1	Yeast and Alcohol Production - A Brewer’s Guide Fungi for the Fun Guy!
2	Abstract The amount of alcohol produced by various yeast species was studied. Four species of yeast- Saccharomyces cerevisae, Saccharomyces bayanus, Saccharomyces calbergensis and Saccharomyces pastorianus- were fermented for 32 days in sterile 400g/L sucrose and 0.67 g/L yeast nutrient solutions. Air locks vented the gasses and prevented contamination by external microbes. The specific gravities of the solutions were measured with a Hydrometer at 1, 11, 18 and 32 days after the yeast was added to the nutrient solution. The specific gravity was then used to calculate the alcohol content measured in percent of the total volume. Saccharomyces cerevisae was found to produce the most alcohol during the 32 day period (6.7% v/v,) whereas Saccharomyces pastorianus, a sherry yeast, produced the least alcohol (4.7% v/v.) Implications for wine and beer making were suggested.
3	Hypothesis If sugar is fermented using different strains of yeast, then some strains of yeast will produce alcohol more efficiently than other yeast strains because there are genetic differences in different yeast strains that have developed over time during the evolution of yeast.
4	Prediction I think the sherry yeast (Saccharomyces pastorianus) will produce the most alcohol because it is called a “Sherry” fermenting yeast and “Sherry” wines are of higher alcohol content (18 - 20 %).
5	Variables and Controls Manipulated Variable: Kind of Yeast used (Saccharomyces pastorianus, Sacchoromyces bayanus, Saccharaomyces cervesiae, Sacchormyces calbergensis) Responding Variable: Percentage of Alcohol produced Controlled Variables: Amount of Sugar used, type of Sugar, same time to ferment, same concentration of Sugar in solution, same temperature to ferment, same hydrometer used to measure specific gravity before and after fermentation Control Group 1: Sugar solution without Yeast added (yeast nutrient added only) Control Group 2: Sugar solution without Yeast or Yeast Nutrient added
6	Materials Table sugar (sucrose) Distilled water Different strains of yeast Saccharomyces pastorianus Sacchoromyces bayanus Saccharaomyces cervesiae Sacchormyces calbergensis Air-locks Campden tablets Yeast nutrient medium- (NH₄)₂HPO_4(aq) Fermentation containers Hydrometer
7	Procedure 1. Sterilize the bottles by washing with boiling water and rinsing with hydrogen peroxide. 2. Put water into each airlock and place a Campden tablet in the airlock to sterilize it. 3. Fill each bottle with 3 litres of water. 4. Add 1200 grams of sugar to each bottle. 5. Stir and shake well. 6. Add 1 gram of yeast to each bottle - using four different kinds of yeast in four different bottles. 7. Keep two bottles for controls. Add no yeast to them. 8. Add 1 ½ grams of nutrient to each of the four bottles. 9. Add 1 ½ grams of nutrient to one of the control bottles. 10. Put caps on the bottles and shake well to mix. 11. Take caps off and put airlocks on. 12. Leave the bottles at room temperature. 13. Observe every day. 14. Measure the specific gravity on day 1, on day 11, on day 18, and on day 32. Record all results as well as qualitative observations for those days. Stir each solution for 2 minutes before measuring the specific gravity to ensure that gas bubbles do not affect the specific gravity reading. 15. Calculate the percent of alcohol (ethanol) produced using the table and method that comes with the hydrometer.
8	Picture Gallery
9	Yeast Cells
10	Qualitative Observations and Data
11	Quantitative Observations and Data
12	Analysis and Discussion Specific Gravity readings were taken with a hydrometer on days 1, 11, 18 and 32. Using a commercial conversion scale, the % of alcohol was calculated. S. cerevisiae yeast produced the most alcohol ( 6.70 %)and the S. pastorianus produced the least alcohol (4.70 %). S. cerevisiae is often used for making wines and although S. pastorianus was labelled as a “sherry” yeast it did not produce as much alcohol in 32 days. My prediction was incorrect but my hypothesis was correct.
