The Different Amounts of Alcohol Produced From Old and New Yeast
by Karen Robins
. Introduction
    I am trying to find out if there is a difference in the alcohol content of old and new yeast. I believe that the new yeast will contain more alcohol because it has not been around for as long a time as old yeast. Therefore it has not been exposed to as many elements in its surroundings and it has not lost any of its characteristics or abilities needed to produce alcohol.
Methods and Materials
    To start my experiment, I gathered up old yeast which had an expiration date of April 24, 1996 and new yeast which had an expiration date of July 8, 1997. I measured out 3 grams on the electric scale of both old and new yeast and put the measured contents into separate containers.

    I measured out 50 grams of sugar for each type of yeast and placed it in the separate containers. Next I measured two beakers full of 250ml of water. I then took two one-liter empty soda bottles and poured the combined mixtures for each experiment into each bottle and shook the contents up. The agitation caused the substance to produce carbon dioxide bubbles.

    Then I taped a little container to the side of the big bottle and put water into it. I attached a rubber stopper with a tube that was open to the side with the container full of water. This way as the substance produces carbon dioxide, it gets released into the water, but no air can come back in. During this beginning period of fermentation, I poured a small sample of the old yeast substance into a fermentation tube, covered up the opening with my thumb and turned it upside down to get the substance to the tube part in order to test if the old yeast would be productive. I let the bottles sit out for few days waiting for liquid substances to stop bubbling. When the bubbling had stopped, I set up the distillation part of my experiment. This next process would drive out the alcohol. The distillation set-up was composed of a long glass tube (the condenser) that had two openings for the entrance and exit of water by rubber tubing.

    Attached to one side of the condenser was the fermentate. A thermometer was placed on top of it to measure the temperature of the fermentate that was heated up by the heating mantle which was holding the fermentate flask. On the other side of the condenser was an empty flask that would collect the contents of the distillate. I poured approximately half of the contents from the fermentation tube into the fermentation flask. Next I heated it up to approximately 80°C. Afterwards I turned on the water and waited about a day until the distillation process was complete; a complete process was when there was distillate in the distillation flask. I then turned off the heat and water and detached the distillation flask from the set-up. I poured the contents of the distillation flask into a graduated cylinder and measured the volume. Finally I weighed the contents on the electric scale to get the mass. With the mass, volume, and the table of alcohol measurement, I did my calculations and found the percent of alcohol from the distillation. I did this process with both the old and new yeast contents.

Results
    The first part of my results was the side experiment that I did with the old yeast. I found that after a day, the old yeast had fermented, so I would be able to use the substance in the rest of my experiment.

    The next part of my experiment was waiting for the soda bottle substances to stop fermenting. It took about three days for both the old and new yeast substances to stop bubbling.

    The final part of my experiment was the distillation process. Here I had to set up the glass-ware, turn on the heat and water, and then wait for the experiment to produce results. The first trial run took a couple of days because the heat and water weren't always on for long periods of time. The second trial took about a day to complete. The table on the next page shows my calculations and the results of my experiment. The calculation results for the first trial run of the new yeast was 16.8ml and 14.5 grams. The alcohol content came out to 72%, but the actual pure alcohol content came out to 10.4 grams. The old yeast's calculation results for the first trial run was 15.5 ml and 13.3 grams. The alcohol content came out to 74%, but the actual pure alcohol content came out to 9.8 grams. For the second trial run, the new yeast weighed 17.2 grams and the volume was 19.3ml. The alcohol content came out to 71%, and the actual pure alcohol content was 12.2 grams. The old yeast weighed 16.0 grams and the volume was 18.5ml. The alcohol content came out to 74% and the actual pure alcohol content came out to 11.8 grams.

Discussion
    Throughout my experiment, I noted a number of things that didn't go the way that I had planned. I found that during the time that I was waiting for the soda bottles to finish fermenting, someone had knocked over the old yeast soda bottle. Even though the contents were fine because the rubber stopper was still intact, the side container that held the water, did not have any water in it. This may not have directly effected my experiment, but I'm sure that some air got inside the bottle because there was no water to block the air flow.

    During the distillation process, I did not properly measure out the amount of fermentate for the first trial. I only estimated about half the contents of the bottle instead of weighing it out on the scale. I realized later on that it worked itself out because I had the mass of the original contents and I weighed out the remainder of the substances that were left in the soda bottles for the second trial.

    Also when I did my trial runs, I only made one fermentate experiment, so I distilled from the same substance twice. I think that if I had the time, I could have made more than one trial of fermentate. Then I could have compared more substances and made more distillation trials.

    I believe that my results indicate some differences between old and new yeast. For example, in both trials, the old yeast produced a higher percentage of alcohol, but the new yeast had a larger amount of pure alcohol. But since both new and old yeast results were very similar, I don't believe that my experiment was conclusive enough to any new discoveries. I believe that if the age differences between the yeast's were ten years instead of about a year apart, I might have gotten results that would have been significant.

Conclusion
    It can be noted from this experiment, that there is no significant difference in alcohol content between old and new yeast. Even though the technical results showed that the new yeast produced more alcohol, there wasn't much of a difference between the two yeast's results to prove the hypothesis of my experiment.

    Further investigations that I might suggest for this experiment would be to produce more fermentation tubes, so that the distillation would be able to come from more than one source. Also I believe that using a wider variety of different aged yeast and different brands of yeast to test the alcohol content, might yield more conclusive results.

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