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 The Effect of Ultraviolet Light on the Fermentation Rate of Yeast.

Researched by Michael M.














The constants in this study were: 
  -The amount of yeast 
  -The kind of yeast 
  -The UV lamp and its distance from the fermentation flask 
  -The size and shape of the fermentation flask 
  -Quantity and type of apple juice 
  -The temperature at the time of fermentation

The manipulated variable was whether or not the yeast was subjected to UV light during fermentation.

The responding variable was the amount of CO2 produced by the yeast as it fermented the apple juice.

To measure the responding variable I used a graduated cylinder and measured how much water was displaced by CO2 put out by the yeast during fermentation.










 Measuring cylinder


 water bath




clamp and stand

? teaspoon 

 UV lamp



100 ml

plastic tube


apple juice




Heating pad




Paper pad




The purpose of this experiment was to determine the effect of ultraviolet light on yeast fermentation.

I became interested in this idea when my dad was telling me about his job, installing water softeners and UV water filters.  I wondered why ultraviolet  purifiers were so popular and what made them work.

The information gained from this experiment will inform juice makers about a new way to pasteurize juices. 




My hypothesis is the UV light will effect the fermentation rate of yeast in apple juice by reducing the rate of yeast fermentation but not eliminating it.

I base my hypothesis on the fact that ultraviolet light will kill bacteria.  That is why some people install UV filters to purify their water.




1. Get all materials.

2. Fill the water bath with water.

3. Fill measuring cylinder with water.

4. Put plastic wrap over measuring cylinder.

5. Flip the water-filled measuring cylinder over in the water bath.

6. Get the plastic tubing and attach one end to the rubber stopper.

7. Put 100ml-apple juice into 250ml flask.

8. Heat apple juice in microwave for 25 seconds.

9. Put 1/4-teaspoon yeast in flask.

10. Shake flask to mix apple juice with yeast.

11. Plug in heat pad.

12. Put flask on heat pad.

13. Slide the stopper into the top of the flask.

14. Place the rubber tubing into the water bath.

15. Slip the plastic tubing up inside the cylinder.

16. Put a straw on other side of measuring cylinder to balance it.

17. Clamp cylinder to support measuring cylinder in an upright position.

18. Watch for CO2 bubbles in the measuring cylinder.

19. Record volume of captured CO2 in the measuring cylinder every 10 minutes for one hour.

20. Repeat steps 1-14 with the following exception.

21.  Place an UV lamp so it shines directly on the flask and the yeast during fermentation 



The original purpose of this experiment was to determine the effect of ultraviolet light on yeast fermentation. 
The results of the experiment were the UV light did effect the fermentation rate of the yeast.  The amount of displaced water was about 60 milliliters.  Also discovered was that on the UV light trial the water level went down about 30 ml every ten minutes.  Also on the control test it went down about 30 ml every ten minutes. If this was true and both of the test went down at about the same rate the amount of displaced water would be the same in both of the test, but in the UV test the water level didnít change for the first 20 minutes.  In the control test it had gone down 30 ml by the time 20 minutes of the experiment had passed.  Then after that it went down at a slightly slower rate.  The rate of bubbles in the UV light was much slower towards the end of the experiment than the control test.My hypothesis was the UV light will effect the fermentation rate of yeast in apple juice. 





The results indicate that this hypothesis should be accepted.  The rate of yeast fermentation was reduced by the UV light but it wasnít eliminated.

Because of the results of this experiment, I wonder if UV light was used on a large scale to pasteurize juice if it would be more or less effective then heat pasteurization.

If I were to conduct this project again I would have used a more scientific method of recording my results and would have done more trials and averaged them.  A stronger UV light would have produced interesting results. 




Yeast is a single celled organism.  It is a type of fungi, but there are hundreds of subspecies of yeast.   And UV is a form of light lower than visible ligth on the spectrum.

