Objective

To determine if the type of sugar used in yeast fermentation affects fermentation rate.   

Background

Yeast (Saccharomyces cerevisiae) is a single-celled microorganism used in the production of bread and alcoholic beverages. It is a facultative anaerobe that ferments sugars to make carbon dioxide and ethanol. Facultative means that it can grow whether oxygen is present or not. Faster rate of fermentation can be measured by how fast carbon dioxide and ethanol are produced. In this lab, you will use changes in volume as an index of carbon dioxide production.

Materials

  1. 100 g digital scale
  2. Spatula
  3. Weight boat
  4. Yeast
  5. Hot water bath with water held at 37oC
  6. Sugars
    • Dextrose
    • Sucrose
    • Maltose
    • Fructose
    • Lactose
    • Galactose

Procedure

  1. Collect a 100 ml measuring cylinder
  2. Use the digital scale to weight 2 grams of yeast and 2 grams of the sugar assigned to your group  
  3. Add yeast and sugar to the 100 ml measuring cylinder
  4. Add warm water (37oC) to the measuring cylinder and bring the volume to 50 ml
  5. Observe, read, and record the volume every 5 minutes for 20 minutes (terminate the experiment if the volume exceeds the 100 ml mark at any time before the 20 minutes is up)   
  6. Repeat the procedure
  7. Take the mean (average) of your two repetitions and report it using the table below (Note: Make sure to also collect data from the other groups)
 0 min5 min10 min15 min20 min
Dextrose Rep 1 (ml)50    
Dextrose Rep 2 (ml)50    
Galactose Rep 1 (ml)50    
Galactose Rep 2 (ml)50    
Sucrose Rep 1 (ml)50    
Sucrose Rep 2 (ml)50    
Maltose rep 1 (ml)50    
Maltose Rep 2 (ml)50    
Lactose Rep 1 (ml)50    
Lactose Rep 2 (ml)50    
Fructose Rep 1 (ml)50    
Fructose Rep 2 (ml)50    

Fermentation Data Collected From Groups

Lab Questions (18 Points)

  1. Create a line chart showing volume (ml) versus time (min) (make sure to label your graph). Represent the data for all five sugars on the same chart. (10 points)
  2. Based on the chart, list the sugars in order of decreasing fermentability rate (2 point)
  3. Provide what you think is the best explanation as to why the yeast ferment some sugars better than others (3 points)
  4. List at least 3 other factors that could affect fermentation rate other than sugar type in this experiment (3 points)
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Courtney Simons
Courtney Simons
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Courtney Simons is a food science professor. He holds a BS degree in food science and a Ph.D. in cereal science from North Dakota State University.