Instructor Information
JCE Classroom Activity: #30
Cabbage Patch Chemistry Background
Integrating the Activity into Your Curriculum This Activity involves students for an entire month (the fermentation period) in the National Chemistry Week 2000 kitchen chemistry theme. Related chemical concepts include organic chemistry, catalysts, and carbohydrates. Making sauerkraut has obvious home economics applications. History can also be a cross-curricular application, as fermenting cabbage and other vegetables has been important throughout history. For example, Chinese manuscripts tell of its use to feed laborers working on the Great Wall of China. The Activity ties in well with biology classes, where fermentation, lactic acid cycles, and plant cell morphology could be discussed in more detail. Additional activities illustrate the production of ethanol through fermentation of sugars in apples (2) and corn (3). A Web site contains 17 microbiology activities in Adobe Acrobat pdf format (4).
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About the Activity In this Activity, students make sauerkraut and also investigate the effect of changing one variable in the sauerkraut-making process. Multiple suggestions for variables to change are listed in step 8 on the Student Activity side. Instructors and students may think of additional variables. Cabbage takes about four weeks to ferment. It is recommended that students not eat their results from either the “regular” or “variation” jar. Although it is easy to prepare edible sauerkraut at home, this activity does not include the required safeguards. Students can taste store-bought sauerkraut instead and also compare its pH to that of their product. Students should monitor the jars for any unwanted yeast or mold growth during fermentation, skimming the liquid as necessary. To illustrate what happens to cabbage without fermentation, instructors may wish to have students leave pieces of cabbage inside a refrigerator as well as out on a counter. Non-iodized salt, which can be found in the grocery store as pickling or canning salt, should be used. The outer leaves of the cabbage can be removed if dirty or damaged, but don’t remove too many leaves as the organisms necessary for fermentation reside on the outside. The shredded cabbage must be held underneath an inch or two of salt solution for anaerobic fermentation to occur properly. Air bubbles should be removed by tapping the jar or by sliding a butter knife around the inner surface of the jar. The cabbage can be held down with a food-grade plastic lid cut to the proper size and a bent plastic straw. The jar should be capped loosely. A well-ventilated area is recommended, as the fermentation generates an odor. For best results, the jars should be out of direct sunlight at a temperature of 65–70 °F. The final product will reach a pH of 2–4, which students test with indicator paper. Alternatively, instructors may wish to have students titrate the juice with a base or test it with red cabbage juice indicator.
Answers to Questions 1. In the “regular” jar, the pH begins at a neutral value and drops to a final acidic value of 2–4. The appearance and odor of the fermented cabbage should be similar to those of store-bought sauerkraut, although the color may be darker. Results of the “variation” jar will depend on the variable changed. 2. The conditions needed for an effective sauerkraut fermentation are an anaerobic environment with a temperature of approximately 65–70 °F and a salt solution concentration of 2–3%. Conditions that inhibit the fermentation may vary, depending on which variable students change. 3. There is a stopping point for fermentation: when there are no more sugars for the bacteria to ferment. 4. Other fermented products include pickles, olives, kimchi, yogurt, cheese, certain alcoholic beverages, and gasohol.
This Classroom Activity Sheet may be reproduced for use in the subscriber’s classroom.
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Many vegetables need to be preserved to remain edible for long periods while kept at room temperature. One preservation method is fermentation. In the proper environment, microbial organisms present on the surface of particular vegetables convert sugars in the vegetable tissues to acids. The acids lower the pH and thereby inhibit the multiplication of organisms that would spoil the food. The fermenting organisms on cabbage are bacteria that produce lactic acid, carrying out the reaction in an anaerobic environment with an optimal salt concentration of 2–3%. The reaction, which is catalyzed by bacterial enzymes, produces lactic acid from glucose: C6H12O6 → 2CH3CH(OH)COOH. Specific details of the chemistry of making sauerkraut, as well as pickles, olives, and kimchi, are in a previous issue of JCE (1).
References and Additional Activities 1. Oberg, C. J.; Brown, R. J. J. Chem. Educ. 1993, 70, 653. 2. Borgford, C. L.; Summerlin, L. R. Chemical Activities Teacher Edition; American Chemical Society: Washington, DC, 1988; pp 212–214. 3. Maslowsky, E., Jr. J. Chem. Educ. 1983, 60, 752. 4. MicrobeWorld Activities. http://www.microbeworld.org/mlc/pages/activities.asp (accessed Sep 2000). JCE Classroom Activities are edited by Nancy S. Gettys and Erica K. Jacobsen
JChemEd.chem.wisc.edu • Vol. 77 No. 11 November 2000 • Journal of Chemical Education
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JCE Classroom Activity: #30
Student Activity
Cabbage Patch Chemistry Many is the time when the vegetable drawer of a refrigerator is opened only to have moldy, spoiled vegetables come to light! Left outside of the refrigerator, some vegetables spoil even faster. How can the shelf life of these vegetables be extended? Over 2000 years ago, fermentation was developed as a preservation method. Organisms found naturally on the surface of some vegetables, such as cabbage, can convert the sugars in the vegetable tissue into acids. The fermenting organisms on cabbage are bacteria that produce lactic acid. The bacteria carry out the reaction in an anaerobic (without air) environment. The reaction, catalyzed by bacterial enzymes, produces lactic acid from glucose: C6H12O6 → 2CH3CH(OH)COOH. The end product is called sauerkraut. In this activity, you will investigate the fermentation process by making sauerkraut, a process that will take about four weeks.
