermentation is also used to make certain drugs, vitamins and some chemicals.

 In 1810 French chemist Joseph Louis GayLussac showed that alcoholic fermentation is expressed by this equation: 
C6H12O6=2CO2 + 2C2H5OH. In 1837 it was independently suggested by German physiologist Theodore Schwann, Botanist Friedrich Kutzing and French physicist Charles Cagniard de la tour that alcoholic fermentation requires yeast cells and it is a physiological function of these organisms. 

Fungi

Fungi are organisms that lack chlorophyll, the green matter that plants use to make their food. Fungi cannot make their own food, instead they absorb it from around them. According to mycologists there are over 100,000 species of fungi. Yeasts and other one-celled fungi are too small to be seen without a microscope. Most types can be seen with the unaided eye. Some of the most common fungi are mildews, molds, mushrooms and plant rusts. Fungi break down complex animal and plant materials into simple compounds. This process of decomposition enriches the soil and makes essential substances available to pants in a form they can use. Through decomposition, fungi also return carbon dioxide to the atmosphere, where green plants reuse it to make food.

Yeast

Yeast is a single celled organism. Yeast is a fungus that exists almost everywhere in nature, including the air. Bakers use yeast to make bread rise. Yeast is used for making beer, wine, and other alcoholic beverages. It consists of masses of microscopic organisms. There are 600 species of yeast, but only a few are used commercially. Yeast grows fast, and it grows best in sugar. Yeast cells reproduce by fission and budding. Bud swelling forms on a yeast cell wall, and then it breaks off to form a new single cell. 

 In the early times yeast was used for bread, beer, wine and other products. In the 1600ís Dutch Scientist Anton Van Leeuwenhoek discovered yeast cells. In 1860 French Scientist Louis Pasteur confirmed that live yeast organisms cause fermentation of beer and wine.

How Yeast Is Used

Since yeast fungi lack chlorophyll, yeast rely on other plants to supply their food. They eat sugar from sources like fruit, grain, nectar and molasses. Yeast cells produce a chemical called enzymes and ferments that break down their food. Some yeast break down sugar into alcohol and carbon dioxide gas, this process is called fermentation. Bakers yeast is used as a leavening, a substance that makes bread rise. Sugar is needed for fermentation. Bakers may add sugar to the dough to hasten fermentation. Yeast breaks down sugar into alcohol and carbon dioxide gas. A substance in the dough called gluten traps the bubbles from the gas. As the gas bubbles expand, the gluten stretches causing the bread to rise. The alcohol produced by fermentation evaporates when the bread is baking. When being baked, the bread yeast is destroyed. 

Yeast used in wine acts on the sugar in grapes and other fruits to produce alcohol and carbon dioxide gas through fermentation. Most wines allow the gas to escape into the air.  In some champagnes and sparkly wines the gas remains to provide the drinkís natural bubbles. 

Brewers yeast cannot act directly on the grain used for beer, so brewers convert the starch in the grain into sugar by means of a process called malting. Yeast is then added to convert the sugar into alcohol. The gas formed during fermentation is pumped off the beer and then added again to carbonate it. 

Yeast is also used for the production of a dietary supplement called single cell protein. Yeast produces large amounts of particular vitamins and is used in the commercial production of vitamins. Yeast used in brewing can absorb and store vitamins from their food. People eat these yeasts as vitamin supplements. Certain yeast fungus can produce large amounts of useful substances such as fat, glycerol, industrial alcohol and various enzymes. The yeast is used in the commercial production of these substances.

How Yeast Is Made

Before the commercial production of yeast in the 1890ís, yeast fungi from the air leavened the bread that people baked. Homemakers prepared dough and left it uncovered and yeasts landed on it and began the fermentation process. Later excess yeast from the beer and winemaking industries was used in breadmaking. This yeast is called barm. When bakers yeast first became an industry, manufacturers grew yeast fungi on malted grain. Today bakers yeast is produced on molasses, which consists mostly of sugar. Bakers yeast is manufactured in two forms, dried grains and moist cakes. Cakes of yeast are made up of live, active cells. Yeast cells in dried grains are live but not active. Dried yeast must be mixed with warm water before yeast fungi can grow. Yeast cakes must be refrigerated, but they spoil after about six weeks. Dried yeast doesnít need to be refrigerated but it will last longer.

