ROOT BEER
Introduction:
In this demonstration you will be observing the action of yeast on a mixture of
sugar, water, and flavorings through both aerobic and anaerobic respiration. The
yeast are microbes that will break down sugar into water and carbon dioxide--the
latter causing the root beer to become carbonated. The oxygen present will
eventually be depleted, causing the yeast to revert to anaerobic respiration. We
will be following aseptic technique and use only food-grade containers for this
experiment.
Materials:
Bottles--washed and sterilized
Wine corks or caps and crowns
Stirring spoon
Large (20 liter/5 gallon) enamel kettle or pot--DO NOT USE ALUMINUM!!
*59 ml Schillings root beer concentrate
*2.27 kg Sucrose (table sugar)
*19 l Chlorine-free water
*Containers to measure out needed volumes of materials--your choice--see
procedures
*9.5 g Yeast dissolved in 236 ml warm water
*see Caution 2. below
Cautions:
1. Wash hands thoroughly with antibacterial soap and water before and after
completing each step of the laboratory.
2. Alter the volumes and measures (by using proportions) to best suit your
needs.
3. Wear goggles and laboratory apron.
Procedure:
Day 1
1. Make sure all materials, equipment, and your hands are as clean as possible.
Wash hands before handling any materials.
2. Place sucrose and root beer extract into kettle
3. Gradually add chlorine free water
4. Add yeast/warm water mixture and stir well.
5. Immediately place mixture in clean/sterile bottles, leaving approximately a 5
cm airspace at the top.
6. Tightly cork or seal the bottles and place them on their sides in a warm (2530oC) location.
Day 2
• Record observations
Day 3
• Record observations
Day 4
• Once refrigerated, your root beer should be ready for consumption!!
Adapted from:
• Nancy Heitel, et. al., "Production of Home Brewed Root Beer," Mankato State
University, Mankato, MN, 1988
KIMCHEE:
Introduction:
Pickling is one of the most ancient forms of preserving food. You will be using
microbes to convert sugars into lactic acid. The microbe involved is called
lactobacilli. As the population of lactobacilli grows, they eat the natural sugars in
plant juices and produce lactic acid as a waste product. As the lactic acid levels
increase, so does the acidity. This highly acidic environment prevents the growth
of other bacteria that would under normal conditions feast on the food causing
spoilage. In this lab, you will be making kimchee and study lactic acid
fermentation.
Materials:
Chinese cabbage (cut into 5-7 cm chunks)
1 red hot chili pepper, chopped
2 cloves garlic, thinly sliced
non-iodized (pickling) salt
quart glass jar
plastic bag with water
pH indicator paper
small plastic pipette
Microscope slids
crystal violet stain
microscope
innoculating loop or tooth pick
Procedure:
Groups:
Group 1: use 1 tsp. salt
Group 2: use 2 tsp. salt
Group 3: use 3 tsp. salt
Day 1
1. Wash your hands thoroughly.
2. You will be using a glass jar and baggy filled with water to hold down the
cabbage.
3. Alternate layers of cabbage, garlic, pepper and sprinkling of salt in the jar.
Press each layer down firmly until the bottle is packed full.
4. Press down firmly on the top of the ingredients. Press down occasionally
until the end of class. When there is space, fit the plastic bag filled with
water into the jar, and tighten on the lid. Air should bubble out around the
edges of the cabbage when you press down. Check daily to make sure to
keep the cabbage covered by a layer of juice at all times.
5. You may need to add a small amount of clean water to keep the cabbage
under juice by the end of the hour.
6. Measure and record the acidity of the fresh juice on top each day with a
pH indicator paper.
Day ???
7. Place a drop of fresh juice on a microscope slide. Use the innoculating
loop to spread it around the middle 1/3 of the slide.
8. Let the slide air dry.
9. Quickly pass the slide through the flame of the Bunsen burner 3-4 times.
10. Let the slide cool.
11. Cover the slide with 2-3 drops of crystal violet.
12. After 30 seconds rinse the slide with water.
13. Examine the slide under the microscope and draw the bacteria.
14. When the pH drops to 3.5, your kim chee will be ready. (About 3-7 days)
Enjoy!
Cautions:
 When working with chili peppers, take care not to touch eyes or mouth. Wash
hands thoroughly when finished.
 Bottle used to ferment kim chee has been cleaned for you, do not open it until
you are ready to place the ingredients inside..
Questions:
1. What does the salt do to the cabbage?
2. How do you think the salt affects this fermentation?
3. Is lactobacillus a salt-tolerant microorganism?
4. Don't forget to draw and describe the bacteria found in your kimchee.
MAKING YOGURT
Introduction:
Yogurt production demonstrates fermentation by Streptococcus thermophilus
and Lactobacillus bulgaricus. Heated milk is innoculated and maintained at a
given temperature causing bacteria to grow and ferment lactose, the sugar in
milk. The bacteria produce lactic acid which causes the milk to coagulate and
adds a sour flavor. Be sure to follow aseptic technique and use only food-grade
containers for this experiment.
Materials:
quart glass jar
pH paper
Food grade thermometer
Microscope slides
Hotplate
Cooking pot
Innoculating loop (a toothpick will work)
2 cups milk
Crystal violet stain
1/3 cup nonfat dry milk
Microscope (oil immersion if available)
2 tablespoons plain yogurt
Procedure:
Groups:
Group 1 – whole milk
Group 2 – 2% milk
Group 3 – skim (nonfat) milk
1. Combine milk with nonfat dry milk and heat in a double boiler to 190° F.
Hold at that temperature for 10 to 20 minutes so that the protein in the milk
mixture will take up more water and make a better gel. Cool to 115° F
(warm) and record the pH of the mixture.
