I. Making Sauerkraut (Or Kimchee)

I. Making Sauerkraut (or Kimchee)

Biology

Unit 2: Cells – Structure and Function and Unit 3: Cell Energetics

II. Goal:

a. Big Idea: The concentration of solute in a solution will affect the movement of water across cabbage leaves’ membranes.

b. Purpose: The goal of this lab is to determine the biological changes that occur to the cabbage over a period of time in and to relate these changes to the phenomenon of diffusion and osmosis. The students will also be learning about the pickling process, fermentation, and have the opportunity to taste their results. It gives them a chance to see one way we use our knowledge of science to make tasty (and maybe not so tasty to some) things.

c. HSCE/GLCE Alignment: B2.5h: Explain the role of cell membranes as a highly selective barrier

III. Background:

a. Prior Knowledge:

Osmosis is the movement of fluid through a membrane in order to create an equal concentration of dissolved solids (salt, in this case) in the fluid on either side of the membrane. When you salt a cabbage leaf, you create a difference in salt concentration — higher outside the cabbage leaf and lower inside the cells. In order to equalize the salt concentration, water from inside the cabbage leaf cells will exit through the cell membranes. The water will continue to flow out of the cells until there is an equal concentration of salt in the fluids on either side of the cell wall, or until the cell is completely dehydrated.

The term "FERMENTATION" refers to the activity of bacteria and fungi, such as yeast (which is a single-celled fungus). These microbes break complex compounds, like sugars, into simpler substances, such as carbon dioxide and alcohol. Because these simpler substances are toxic to food-spoiling microbes, they act as natural preservatives for food. Before refrigeration, fermentation was a primary method of food preservation.

b. Reference Sources: Other Great Bottle Ideas can be found at: http://www.bottlebiology.org/index.html

c. Timeframe: 2-3 days for design, procedure, data analysis, and lab write up. Up to two weeks to ferment.

IV. Vocabulary: diffusion, osmosis, aerobic, anaerobic, breakdown of food molecules, tonicity - hypertonic, hypotonic, isotonic (suggested for question at end of lab)

V. Materials: Head of Cabbage (round headed green cabbage), Clean 2-liter bottle, One plastic lid about 9 cm across, Knife, Distilled water, Salt, Electronic balance, pH indicator

VI. Procedure:

(*If you want to have students make kimchee you will need a few extra items: Chopped hot chili pepper or chili powder and Two cloves garlic, thinly sliced. You will layer these with the cabbage and salt. You will also want to use Chinese Cabbage instead of the green cabbage, cut into 4 cm chunks. Otherwise, use the following procedure)

1. Use a sharp knife to cut off the top of your 2-liter bottle. (See picture below to see how to cut the bottle.)

2. Chop the head of cabbage and layer cabbage and a sprinkling of salt (see below to determine total amount needed) into the bottle. Repeat layers until the bottle is packed full, placing the plastic lid on each layer and pressing down vigorously to break up the cabbage and distribute the salt. Make a mark on your bottle where the cabbage layer is. Measure this from the top of the bottle and record it in Table 1. Also measure the pH of your cabbage and record this in Table 1.

How to PREPARE YOUR 2% SALT SOLUTION: People who pickle often use a 2% salt concentration. How much salt must you add to your 2-liter bottle of cabbage to produce a 2% salt concentration?

It just so happens that a 2-liter soda bottle packed full of cabbage leaves weighs approximately 1 kilogram. Cabbage is about 95% water, so you need only to figure out how much salt you need to add to 1 kilogram (1,000 grams) of water in order to create a 2% solution. Two percent of 1,000 (.02 x 1,000) is 20 — you need 20 grams of salt (about 3 tsp).

3. Over the next few hours the teacher will press down the mixture. *Cabbage must be submerged at all times.

4. NOW WE WAIT: Store for several days in the refrigerator (3 days to 2 weeks). Once your pH reaches 3.5, your kimchee or sauerkraut is ready!! Check pH every day or every other day. Record these pHs at the bottom of the lab (indicate date each time). You should see density changes as well. During the first few hours after you fill your sauerkraut bottle, you will observe that the height of cabbage leaves falls by half. The weight of the bottle remains the same, but the density changes. How can you quantify the density changes in your 2-liter bottle?

