IB Biology Internal Assessment: Yeast Fermentation Rates Planning(a) Question- Growth: What is the effect on Yeast Growth/Expansion during fermentation when mixed in water of varying temperatures? Hypothesis- Temperatures above or below the recommended fermentation temperatures will contain less, or be void of growth, either due to inactivation or to yeast death. Variables- | | | | | | |Dependent Variables |Temp|Degrees F | |90 Degrees F-130 Degrees F | | | |erat| | | | | | |ure | | | | | | |of | | | | | | |wate| | | | | | |r. | | | | |Fermentation | |Hours | |Level of |Digital Timer| |time | | | |expansion | | | | | | |after other | | | | | | |variables | | |90 |75mL |75mL |75mL |N/A |N/A | |100 |105mL |75mL |N/A |N/A |N/A | |110 |85mL |75mL |75mL |N/A |N/A | |120 |125mL |75mL |N/A |N/A |N/A | |130 |75mL |75mL |N/A |N/A |N/A | Data Processing and Presentation- Overview- Yeast is a living substance. It is commonly used to rise bread, or to make alcohol, in a process known as Alcoholic Fermentation in which it releases oxygen. Through my research, I learned that during fermentation, the temperature is a very important factor in yeast expansion, as under 100 degrees, the yeast may not activate, while high temperatures will effectively kill your yeast, rendering it useless. My Lab Experiment served to test the effect of temperature on yeast expansion during fermentation. Presentation- Temperature |Repeat | |Volume Change | |90 | |1 | |0mL | | | | |2 | |0mL | | | | |3 | |0mL | | | | |4 | |N/A | | | | |5 | |N/A | | |100 | |1 | |30mL | | | | |2 | |0mL | | | | |3 | |N/A | | | | |4 | |N/A | | | | |5 | |N/A | | |110 | |1 | |10mL | | | | |2 | |0mL | | | | |3 | |N/A | | | | |4 | |N/A | | | | |5 | |N/A | | |120 | |1 | |50mL | | | | |2 | |0mL | | | | |3 | |N/A | | | | |4 | |N/A | | | |5 | |N/A | | |130 | |1 | |0mL | | | | |2 | |0mL | | | | |3 | |N/A | | | | |4 | |N/A | | | | |5 | |N/A | | | | | | | | | Yeast Expansion Conclusion and Evaluation- Conclusion- As is shown by my data, after the first trial at each temperature, the yeast refused to rise. This is due to temperatures effect on yeast, as a living thing. After completing the first five trials and ending my experiment for the day, I placed the jar of active dry yeast in the fridge where, due to prolonged exposure to such low temperatures, the whole jar died.
After frustratingly watching the next seven trials yield no rise in the yeast, I came to the realization that the cold of the fridge killed my yeast. This was just as much a surprise (as the jar said “refrigerate after opening”), as it was an interesting basis for my lab. Because my Lab was about Temperature’s effect on yeast expansion and growth, this death provides a good conclusion, as it shows that prolonged exposure to extreme cold(around 58 Degrees F in my fridge), effectively kills the yeast, just as exposure to extreme heat does. At the 90 Degrees of trial 1, the yeast simply was not activated, but at 130 degrees, it also didn’t activate.
Because temperatures below 130(save 90) activated it, I assumed that this was the temperature that kills yeast, just as 58 Degrees does. Limitations of experimental design- Many aspects of my project did not work very well and could have been improved in order to make for a better experimental design. For instance, instead of simply placing the yeast in water, I could have made dough, and placed it in the oven at different temperatures, making for a much more stable environment and temperature. Also, completing all 25 trials would have yielded better results as to what temperature truly leads to the greatest expansion by the yeast during fermentation. ———————– [pic]