Ultraviolet light

Ultraviolet light is an invisible part of the light spectrum.  That means itís a form of light that human beings canít see.  Ultra violet light is measured in angstroms.  An angstrom is 1 hundred millionth of an inch.  A piece of paper is 1 million angstroms.  There are three different kinds of UV light.  The near ultraviolet light is closest to visible light on the spectrum.  It is abbreviated NUV.  It is from 1800-3000 angstroms.  Some of the satellites that explore the near UV light are the Hubble Space Telescope, Astro 1&2 and The International Ultraviolet Explorer.  On the other end of the ultraviolet spectrum is the extreme ultraviolet.  It is from 100 ­900 angstroms thick and is next to x-rays on the spectrum.  It is the most energetic of all the UV light lengths.  Some of the satellites exploring the extreme UV are the Extreme Ultraviolet Explorer and one that hasnít been launched yet is the ORFEUS-SPAS II.  The kind of UV light in the middle of near and extreme is far UV.  It is the least explored even though it was the first to be explored by a satellite called OAO-3/Copernicus.  It was a satellite launched by NASA to measure and observe the amount of UV light put out by stars.  Far UV is from 900-1800 angstroms.  Satellites currently exploring the far UV are Astro 1&2, International Ultraviolet Explorer and the ORFEUS-SPAS II.  The hotter the object is the more UV light it puts out, but the UV light put out by stars is absorbed into the Earthís atmosphere.  To measure the UV light put out by stars,  scientists have to launch satellites into orbit.  UV light is effective in destroying bacteria if it is around 300 nanometers.  It can produce Vitamin D in the human body if it is around 320nm, but over exposure causes sunburns.

Electromagnetic Spectrum and Visible Light

The electromagnetic spectrum is a spectrum of all light that we no of.  It goes from 
Billionths of an angstrom to tens of millions of angstroms.  And there is still more to explore.  Visible light makes up a very small part of the whole spectrum.  In fact it is only from 3200-7000 angstroms.  First on the spectrum are Gamma rays, then x-rays, next is UV light.  Then are visible light, infrared and radio waves, respectively.   Visible light runs through blue to green to yellow to orange to red.  Red light is the least energetic and close to infrared and radio on the spectrum.  Blue is the most energetic, close to UV light.

Yeast & Fungi

 Yeast is a single celled organism.  They are a kind of fungi.  There are over 100,000 of different kinds of fungi in the world.  Fungi live everywhere, including in the air, on the ground, in water and even in animalís bodies.  Fungi are plants but they donít have any chlorophyll, the chemical that makes plants green in color.  They canít produce their own nutrition so fungi get their nutrition by absorbing it from other organisms.  Some fungi are parasitic.  They can destroy entire crops of plants like wheat and corn.  There are scientists that study fungi called mycologists.  Fungi are high in protein and Vitamin B.  Yeast is known for mostly one thing.  It is responsible for making bread rise and producing alcohol in beer and wine.  Yeast is said to have first been noticed when an Egyptian bread maker was making bread for the king.  Bread in those times didnít have yeast so it didnít get fluffy He got lazy and fell asleep.  When he woke up the bread was fluffy and collapsible.  It was this way because it was left out and yeast landed on it. 

Pasteurization & Fermentation

Fermentation is a chemical change.  Enzymes trigger the chemical change.  It is a change from starch to complex sugars to simple sugars to alcohol.  This breakdown is called catalysis.  Catalysis can happen in human intestines, which causes pain.  The chemical change consists of almost all reactions of physiological importance.  Scientist have restricted the things that produce fermentation to a group called ferments that includes molds, bacteria and yeast.  People often use a yeast called brewerís yeast to make alcohol, and a yeast called bakerís yeast to make bread.  Pasteurization is a process to destroy harmful bacteria and fungi.  Heating the target liquid to 131-158 degrees does it.  A French chemist named Louis Pasteur invented this process.  He invented the process in 1865 to inhibit the process of fermentation in juice and milk, because if someone drank fermented juice or milk they could get sick or even die. 


 Yeast is a single celled fungus.  Ultraviolet light is a part of the electromagnetic spectrum. 



Ammireti, Joe F.,  ìFungiî World Book Encyclopedia, 1998 pp.  558-560 

Carter, Joseph L., Life Science: A Problem Solving Approach, Ginn and Company, 1971, pp. 170, 181-185

ìFermentationî Microsoft Encarta. 1994

Fraizer, Ralph, The Biological Sciences: Investigating Manís Environment, Laidlaw brothers, 1971 pp.93-95

Miller, Martin W.,  "Yeast,î World Book Encyclopedia, 1991 pp. 556-557 

ìPasteurizationî Microsoft Encarta. 1994 

Student Dictionary, Boston-New York, Houghton Mifflin, 1994, pp. 1081 

ìSugar Metabolismî Microsoft Encarta. 1994 

ìWhat is Ultraviolet Lightî, 1/22/97 

ì Yeast Information and Technique Resourceî 
Sept 8, 1993 

ìYeastî Microsoft Encarta. 1993


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