 Fruit

Fruit is the part of a flowering plant that contains the plant's seeds. In this sense, fruits include acorns, cucumbers, tomatoes and wheat grains. Horticulturists define fruit as an edible, seed-bearing structure that (1) consists of fleshy tissue and (2) is produced by a perennial. Therefore horticulturists would classify cucumbers, tomatoes and rhubarb as vegetables. Yet a botanist would classify them as fruits. 

The word "fruit" refers to juicy, sweet or tart kinds of food that people enjoy as snacks or desserts. The word also comes from the Latin word "frui", meaning to enjoy. Popular fruits are apples, bananas, grapes, oranges, pears and strawberries. Many fruits are nutritious and appetizing. For example: oranges and strawberries contain large amounts of vitamin C. Most fruits have high sugar content, so they provide quick energy. Fruits cannot supply a well balanced diet because they do not supply enough protein. 

Types of Fruit

Temperate fruits must have annually cold seasons to grow properly. They must be raised chiefly in temperate zones, regions between tropic and polar areas. Most temperate fruits grow in Europe and North America, but some grow in Asia and Australia, which have major producing areas. Principal temperate fruits include apples, apricots, cherries, peaches, pears and plums.

Subtropical fruits can grow in warm or mild temperatures, but can only survive a light occasional frost. Most widely grown subtropical fruits are the citrus group, which include grapefruit, lemons, limes and oranges. Other subtropical fruits are dates, figs, olives and avocados. 

Tropical fruits are raised mainly in the tropic areas and canít survive even a light frost. Bananas and pineapples are the best known tropical fruits grown throughout the tropics and much of each crop is exported. Other tropical fruits are acerolas, cherimoyas, litchis, mangoes, mangosteens and papayas.

Sugar

Green plants produce sugar, but most table sugar comes from sugar cane or beets. Other sources of sugar are cornstarch, milk, maple syrup and honey. Sugar belongs to the class of foods called carbohydrates. Carbohydrates provide energy for plants and animals. There are two kinds of sugar monosaccharides and disaccharides. Monosaccharides are the simplest carbohydrates, include glucose and fructose. Glucose is the most important carbohydrate in the blood. Fructose is found in fruits and vegetables. Common disaccharides include lactose and maltose. Lactose is found in milk and is used in the production of some medications. Maltose is formed from starch and it is used in the production of bread and baby food.

Summary

 There are many different things needed for fermentation including, yeast, fruit juice or malted grain, and sugar. Fermentation produces many products like bread, cheese, yogurt, wine and beer. One unhealthy product of fermentation is fermented milk.

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BIBLIOGRAPHY

Ammariti, Joe F. "Fungi." World Book Encyclopedia. 1998.

Ashe, Arthur J. III. "Fermentation." World Book Encyclopedia .1999.

Ashe, Arthur J. III. "Yeast." World Book Encyclopedia. 1998.

"Fermentation." 11-14-01 http://pasture.ecn.purdue.edu/~agen5561bread/html/fermentation.html

Jules, Janick. "Fruit." World Book Encyclopedia, 1998

Moore, Paul H. "Sugar." World Book Encyclopedia.1998.

"Sugar." The New Book of Popular Science. Grolier, Inc.: Danbury, CT. Volume. 1979.

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ACKNOWLEDGEMENTS

I would like to thank the following people. Without their help, my project would not have been possible.
* My dad for transporting me to Tree Top to pick up a tool I needed for my experiment, buying me the supplies I needed for my experiment and picking me up after school from SOAR.
* John Baranowski of Tree Top for lending me that  tool and explaining how to use it.
* My sister Kaity for taking pictures of my experiment.
* My mom for helping me to make things better.
* Mrs. Helms for helping me with my display and showing me how to do things.
* Mr. Newkirk for always helping me with everything that has to do with my science project.
 
 
 


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