13	Further Discussion The fact S. pastorianus did not produce as much alcohol in 32 days could be explained by the fact that it may be a slow fermenting yeast and may need to take more time to produce its maximum alcohol. S. calbergensis is usually used in the brewing of beer and ales and will probably not produce a lot of alcohol. After 18 days the alcohol produced remained mostly the same. The sediment on the bottom of each of the four bottles containing yeast and Control 1 was probably caused by the yeast nutrient settling out and also dead yeast cells (first four bottles also had dead yeast cells in them). The air traps prevented oxygen from coming in and kept bacteria, molds, and other stuff out. If oxygen had gotten in, the alcohol could have been changed into vinegar (ethanoic acid).The Captan tablets in the air traps sterilized the water and prevented unwanted organisms from contaminating the bottles. The appearance of alcohol seemingly produced in Control 1 can be attributed to either some contamination by natural yeast spores found in our house or error in the technique of taking the specific gravity readings. The kind of yeast used did affect the color (S. cerevisiae) remained more whitish than the other three fermenting solutions. Each kind of yeast seems to have a slightly different way of fermenting sugars. This is probably due to the kind of genetics of each and the kind of enzymes they produce.
14	Experimental Errors The main experimental error was reading the Hydrometer correctly. The “meniscus” was hard to read at times and I might have misread the specific gravity readings that seem to conclude that some alcohol was produced in the control bottles. No air bubbles were seen to rise in the control bottles and I conclude that no alcohol was produced by fermentation. Therefore, most likely my readings are probably +/- 0.020 % off in the specific gravity and the amount of alcohol produced. Another error could have been in measuring the amount of water mixed with the sugar. I did not have a large graduated cylinder or “volumetric flasks” and used a kitchen measuring cup to measure the amount of water used to dissolve the sugar in. So, concentration may have been different - at least a little. Another problem with my experiment was that I didn’t have enough samples. I should have repeated the procedure more times to get more readings. I should have used more smaller jars instead of the big gallon jars but I didn’t have any. As it was the materials were very expensive so I couldn’t really have got more.
15	Conclusion From the data in the experiment we can conclude that the type of yeast will affect the wine/beer produced at least as to the likely alcohol content. Each kind of yeast produced a different amount of alcohol. Also, the smell and color was different in the types of yeast used. However, the quality of the beer or wine produced is most likely caused by what else is used to make the product. The type of grape for wine as well how the vintner makes the wine is important. The water, the kind of hops and barley malt used by the brew master are also important. Maybe, beverage brewing is more of an art than a science although science does play an important part too. Many universities such as the Ludwig Maximilian University in Munich and the University of California, Davis are involved in researching yeast and ways of making beer and wines.
16	Some Thoughts This was a lot of work but very interesting. I learned a lot of stuff about wine and beer making and about yeast and how it ferments sugars. Science projects like this take a lot of work and time but are fun!!
17	References “BarrelHouse Brewing: Yeast,” retrieved from the internet January 29, 2004 Berry, C.J.J., First Steps in Winemaking, Holmes and Sons, 1990 “Fermentation” Columbia Encyclopaedia 6th edition, 2001 retrieved from the internet January 27, 2004 “Fermentation” World Book Encyclopaedia, 2000 Homebrewing UK: “Glossary of terms,” retrieved from the internet January 29, 2004 Homemade Wine Tutorial: A Step-by-Step Guide to Making Your First Wine, Retrieved from the Internet January 27, 2004 Kunath, Brian, Fearless Brewing: The Beer Maker’s Bible, Firefly Books, 1998 Mathewson, S.W.,The Manual for the Home and Farm Production of Alcohol Fuel, retrieved from the internet February 1, 2004 journeytoforever.org/.../ethanol_manual/ z-image/fig5-1.jpg http://journeytoforever.org/biofuel_library/ethanol_manual/z-image/fig5-1.jpgNASA, “Planets in a Bottle: More about Yeast,” retrieved from the internet January 29, 2004 Nowicki, Diane and Ryan Leirmann, “Yeast Images,” retrieved from the internet January 29, 2004 Pambianchi, Daniel, Techniques in Home Winemaking: A Practical Guide to Making Château-Style Wines ,Véhicule Press, 1999 Saccharamyces Genome Database, retrieved from the internet January 30, 2004 Brewing.htm “The Wonderful World of Yeast!” retrieved from the internet January 29, 2004