Optimal Amount of Yeast per 100g of Sugar for the Production of Alcohol
By Jamie Gant and Ari Hest
Introduction
What amount of yeast would produce the greatest amount of alcohol when combined with 100g of sugar? I hypothesized that the more yeast used, the greater amount of alcohol that would be produced. I also thought that there may be a point at which the addition of additional yeast would not do anything be cause it would not have any more sugar to ferment with.
Methods and Materials
To test my hypothesis I fermented 100g of sugar using three different amounts of yeast. I used 1g, 5g, and 10g yeast. 5g was what we started with in the class experiment with Mr. Reiblein. I thought that 5g may have been the most effective amount of yeast (any additional being useless) because that was what Mr. Reiblein started with, so I tested 10g of yeast to see if it would produce anymore alcohol than the 5g of yeast. I tested 1g of yeast just to see if perhaps the 5g of yeast was beyond the saturation point and thus the results from the 1g of yeast may have the same results as the 5g of yeast.
To set-up the fermentations we measured out 100g of yeast, 1g, 5g, or 10g of yeast, and 500mL of water, and put them into a soda bottle to ferment. We left them to ferment for a week so that we were sure that the fermenting process was complete.
Diagram of Bottle
After the solution was completely fermented we had to figure out how much alcohol was in the resulting fermentate. To do this we had to distill the fermentate. We distilled the fermentate by putting 250mL of the fermentate into the distilling apparatus.
Diagram of Distillation
Once the fermentate was distilled we had to calculate the amount of alcohol in the distillate. To do this we first had to calculate the density of the distillate. The density is the mass over the volume. Once we had the density we had to look at the chart of alcohol percentages in order to figure out how much alcohol was in the distillate. Once we had the percentage of alcohol we could figure out the number of grams of alcohol that were present. To get the number of grams of alcohol for 500mL of fermentate we then multiplied the result by two. Finally, we then were able to calculate the percentage of alcohol per 500mL of fermentate.
Results
We performed two trails of all three of amounts of yeast. In the two trials of the amounts of yeast, for all three amounts, we got very similar results which indicates that our results were probably fairly accurate.
For 1 gram of yeast we got that there was an average of .767% percent alcohol for 500mL of fermentate. For 5 grams of yeast we got that there was 9.433% more alcohol. The average was 10.2 % alcohol per 500mL of fermentate for the 5 grams of yeast. And finally for the 10 grams of yeast we got that there was 1.46% more alcohol than for the 5g of alcohol. The average was 11.66 % alcohol per 500mL of fermentate for the 10 grams of yeast.
Discussion
The 10g of yeast produced the greatest amount of alcohol followed by the 5g and the 1g of yeast, respectively. Even though there were 5g more of yeast in the 10g of yeast ferementate than in the 5g, there was not a very large difference, comparatively speaking, between the two fermentates. However, there was a very large difference in the percentage of alcohol between the 1g and 5g of yeast.
These results indicate to me that 5g of yeast is nearing the point at which any amount more of yeast would produce only a little more alcohol. This happens because there must be a point at which there is no more sugar left for the yeast to ferment with. I would expect that if there were more sugar in the solution the ³yeast saturation point² would be higher because there would be more sugar for the yeast to ferment with. There probably is an optimal yeast to sugar ratio for the production of alcohol.
Out of the three amounts of yeast that we tested, I think that the 5g of yeast was the most effective. Although 10g of yeast produced the greatest amount of alcohol, at double the amount of yeast it only produced a fraction of alcohol more than the 5g of yeast. At grams of alcohol that each gram of yeast produced, the 5g of yeast was the most efficient. For matters of conservation 10g of yeast is not practical. I imagine that if I performed more trials of even greater amounts of yeast I would not get very much more alcohol.
Conclusion
My hypothesis was correct. The more yeast that I used, the more alcohol that was produced. There was also a point at witch there seemed to be a ³yeast saturation,² where I think there was not enough sugar for the yeast to all completely ferment. Some where around 5g of yeast the solution seem to become saturated with yeast and the addition of additional yeast seemed to have a limited effect.
If I were to investigate this further, I would use a larger amounts of sugar and test to see if the yeast reaches a saturation point at a higher amount of yeast. I would expect that the saturation point would be higher because there would be more sugar for the yeast to react with.
I would also test increments of yeast between 5g and 10g with 100g of sugar to see if there is a point in between at which yeast seems to reach its saturation point.
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