Yeasts are eukaryotic, single-celled microorganisms that belong to the fungal kingdom. When yeasts consume sugar and convert it to energy, they emit carbon dioxide, this is referred to as fermentation. The yeast will be more active and develop faster if there is more sugar present. While sugar and other sweets provide “food” for yeast, too much sugar can harm it by draining moisture from it and preventing it from growing. Too much sugar also delays the development of gluten. Increase the amount of yeast in the recipe or find a comparable recipe with less sugar.

Sweet yeast doughs will rise more slowly. Fermentation is sped up by a small amount of sugar, up to 3%. Warm water makes yeast grow, cold water has the reverse effect, and hot water kills yeast. Temperatures ranging from 0 to 47 degrees Celsius are suitable for yeast growth. Yeasts flourish in acidic settings with pH levels between 4.0 and 4.5. They can grow in lower pH environments than other bacteria, but not in alkaline environments. Yeasts are common in nature and can be found on grapes and other fruits. All yeast need food, moisture, and a controlled temperature environment in order to ferment. Its byproducts from food consumption include carbon dioxide, alcohol, and other organic molecules.


comparing yeast growth at various sugar concentrations.


  1. Two water bottles
    • 50ml of water
    • Yeast
    • Sugar
    • Two balloons
    • Sugar

(funnel may be needed to safely transfer the ingredients into the water bottles)


  1. A kettle was used to boil the water, then cold water was added to the boiling water to get lukewarm water.
  2. 50ml of lukewarm water was added to each bottle.
  3. ¼ teaspoon of table sugar was then added to the first water bottle, then ½ teaspoon of table sugar was added to the other water bottle.
  4. ½ teaspoon of rapid-rise yeast was then added to each solution and mixed.
  5. After mixing, a balloon was placed on each water bottle/ tube and sealed securely.
  6. The contents were mixed periodically.

(N.B- A string may be used to seal the balloon placed on water bottles).


15 MIN (INITIAL)highlow
30 MINhighlow
45 MIN (FINAL)highlowest
15 MIN (INITIAL)11 cm6.1 cm
30 MIN15 cm10.3 cm
45 MIN (FINAL)19.4 cm12.5 cm


During the experiment, 500ml water bottles were used. Then 50ml of lukewarm water was added to each bottle, after that, ½ teaspoon of sugar was added to the 1st bottle then ¼ teaspoon of sugar was added to the 2nd bottle. Finally, ½ teaspoon of rapid-rise yeast was added to both bottles, then the balloons were placed on each tube and securely sealed. The balloons were checked at the time interval of 15min to observe any changes, when glancing at the balloons, it was noticed that the balloons were getting bigger and bigger every time on top of the water bottles. Warmth and moisture are necessary for yeast to function, that is why lukewarm water was added. Sugar was converted to carbon dioxide by yeast.


Some bubbles were also observed in the yeast mixture during the experiment, it was the small carbon dioxide gas bubbles produced by the yeast as it “ate” the sugar.

As the yeast continued to react, additional sugar was transformed into carbon dioxide gas. The balloons were filled with this gas, which caused them to inflate. It was also observed that the balloon on the water bottle that had ½ teaspoon of sugar was growing bigger at a faster rate than the one that had ¼ teaspoon of sugar.

This can show that glucose concentration increases fermentation production in yeast. The more sugar present, the more active the yeast becomes, and the faster it grows. The balloon on the bottle that had less sugar was growing at a slow rate compared to the other one, even had fewer bubbles visible. It was seen that the concentration of sugar plays a vital role in the rate of fermentation, the more sugar present, the more active the yeast becomes, and the faster it grows. This also showed why the fermentation rates of the sugars differ over time. Both balloons grew until they reached a point where they grew no more.

During the experiment, when the balloons were growing bigger and bigger, using the time interval of 15 minutes, the circumferences of the balloons were measured. From the measurements, it can be safely concluded that the balloon on the water bottle with ½ teaspoon of sugar grew bigger and faster than the one on the water bottle with ¼ teaspoon of sugar. Another thing observed is that as time went by the fermentation rate of both the balloons started to decrease.


From what was observed during the practice of the experiment, it can be concluded that the more sugar there is, the more active the yeast will be and the faster its growth. THIS CAN BE APPLIED IN REAL LIFE: fermentation can be used to preserve food, preventing rotting or harmful microorganisms from growing in the food. Can also apply when baking bread.

author avatar
William Anderson (Schoolworkhelper Editorial Team)
William completed his Bachelor of Science and Master of Arts in 2013. He current serves as a lecturer, tutor and freelance writer. In his spare time, he enjoys reading, walking his dog and parasailing. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0

1 Comment

  1. I would like to cite this article for a research paper, would it be possible to disclose the authors name(s), and date this was published?

Leave a Reply

Your email address will not be published. Required fields are marked *

Post comment