Related Lessons

Food Preservation

In this lesson, students' attention is drawn to the issue of food spoilage and the different methods that are traditionally used to prolong the freshness of food. Using a number of online resources, they learn about how Chilean fruit and lettuce for salad are carefully harvested, treated, packaged, and transported in refrigerated vessels to maintain their freshness. Students are then introduced to the canning, drying, freezing, and vacuum-sealing processes that are commonly used by food producers and in the home.

This lesson has been designed to help students trace the paths that various foods take as they move from growers to consumers. Storage, transportation, preservation, processing, and packaging are considered. Where possible, students should visit markets, farms, grain elevators, and processing plants and examine trucks, trains, cargo planes, and as many other parts of the "technological food chain" as possible. It is important that they know some of the hazards that food encounters from the time it is a seed until it reaches the kitchen. Food preservation and sanitation can be explored in early grades, but explanation of spoilage as the result of microorganisms should wait until 6th through 8th grades. (Benchmarks for Science Literacy, p. 184.)

For many centuries, most food was consumed or marketed within a few dozen miles of where it was grown. Technology has revolutionized agricultural markets through transportation and communication. The many improvements in land productivity have led to availability of far more food in some areas than is needed for the local population. The development of rapid and cheap transportation reduces spoilage of food, as do treatment, additives, refrigeration, and packaging. But rapid, long-distance distribution of farm products also requires rapid, long-distance communication for selling and routing them. Together, modern transportation and communication systems enable food to be marketed and consumed thousands of miles from where it is produced. (Science for All Americans, p. 110.)

It might be helpful for students to realize that only a century ago, a majority of workers in the United States were engaged in farming. Now, because technology has so greatly increased the efficiency of agriculture, only a tiny proportion (about two percent) of the population is directly involved in food production. There are, however, many more people involved in producing agricultural equipment and chemicals, and in the processing, storage, transportation, and distribution of food and fiber. (Science for All Americans, p. 110.)

As noted in the Motivation section, three days before teaching this lesson, it will be necessary for you to cut a peach in half and place one of the halves in plastic wrap in the refrigerator and the other half on a plate left out at room temperature. Make sure the peach that is left out is in a safe place and out of reach of students. The Assessment section includes an optional activity which gives students a chance to compare the taste and freshness of canned and dried fruit. You may wish to consider how to set up tasting stations before beginning the lesson.

Materials:

• Three peaches
• Two tomatoes
• Knife
• Small plates
• Napkins
• Plastic wrap
• Access to refrigeration
• World map
• Can of fruit
• Small glass container of baby food
• Canning jar (or photo if one is unavailable)
• Bag of frozen vegetables
• Frozen entrée box
• Vacuum-sealed food item
• Bag of dried fruit
• Food Preservation student E-Sheet
  Note: In the "Going Online" section of the E-Sheet, students will answer questions using an online tool. As an alternative, students can answer the same questions on the printable Food Preservation student sheet
• Stay Fresh student sheet

Grab your students' attention by taking out a peach, a knife, and a plate. Cut the peach in half and put one half on the plate. Then eat the other half. Tell students that you are full and want to save the other half of the peach for tomorrow. Then ask:

• If I want to eat this peach tomorrow, is there anything I should do with it now? Why or why not?

Once students confirm that it might be wise to wrap the peach in plastic wrap and put it in the refrigerator, ask them:

• What does refrigerating do for the peach?
• What happens when a peach is not refrigerated?
• What might happen if I left it here on this table and ate it in a few days?
  
  (Accept all answers, but ask students to support their views with explanations.)

Students will likely assert that the peach may spoil when left at room temperature. Reinforce that this spoilage may cause illness, so it is a bad idea to leave fresh-cut fruit out for long periods of time. Now take out the peach halves you had prepared earlier. First show students the peach that has been left out for three days at room temperature. Then show them the peach that was refrigerated for three days. Let them compare the appearance and freshness of each. Reinforce that fresh foods spoil and ultimately rot when left out over time, while refrigeration helps to preserve or keep foods fresh for longer periods.