A 2-liter bottle newly packed full of leaves weighs about a kilogram. Since density is grams per volume (d=g/v), your kimchee or sauerkraut has an initial density of 1 kilogram of cabbage per 2-liter soda bottle, or 1/2. Due to osmosis, however, the cabbage level drops to about half the bottle. In other words, the volume drops to 1 liter. Now the density equals 1 kilogram per 1 liter, or 1. The mass of the bottle hasn't changed, but the density has doubled.

5. Once your pH reaches about 3.5 your sauerkraut is ready. Record this pH in Table 1. Make another mark on the bottle to measure the distance from the top the cabbage has fallen and record it this in Table 1.

6. You can now try your cabbage if you like. Bon Appetite!

Table 1

Original appearance of cabbage / Final appearance of cabbage / Original pH / Final pH / Original volume
(mark on container distance from top in centimeters) / Final volume (mark on container distance from top in centimeters) / Change in pH / Change in volume

QUESTIONS:

1. What was the effect of osmosis on the cabbage cells? Explain why.

2. What was the tonicity of the salt water in which the cabbage was placed?

3. What process caused the cabbage to become “sour” in the kimchee?

4. Was this process anaerobic or anaerobic?

VII. Expected Results:

You might find that it takes the full 2 weeks to make the sauerkraut and you might want to include a table for the students to fill out on the days they are checking the pH. You could also include weighing the bottle on various days to see if there is a change in mass (there should not be one).

What Does Salt Do?
Osmosis and Density Changes in Kimchee (sauerkraut)

BACKGROUND:

OSMOSIS: When you sprinkle salt on cabbage leaves and then exert pressure on them, you'll notice that the leaves become limp and the bottle begins to fill with liquid. Just what is going on here?

Liquid inside the cells of the cabbage leaves is flowing out of the cells in response to the salt, a phenomenon called osmosis.

Genghis Khan's forces 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 in order to prevent scurvy. KIMCHEE is a traditional fermented cabbage dish from Korea. Koreans eat kimchee year round for the spicy taste and because it contains lots of vitamins C and B. You may be more familiar with the traditional German pickled cabbage dish, SAUERKRAUT, a less spicy version of kimchee.

In a bottle fermentation chamber you can pickle your own cabbage. You'll learn a lot about fermentation, and enjoy great-tasting results.

MATERIALS:

· Head of Cabbage (round green cabbage)

· Clean, 2-liter bottle

· One plastic lid about 9 cm across

· Knife

· Distilled water

· Salt

· Electronic balance

· pH indicator

PROCEDURE:

Make sure your hands and work area are clean before starting! As the teacher you may want to do the cutting of the 2-liter bottles yourself (prior to lab). You may also want to chop the cabbage up (or buy it chopped). Up to you. Here is the procedure having the kids do it.

1. Use a sharp knife to cut off the top of your 2-liter bottle. (See picture below to see how to cut the bottle.)

How to PREPARE YOUR 2% SALT SOLUTION: People who pickle often use a 2% salt concentration. How much salt must you add to your 2-liter bottle of cabbage to produce a 2% salt concentration?

It just so happens that a 2-liter soda bottle packed full of cabbage leaves weighs approximately 1 kilogram. Chinese cabbage is about 95% water, so you need only to figure out how much salt you need to add to 1 kilogram (1,000 grams) of water in order to create a 2% solution. Two percent of 1,000 (.02 x 1,000) is 20 — you need 20 grams of salt (about 3 tsp).

3. Over the next few hours the teacher will press down the mixture. *Cabbage must be submerged at all times.

4. NOW WE WAIT: Store for several days in the refrigerator (3 days to 2 weeks). Once your pH reaches 3.5, your kimchee or sauerkraut is ready!! Check pH every day or every other day. Record these pHs at the bottom of the lab (indicate date each time). You should see density changes as well. During the first few hours after you fill your sauerkraut bottle, you will observe that the height of cabbage leaves falls by half. The weight of the bottle remains the same, but the density changes. How can you quantify the density changes in your 2-liter bottle?

6. You can now try your cabbage if you like. Bon Appetite!

Table 1

Original appearance of cabbage / Final appearance of cabbage / Original pH / Final pH / Original volume
(mark on container distance from top in centimeters) / Final volume (mark on container distance from top in centimeters) / Change in pH / Change in volume

QUESTIONS:

5. What was the effect of osmosis on the cabbage cells? Explain why.

6. What was the tonicity of the salt water in which the cabbage was placed?

7. What process caused the cabbage to become “sour” in the kimchee?

8. Was this process anaerobic or anaerobic?