Fermentation:

Experiment Instructions (Demonstration)

LEARNING GOALS

By the end of this unit, you should be able to do the following:

1. Describe the purpose of fermentation in relation to glycolysis, NAD+, and NADH.
2. List the products of ethanol fermentation and lactic acid fermentation.
3. List common organisms that do each kind of fermentation.
4. List common foods created by each kind of fermentation.
5. Identify the Independent, Dependent, and Control Variables in your experiment.

Note - This experiment will take two or three hours to incubate, during which time you will need to change out the water in the bath every 30 minutes to keep a steady temperature. MATERIALS NEEDED

1 Packet of Bakers Yeast (sold on the flour and spices aisle of the grocery store) Table Sugar

Light Corn Syrup (ex. faro syrup)

Third Sugar Source (see below)

Medium Balloons (about 4 to 5 inches long when deflated, inflate to the size of a cantaloupe)

4 see-through, blank pill vials (ask to purchase blank ones from your pharmacist; they'll usually give them to you for free if you ask to buy them)

4 Quarters

Measuring Cups and Spoons

Tape (for labeling vials)

Marker or Pen (for labeling vials)

Clear Measuring Cup (with markings up the side, at least 1 cup volume)

Pot or Baking Dish Thermometer (optional)

Demonstration with a worksheet. You do not need to fill out an experiment tracking sheet for this lab.

You must take pictures of the experiments for your worksheet. You must have a card with your name visible in the picture.

FERMENTATION BY YEAST

**You WILL NOT write a lab report. However, you may wish to fill out an Experiment Tracking Sheet to aid in studying.**

Experiment #1 - Sugar Source

In this experiment, you will be testing the speed of fermentation in yeast using different sugar sources. Two of the sugar sources are specified for you. You will need to identify a third source. Ideas include artificial sweeteners, brown sugar, clear sodas (such as Sprite or Ginger Ale, shake out the carbonation first to make them "flat"), fruit juice, or even sweet tea! As you decide how much of the sweetener to use or whether to dilute sweet liquids, consider that the two stock solutions below include 45g of sugar per cup. Read labels and do your best!

1. Fill the pot or baking dish with 1 1/2 inches of warm water (30 °C or 86 °F, lukewarm bath water) to create a water bath. Change the water out every half hour to keep it warm.
2. (Identify Control Variables) In a separate cup (not your water bath), add 1 packet of bakers yeast to 1 cup of warm water. Stir for at least 1 minute. Set the cup in the warm water bath to keep the yeast warm.
3. In another separate cup, add 1/3 cup light corn syrup and 2/3 cup warm water. Stir for at least 1 minute. Place in the water bath.
4. In another cup, add 3 tsp of sugar to 1 cup of warm water. Stir for at least 1 minute. Place in the water bath.
5. In another cup, prepare a third sugar solution using warm water to dilute as necessary. Place in the water bath. (See instructions above for third sugar source.)
6. Give all solutions 30 minutes in warm water to come to the same

temperature. Change out the water bath with more warm water every 30 minutes throughout the experiment.

7. Label each vial with a different sugar source. Add one quarter to each pill vial to act as a weight. Add 4 teaspoons of the sugar source to each vial.
8. Fill the rest of each vial almost full with yeast solution. Cap and invert several times to mix.
9. (Identify Negative Control) Fill a fourth vial with the appropriate substances to make a negative control experiment.
10. Uncap all vials and stretch a balloon over the top. Make sure the balloon is mostly deflated. (Be careful, the "teeth" at the mouth of the vial will cut the balloon if you slide it across them.)
11. Place all vials in the warm water bath. Wait two hours, changing the water bath every 30 minutes. After two hours, some of the balloons should be inflated as below. You may continue to a third hour if you choose.

Measuring the Balloons

12. In a clear measuring cup, measure out 1/2 cup of water. (Many clear measuring cups have mL, or oz. markings. Use these if you have them as they provide a finer measurement.)
13. Twist the balloon at the top of a vial several turns. Invert the vial and place the balloon into the measuring cup, completely submerging it (adjust water in the cup as needed). Read the new volume in the cup. Subtract the initial volume from this to get the volume of gas in the balloon.

Conclusions - Which sugar source worked best for doing fermentation? Was it easier for the yeast to grow with table sugar (a dissacharride) or with corn syrup (a

monosaccharide)? What was the gas in the balloon? Can you smell any alcohol the yeast produced in this brief time?

Experiment #2 - Temperature

Repeat the experiment above with your highest-producing sugar and a negative

control. This time, don't use the warm water bath. Keep all liquids in the refrigerator for 30 minutes prior to the experiment and then keep them in the refrigerator throughout.

Conclusions - Does fermentation occur more quickly or more slowly in the refrigerator? How is this related to food storage?

NEXT STEPS Worksheet

The next item in this module is a worksheet. Paste one picture of your fermentation vials with balloons into this sheet, answer the questions, and submit through the Assignment found in this module. Be prepared to answer quiz questions about fermentation in general and specifically about this example of fermentation using yeast.

Insert a picture of your refrigerated fermentation vials below. (Remember to include a name card.)

Compare your sugar source in warm water to your refrigerated sample. (Hint — There should be a measured number for each sugar source!)

Independent Variable Dependent Variable

Control Variables

Volume       Volume Minus Negative Control

Cold Sugar

Cold Negative Control

Warm Sugar (copied from before)

Warm Negative Control

How did refrigeration affect fermentation?