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    Chemistry Activity
    Fermentation by Yeast

    Major Chemical Concept

    Fermentation is a process carried out by many microorganisms and which produces a variety of useful compounds. This chemical reaction can be investigated in terms of the various factors that affect the rate of a chemical reaction, including reactant concentration, stoichiometry, and temperature.
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      General Safety Guidelines
      Major Chemical Concept
      Level and Expected Student Background
      Time
      Safety
      Materials and Apparatus
      Advance Preparation
      Additional Teacher Resources
      Relevant National Science Education
      Standards
      Relevant New Jersey State Science
      Education Standards


    Level and Expected Student Background

    This activity is appropriate for basic, general, and honors students. Students should have the laboratory skills to accurately use a balance, graduated cylinder, and thermometer. Students also should be familiar with pH and the use of indicators. The ability to read and interpret balanced chemical equations is helpful.

    Time

    If the schedule provides a double period between 60 and 90 minutes, then this lab can be done without difficulty. If there are only 45-minute periods, then some preparation by you is necessary. This would include preparing water of different temperatures and possibly water of different pH if you does not think students are capable of making the chemical adjustments. If using only 45-minute periods, one period could would be devoted to weighing the required masses of sugar and yeast as well as the labeling of glassware. Additionally, students could prepare solutions of different pH.

    If there are no double periods, the lab can still be run in a 45-minute period to produce comparable results with some students keeping track of the lab beyond class time if that can be arranged. Students should be assigned to one of the setups rather than each pair doing all three variables.

    Safety

    General Safety Guidelines

    1. Read the Safety section in the student procedure.

    2. Be aware of the possibility of flasks slipping when balloons are attached to the neck of the flask. Students working in pairs should assist each other in this task.

    3. Spills of acetic acid should be neutralized with sodium bicarbonate solution (10% NaHCO3) or solid reagent before clean up.

    Materials (for 24 students working in pairs)

    • Baker's yeast (there are several different types including rapid; all work)
    • Sucrose (table sugar); an extension of this experiment would be to test other sugars such as fructose, glucose (dextrose), and lactose.
    • Sodium bicarbonate, NaHCO3, 100 g
    • 0.1 M Acetic acid solution (dilute 6 ml of concentrated HC2H3O2 to 1000 ml)
    • pH paper or universal indicator solution
    • 12 spatulas
    • 12 digital or alcohol thermometers (36 would be ideal)
    • 36 Erlenmeyer flasks, 125-ml volume
    • 24 beakers, 250 ml
    • 12 beakers, 600 ml
    • 6 balances
    • 36 tare containers for the yeast (small paper drinking cups)
    • 3 hot plates
    • Incubator or insulating material (Styrofoam cups large enough for 125-ml flasks)
    • 36 spherical balloons (fresh); test size of balloon neck by fitting on flask
    • 36 rubber bands
    • Masking tape
    • “Tape” measure material (calibrated paper strips, curling ribbon)
    • Timers

    If universal indicator is used rather than pH paper, the isopropyl alcohol present in the solution does not seem to affect the yeast's activity. Styrofoam cups large enough to accommodate a 125-ml flask may have to be placed in a large beaker to prevent tipping. Otherwise, secure the flask within the cup with a clamp and stand.

    An alternative to using balloons for gas collection and measurement is to set up a water displacement gas collecting system, using a 250-ml graduated cylinder for collecting and measuring the gas. Over a 90-minute period, gas volume can reach 250 ml.

    It is a useful exercise to have students graph their data. With the volumes collected in balloons, the graph of the data shows a curve over 90 minutes. With the data collected using water displacement and a graduated cylinder, the data graphed produces a straight line. Ask students to account for these differences (balloon leakage through the material, resistance to stretch as the balloon fills, other?)

    Advance Preparation

    1. If students do not have double periods and are confined to single class periods, time can be saved by advanced preparation of water at specified pH values. The same is true for the various temperatures of water prior to lab beginning.

    2. If using universal indicator, reference colors need to be available for the different pH values used in the experiment. Stock solutions at pH 2, 6, and 11 can be dispersed to students who can use spot plates and drops of universal indicator for their individual reference colors (white paper background is helpful).

    3. Test the pH paper to make sure it is not too old.

    4. Yeast can be dispensed in 10-g increments, using small paper cups.

    Additional Teacher Resources

    These original papers on fermentation by Louis Pasteur, Moritz Traube, and Eduard Buchner (fermentation without yeast cells) can be found at Carmen Giunta's Classic Chemistry, from Le Moyne College.

      Louis Pasteur (1822-1895): Experiments and New Views on the Nature of Fermentations

      Moritz Traube (1826-1894): On the Theory of Fermentation and Decay Phenomena, also of Ferment Activity in General

      Eduard Büchner (1860-1917): Alcoholic Fermentation without Yeast Cells. Preliminary Communication

    Relevant National Science Education Standards

      Unifying Concepts and Processes — The activity involves the interaction of components in a biochemical system, the use of evidence to draw conclusions, and the measurement of change.

      Science as Inquiry — The activity involves conducting systematic observations, interpreting and analyzing data, drawing conclusions, and communicating results.

      Physical Science — The activity is concerned with chemical reactions, conservation of energy, and increase in disorder.

      Life Science — The activity deals with the cell as well as the behavior of organisms, as well as matter, energy, and organization of living systems

      Science and Technology — The activity explores the science behind an important technology.

      History and Nature of Science — The activity illustrates the nature of scientific knowledge.

    Relevant New Jersey State Science Education Standards

      5.1 The activity involves conducting systematic observations, interpreting and
      analyzing data, drawing conclusions, and communicating results.
      5.4 The activity explores the science behind an important technology.
      5.5 The activity investigates a process carried out in living organisms.
      5.6 The activity discusses the biochemical behavior of sugars in living systems.

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