Written by David T. Crowther PhD & John R. Cannon Ph.D.
If you were to look on the last page of Webster's New World Dictionary you would find the word Zymurgy. Zymurgy is defined as "the chemistry of fermentation, as applied in brewing etc." What is fermentation?? That is what this lab is all about.
Fermentation relates directly to the breakdown of complex molecules in organic compounds. This breakdown is caused by the action of enzymes. This general definition includes virtually all chemical reactions of physiological importance, and scientists today often restrict the term to the action of specific enzymes, called ferments, produced by minute organisms such as molds, bacteria, and yeasts.
Some of the more common examples of fermentation are like the lactate bacteria that are naturally found in milk which turn the lactose into lactic acid and make milk go sour or "bad." Another example of fermentation is when butter becomes rancid and butyric acid is formed. Another example is when wine turns to vinegar and forms acetic acid.
| However, the Kingdom Fungi, provides us with one of the most famous fermenters. Yeast is neither an animal nor a plant. "Yeasts are now defined as a group of about 160 species of single celled, microscopic fungi. Not all are useful: some cause spoilage of fruit and vegetables, some cause disease (for example , the fairly common "yeast infection" of Candida albicans). Most of the yeasts used in making bread and alcoholic drinks are members of the genus Saccharomyces, or "sugar fungi." (McGee, 1984 p.436) |  |
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Although yeast’s effects have been capitalized by humans since written records have been kept, and probably long before then, its true identity wasn't discovered until Louenhook invented the microscope and when Louis Pasteur found the bacterial rascals that had been plaguing the wine crops of France and then improved the process of wine making through a procedure now called pasteurization thus allowing yeast and only yeast to do the fermenting. Actually there is quite a nice story there, but for another day!! Yeast eats sugar - so to speak. Yeast is able to metabolize sugar (glucose) and break it down into ethanol with a natural by product of carbon dioxide. C6H12O6 Æ 2C2H5OH + 2CO2 + Energy Glucose Alcohol (Ethanol) Carbon Dioxide |
Essential to the yeasts’ production of alcohol is their ability to survive on very little oxygen, which most living cells use to burn fuel molecules for energy (remember the Krebs cycle!!). No oxygen is needed to complete the energy transfer of glucose to ethanol and CO2 as shown in the equation above. However, if this process is done in the presence of an abundance of oxygen the yeast cells convert the sugars completely to water and CO2. (McGee, 1984) (See equation below) Please note that no alcohol is made in this process thus explaining the reason we seal the bottles not only to capture the carbon dioxide, but also to end the redox cycle at the ethanol stage.
C6H12O6 + 6O2 Æ 6CO2 + 6H2O + Energy
Glucose + 6 Oxygen Æ 6 Carbon Dioxide + 6 Water + Energy
Although this scientific knowledge was not known until the field of microbiology took hold in the mid 1830's, you can imagine one day when an early Egyptian harvested grain, then mashed the grain and mixed in with a little water in order to use in it a meal - then was called away for a period of time. Upon return the mash was found bubbling and giving off an interesting odor. Not to be wasteful the mash was used in making what previously was very flat and uneventful bread, thus produced a light and fluffy, not to mention flavorful, bread that was very different than had been made before. Although this is not a true story, one could imagine that since natural yeasts have been around longer than humans, it would be safe to say that when humans finally got around to being thinking and experimenting folk, yeast was discovered with all of its wonderful benefits. It is said that the first real domesticated fermentation took place around 10,000 years ago when some honey was left or stored for a week or two and produced a beverage consumed in quantity by the Vikings. Now perhaps, this same individual (Egyptian or Viking) who discovered the bread slurry or bubbling honey mixture also decided to drink some of the slurry after a period of time - after a few slugs this person was feeling rather fine - but different than anything felt before?? Thus the intoxicating influence of the ethanol that yeast breaks the glucose down into. The rest is history - so to speak!! Grape skins naturally carry a yeast on them - squeeze a few grapes and leave the juice for a while - you get wine.
| Even our avian friends enjoy the fermentation process - just observe an American Robin Redbreast (Turdus migratorius) for a meal of Pyrocantha berries - at first it is just a social thing, squawking and a little feather ruffling - then it gets serious when it is time to fly home and the intoxicating effects of the berries severely influence the birds ability to fly home - designated flyers should be mandatory at each Pyrocantha bush!! |  |
McGee, Harold (1984). On Food and Cooking; the Science and Lore of the Kitchen. Collier Books & Macmillan Publishing Co. New York, NY.