Try This Be Safe! Do not eat You will need: head of green cabbage large enough to give 2 cups shredded cabbage, sharp knife, butter knife, cutting board, non-iodized salt (canning or pickling salt), two your products. Dispose wide-mouth glass pint jars with lids, two disposable plastic lids from food containers, two of them as directed by flexible drinking straws, marker, scissors, water, measuring spoons and cups, bowl, spoon, your instructor. It is dropper, pH paper, materials for variation chosen in step 8, and potato masher (optional). possible to make edible __1. Label one wide-mouth glass pint jar “regular” and a second jar “variation”. sauerkraut. However, __2. Take a disposable plastic lid from a food container and trace around the mouth of one required safeguards are of the jars. With a scissors, cut out the circle marked on the lid. The circle should fit not included in this inside the jar and cover most of the top of the cabbage that will be packed into the jar. Activity. It will be slightly bigger than the opening of the jar, but you can bend it to fit over the cabbage. Repeat with a second lid. __3. Examine a head of green cabbage. Do you see any organisms on the leaves? Remove any damaged or dirty outer leaves. On a cutting board, cut the cabbage in quarters and cut out the white core. Shred one or more quarters into pieces about 1–2 millimeters thick (about the thickness of a quarter) so you have about 2 cups of cabbage. __4. Place 1 cup of the shredded cabbage in a bowl. Measure 3/4 teaspoon of non-iodized salt and sprinkle over the cabbage. Using clean hands or a potato masher, mix the salt and cabbage together, squeezing or mashing the cabbage to release some of its juices. __5. Place the salted cabbage into the jar labeled “regular”. Pack it down by pressing one of the plastic circles firmly on top of the cabbage. Leave the plastic circle in place. If you handled the salted cabbage with your hands, wash your hands before proceeding. __6. Measure 3/4 cup of water and pour into the “regular” jar. Tap the jar to dislodge any trapped air bubbles. If any visible bubbles remain, slide a butter knife along the outer edge of the inside of the jar to remove the bubbles. __7. Bend a flexible drinking straw at its “bend”. Place the short end of the straw flat on the surface of the plastic circle and trim off the excess straw at the long end so it fits into the jar and is also touching the surface of the plastic circle. Cap the jar loosely. __8. There are several possible changes for the “variation” jar: use more, less, or no salt; use iodized salt; add sugar; maintain samples at different temperatures; use microwaved cabbage; etc. You, or your teacher, may choose. __9. Repeat steps 4–7 for the “variation” jar, changing your chosen variable. Wash any utensils before reusing. __10. Leave the jars at room temperature, out of direct sunlight, for 4 weeks. Record observations daily, using the senses of smell and sight. Test the pH of the solution in the jars now and repeat the test every 7 days. Test by removing the lid and using a dropper to remove a few drops of liquid. Place the drops onto a strip of pH paper. Replace the lid. If cabbage floats to the top or if mold forms, remove the lid, skim the surface, discard the pieces, and replace the lid. __11. After 4 weeks, pick up a few pieces of cabbage from each jar to test its texture, odor, and appearance.
Questions __1. In each jar, what happens to the appearance, texture, and odor of the cabbage over time? What happens to the pH? __2. What conditions appear to promote the sauerkraut fermentation and what conditions inhibit or prevent it? __3. Is there a definite stopping point past which fermentation could not occur? Why/why not? __4. What other commercial products are produced by fermentation?
Information from the World Wide Web (accessed September 2000) 1. The Sauerkraut Page (includes a recipe for Chocolate Sauerkraut Cake). http://www.kitchenproject.com/html/sauer.html 2. The Origins of Kimchi. http://www.kimchikorea.net/english/html/part2-2/1.html 3. Fermentation. http://www.comptons.com/encyclopedia/ARTICLES/0050/00646912_A.html This Activity Sheet may be reproduced for use in the subscriber’s classroom.
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Journal of Chemical Education • Vol. 77 No. 11 November 2000 • JChemEd.chem.wisc.edu
