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MIXED-PLATE BIOLOGY, HAWAIIAN STYLE: KIM CHEE FERMENTATION


Submitted by: Jeanine Nakakura
Kaimuki High School
Honolulu, HI


INTRODUCTION:
The Korean government named kim chee (or kimchi) a national treasure. A basic recipe for kim chee consists of vegetables pickled in a solution of garlic, salt, and red chili peppers. It is eaten year-round for its spicy taste and because it contains lots of vitamins C and B. In earlier times, during the fall, women made enough kim chee to last until early spring. In the winter, the kim chee would be buried in the ground, where it was warm, to keep it from freezing. Kim chee, also featured in Korean art, is stored outside in large clay jars called tokes , which are supposed to make kim chee taste delicious. Kim chee is ubiquitous in Hawaii and my students say that it is "ono" (Hawaiian for delicious) with hot rice.

TOPICS: fermentation, beneficial properties of foods, food preservation, diffusion and osmosis, pH

MATERIALS (basic recipe--enough for 6 groups):


  • 12 plastic ziploc-type bags (small)
  • 1 2-3 lb head of Chinese cabbage (Brassica rapa ), also known as "won bok", "nappa" or "petsai"; cut into 4-cm chunks
  • chopped red chili pepper or chili powder (not the type to make chili; amount depends on your tolerance for spiciness)
  • 3 cloves garlic, thinly sliced
  • 20 grams (3 tsp) non-iodized (pickling or kosher) salt
  • pH paper or red cabbage juice (to test pH)

PROCEDURE:

  1. Put one ziploc bag into another (to prevent leakage and odors). Layer 1/6 of the cabbage, 1/2 of a garlic clove, chili pepper (to taste) and 3.3 grams (1/2 tsp) of salt into the ziploc bags. Shake the bag to distribute the salt and other ingredients.

  2. Press down occasionally over the next hour.

  3. In a few hours, the cabbage should release water and shrink in volume by 1/3 to 1/2. Make sure the cabbage is covered by juice at all times to prevent microbes from growing. Leave out in a cool, well-ventilated (the smell can be quite strong) place for 2-3 days and then refrigerate. When the pH drops to about 3.5, (about 2 days to 2 weeks, depending on the temperature) the kim chee is ready to eat. If the kim chee tastes too salty, dilute with water.

DISCUSSION AND QUESTIONS:
Fermentation refers to the activity of bacteria and fungi. These microbes break complex compounds, like sugars, into simple substances, such as carbon dioxide and alcohol. Because these simple substances are toxic to food-spoiling microbes, they act as natural preservatives for food.

Before refrigeration, fermentation was a primary method of food preservation. Builders working on China's Great Wall ate cabbage fermented in wine. Ghengis Kahn's armies carried pickled food with them on their invasions of eastern Europe in the 12th century. In the early 18th century, the British Navy carried pickled cabbage to provide sailors with vitamin C to prevent scurvy.

You can't see microbes without a microscope, but you can see, smell and taste evidence of their activity. You want the cabbage to be covered by the juice so that it is kept from contact with the air. You are cultivating anaerobes (Lactobacillus ), organisms that grow best where there is no oxygen. Salt helps to release water and sugars from the cabbage cells. Lactobacillus uses the sugars and makes lactic acid. The more lactic acid produced, the lower the pH. When you expose the bag's contents to air, however, you are allowing different kinds of microbes to grow and that is why you must refrigerate the kim chee after 3 days. As you press down on the cabbage, ;you will see bubbles of carbon dioxide rising to the surface.

The warmer it is, the faster the kim chee ferments. If your classroom is a steady 25 degrees C (75 degrees F) or more, you can have kim chee within two days. Measure the acidity of the kim chee juice daily with pH paper or red cabbage juice. The kim chee is ready to eat when the pH drops from 6.5 to 3.5 (or when it tastes good to you!). With the red cabbage juice, a pH of 3.5 is a reddish-purple color.

Questions to think about:

  1. What is fermentation?
  2. What are 3 fermented foods you eat?
  3. Why was fermentation important in history?
  4. Where does the carbon dioxide gas in the kim chee come from?
  5. Why does the cabbage in the kim chee shrink and lose water?
  6. Why do we use salt to make kim chee?
  7. Why is Lactobacillus important in making kim chee?
  8. Why does the pH of the kim chee drop?
  9. Why should you refrigerate the kim chee after 3 days?
  10. Why do you want to keep the kim chee covered by liquid at all times?
  11. What are some beneficial (good) properties of chili peppers? garlic?


EXTENSIONS:
There are many varieties of kim chee -- experiment with different recipes. Explore other uses of fermentation in foods such as homemade soda, wine, yogurt, pickles, bead and sauerkraut (same recipe as kim chee but use only round green cabbage and salt). You can also discuss the beneficial properties of garlic, chili peppers and other spices.

RESOURCES:
Boston University. The Microcosmos Curriculum Guide to Exploring Microbial Space . Iowa: Kendall/Hunt Publishing Company, 1992.

Eddy, Bob. "Kim Chee Collection". {www.cs.cmu.edu/~mjw/recipes/preserves/kim-chee/kim-chee-coll-2.php}

EASC, Indiana University. "Teaching About Korea: Activity Sheet 2". {www.easc.indiana.edu/pages/easc/curriculum/korea/1995/general/actw2.htp}

Hillman, Howard. Kitchen Science. Boston: Houghton Mifflin, 1989.

Ingram, Mrill. Bottle Biology. Iowa: Kendall/Hunt Publishing Company, 1993.


This is one of six lessons in "MIXED-PLATE BIOLOGY, HAWAIIAN STYLE", a collection of biological activities that values the cultures of modern Hawaii's multicultural population. The collection includes:

Hawaii is a land of immigrants. The Hawaiians are believed to have arrived around 1000 AD from the Marquesas Islands in the South Pacific. Starting in the 18th century, Europeans and Americans arrived usually involved in missionary work or seafaring trades. Once agricultural plantations of sugar and pineapple were established in the 20th century, workers arrived from China, Japan, Puerto Rico, Portugal, and the Philippines.

Since the plantation days, immigration has been largely from Southeast Asian nations of Vietnam, Laos, Cambodia, and Thailand; Korea; the South Pacific nations of Samoa and Tonga; the Philippines; as well as the U.S. mainland. As ethnic diversity increases in our classrooms, let's draw from the various cultures to personalize the concepts of biology.

(About the title: a Mixed Plate is a unique lunch that evolved as new immigrant populations arrived in Hawaii and can include pork adobo from the Philippines, teriyaki beef from Japan, kim chee from Korea, bean soup from Portugal, chow mein from China, traditional Hawaiian foods such as lau lau and poi and of course two scoops of rice.)


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