2. Place the plain yogurt in a jar and gradually blend in the warm milk.
3. Cover. Place in a slightly warm styrofoam cooler. The temperature within
the cooler should be about 110° to 120° F to provide optimum conditions
for yogurt culture activity.
4. Allow to stand undisturbed until the mixture is firm when the jar is gently
wiggled. This may take as long as 6 to 8 hours.
5. Record the pH of the yogurt.
6. Chill yogurt as soon as it is set. It can be stored in the refrigerator for up to
3 weeks.
7. Place a drop of water on the slide. Use the innoculating loop to mix a little
yogurt with the water and spread it around the middle 1/3 of the slide.
8. Let the slide air dry.
9. Quickly pass the slide through the flame of the Bunsen burner 3-4 times.
10. Let the slide cool.
11. Cover the slide with 2-3 drops of crystal violet.
12. After 30 seconds rinse the slide with water.
13. Examine the slide under the microscope and draw the bacteria.
14. Add 2 tablespoons sugar and 1/4 cup fresh, crushed or frozen fruit .
15. Taste your yogurt. (Do not eat any yogurt that smells or looks bad! If in
doubt, throw it out!)
Questions:
1. What effect does the milk fat have on the finished product?
2. What do you think would happen if we increased the amount of sugar in the
milk?
3. Why do you think we added the skim milk powder?
4. Don’t forget to draw and describe your bacteria.
Yeast Bread Investigation
Introduction:
Bread dough is usually leavened by bakers' yeast (actively gas-producing strains
of Saccharomyces cerevisiae ). Yeasts ferment the sugar in the dough,
producing ethanol and carbon dioxide. CO2 is the leavening agent and the
alcohol evaporates off during baking. Sometimes other gas-producing
microorganisms are involved in bread leavening--these usually are
heterofermenting lactic acid bacteria (sourdough bread or salt-rising bread)
Commercial yeast is prepared and sold in two forms: yeast cakes and active dry
yeasts. Yeast cakes contain, in addition to yeast cells, small amounts of starch,
vegetable oils, and some lactic acid bacteria. Active dry yeast is made by drying
the yeast cells to less than 80% moisture. These yeast cells are dried carefully at
low temperatures so the cells will survive. When these yeast cells are stored at
room temperature, they will retain their "dough-raising" ability for many months.
Materials
Bowl
Mixing spoon
Flour
Yeast or starter
Water
Sugar
Oil
Plastic wrap
Cookie sheet
Microscope slides
Crystal Violet Stain
Microscope
innoculating loop or tooth pick
Procedures
Group 1 - starter
1. Place ½ cup starter in bowl.
2. Add 11/2 cup flour and ¾ cup water.
3. Mix and add flour until dough is of correct consistency.
4. Let dough sit 5 min. While dough is sitting do the following.
5. Place a drop of water on a microscope slide.
6. Take a very small bit of starter and place it on a slide.
7. Use a tooth pick to mix the starter & water and spread it very thinly over the
middle of the slide.
8. Let the slide air dry.
9. Quickly pass the slide through the flame of the Bunsen burner 3-4 times.
10. Let the slide cool.
11. Cover the slide with 2-3 drops of crystal violet.
12. After 30 seconds rinse the slide with water.
13. Examine the slide under the microscope and draw the bacteria.
14. Back to the dough - Add 1 tsp. salt and mix.
15. Roll into sticks and let rise 5 min.
16. Cook at 425F for 15-20 min.
Groups 2&3 – rapid and regular yeast
1. Pour 1 cup warm water into bowl.
2. Dissolve yeast in bowl with warm water.
3. Place a drop of water on a microscope slide.
4. Take a very small bit of dissolved yeast and place it on a slide.
5. Use a tooth pick to mix the dissolved yeast & water and spread it very thinly
over the middle of the slide.
6. Let the slide air dry.
7. Quickly pass the slide through the flame of the Bunsen burner 3-4 times.
8. Let the slide cool.
9. Cover the slide with 2-3 drops of crystal violet.
10. After 30 seconds rinse the slide with water.
11. Examine the slide under the microscope and draw the bacteria.
12. Add 21/2 cups flour, 2 tbs. oil, 1 tsp. sugar, 1 tsp. salt.
13. Mix to combine.
14. Let dough sit 5 min.
15. Roll into stick and let rise 5 min.
16. Cook at 425F for 15-20 min.
Questions:
1. Describe and compare the three different types of bread sticks. Which one
rose the highest? Which one had the best consistency? Which one tasted the
best?
2. What factors can you think of that would effect how well the yeast rises?
3. The starter culture doesn't just have yeast in it. What do the other microbes
do?
4. Don't forget to draw and describe the microorganisms from your slide
preparation.
References
http://www.uwrf.edu/biotech/workshop/activity/act1/act1.pdf
http://www.waksmanfoundation.org/labs/csuchico/labs1998.html
http://www.bioteach.ubc.ca/Bioengineering/FoodMicrobiology/index.htm
http://www.accessexcellence.org/LC/SS/ferm_references.html