Selinger, Ben (1994) Chemistry in the Marketplace. 4th Edition. Harcourt Brace. Sydney, Australia.
FAnyway, so much for a little fun background - what are we going to do?? I have been thinking that yeast takes both natural and processed sugars and has this uncanny ability to break it down into ethanol with a by product of carbon dioxide gas. Wouldn't yeast then be a great indicator of both how much and what kind of sugar is found in cereal?? Sounds like a research questions to me!!
Yeastie Beasties Activity
Materials:
Engagement: From your new bread maker that you got for a present several years ago - but only used once!! - Make a loaf of bread with yeast and one without yeast. Show to children and ask what they think is the difference. Use a directed questioning strategy to explore that one
"raised" and the other did not. Briefly explain that yeast allows for bread to rise by breaking down the glucose in the flower and giving off a by product of carbon dioxide.
Have a batch of yeast that has been sitting in warm water for about 5 minutes and allow the children to pass it around and make some observations.
Objective: By the end of the lesson the students will be able to recognize that yeast breaks down sugar and creates bubbles of carbon dioxide. Students will demonstrate through experimentation that natural sugars and processed sugars each react differently in the yeast fermentation process
by collecting and measuring the carbon dioxide produced from the yeast from several different cereals.
Experimentation:
1) Have each student select a mini box of cereal. Instruct them to not eat it!!
2) Have the students record all of the nutritional data, sugar in grams, weight of cereal and any other identifying characteristics that may seem relevant to further exploration during or after the experiment.
3) have each student smash the cereal into a granular powder form.
4) Place the mashed cereal into a Ziplock baggie
5) add 1 Tablespoon yeast.
6) add 1 cup water
7) Exhaust all remaining air and zip baggie (note red and blue make purple!!) Then swirl for 15 seconds.
8) Observe for up to 3 hours (or longer if necessary). Record how many times the baggie seal is popped and then if the baggie fills one quarter, one half, three quarters, or full without popping. Note that some of the newer and stronger sealing bags will not pop open. If this is the case - when the bag has reached maximum capacity have the children release the air and reseal the bag for further observations.
9) After all fermentation processes have concluded. Collect and analyze data - some of our original hypotheses may have been wrong??
Explanation: Allow the students to do research on yeast and fermentation. Students will discover the use of yeast in the process of making various beverages. Include that yeast is in the Kingdom Fungi and has properties of both animals and plants. Yeast has stages of resting, budding, and sporing.
Evaluation: Although formative evaluation takes place throughout the process of doing this lesson in the form of making products, one could build some formal evaluations into the lesson depending upon the desired outcomes for the individual teacher. Some formative or even summative assessments could be in the form of journal writing, research reports, role playing the historical developments of Zymurgy, etc.
Making Rootbeer with Dry Ice:
The dry ice way of making rootbeer is very simple - go to the grocery store and buy the Schilling brand of Rootbeer Extract. (I believe that they have 2 recipes on the side of the container??) Anyway, Here is how we do it:
Combine the sugar and RB extract together in a bowl making a heavy syrup (you will need to add water to get to the right consistancy)
Fill a 5 gallon water cooler to the 4 gallon mark.
Pour rootbeer syrup into the 4 gallons of water.
Add 1 oz of vanilla (to taste)
Break up about 2 lbs of dry ice and put gently into the cooler - quickly put the lid on the cooler with ventilation. DO NOT SCREW THE LID ON! (ALLOW THE COOLER TO VENT.)
You may add more sugar and/or vanilla to taste at this time.
Depending on the amount of carbonation desired and the length of time needed to carbonate the mixture - add dry ice as necessary.
We have found that using 5 - 6 lbs over about 1/2 hour and then letting that go for about an hour (total time 1 - 1/2 hour) gives a nice (not heavy) carbonation.
Best of luck with your project -