To further reinforce how foods can spoil and ultimately rot when left out over time, tell students that they will engage in a hands-on activity using some fresh fruit.

Take out two tomatoes and place on two plates. Show them to the class and explain that one will be placed into a refrigerator and the other left out in the classroom at room temperature. Students will have the opportunity to observe both pieces of fruit for at least a week to see which one stays fresh longer. This activity will help to further demonstrate the central idea of the benchmark—that different techniques to preserve food, like cooling, can keep food fresher longer than just leaving it out in the open. If possible, have students observe each fruit on a daily basis and discuss any changes in the appearance or edibility of the fruits they are observing. Students should use the Stay Fresh student sheet to record their observations by writing down an explanation of what they see and by drawing pictures of what the tomatoes look like.

Then, to help students think about storage and preservation on a more global level, ask these questions:

• Where do you think the peaches and tomatoes we have used in this lesson came from?
• Is all fruit grown in the U.S. or do we sometimes import it from other countries?
• Why do you think fruit from other countries doesn't spoil when it is shipped to our supermarkets?
  
  (Accept all answers, but ask students to support their views with explanations.)

Using their Food Preservation student E-Sheets, have the class visit the following resources to learn about Chilean fruits. It's best for students to read these resources in order:

• What Fruit Grows in Chile?
• How Are Chilean Fruits Harvested and Packaged?
• How Are Chilean Fruits Transported to the United States?

The following questions are found on the student E-Sheet. Students can either respond to the questions online, using the online question and answer tool, or they can use the printable Food Preservation student sheet:

• What kinds of fruits and vegetables does Chile send to the U.S.?
• What percent of all peaches in the U.S. come from Chile?
• What happens to the fruit once it is harvested?
• Why is the fruit packed into specially designed boxes?
• What forms of transportation are used to send the fruit to the U.S.?
• How is the fruit stored during these trips?
• How long does it take for fruit to be shipped from Chile to the U.S.?
• What might happen if the fruit was not refrigerated?

During this discussion, emphasize that cooling fruit slows the spoilage process and keeps it fresh. That is why people use refrigerators at processing plants, on ships and planes, at supermarkets, and in our homes. Inform the class that cooling is only one way to help preserve food and that they will now learn about other methods.

To get the class thinking about other ways we preserve food, ask these questions:

• Besides fruit, what are some other foods that need to be specially handled to avoid spoiling?
• What are some of the ways these foods are specially handled?

To highlight some of these other approaches, have students use their student E-Sheets to Tour a Fresh-Cut Salad Factory, on the Dole 5 A Day site, which describes the process for harvesting lettuce, preparing it into fresh-cut salad, and getting it to market.

Like the Chilean fruit, this lettuce is harvested and kept cool in state-of-the-art plants. To be transformed into fresh-cut salad, however, it is triple-washed, cut with a “megacutter,” and spun dry with special machines before being sealed into packages to maximize freshness.

In addition to the general review questions about the plant, ask benchmark-supporting questions such as these:

• What is done to help keep salads fresh during the packaging process?
• Why is a wash system used?
• Why are centrifugal dryers important in the packaging process?
• What is the most important step in the salad-making process? Explain.
• What keeps packaged salads fresh during their journey from the plant to grocery stores?
• Where in the grocery store do you find packaged salads?
• What might happen to the salad if it was not treated this way?
• What are the benefits of buying fresh-cut salads?

Next, inform the class that, in addition to these approaches to cooling, drying, and packaging foods, there are a number of other techniques that people use to slow spoilage and keep foods. Display the following items: a can of food, a small glass container of baby food, a canning jar, a bag of frozen vegetables, a frozen entrée box, a vacuum-sealed food item, and a bag of dried fruit. Put each of these items in one of four groups: canned, frozen, vacuum-sealed, and dried. Ask students what they can tell you about each group of items. Accept all reasonable answers. Encourage them to talk about how these types of preserving and packaging help food last longer and make our lives easier. Also inquire if any of their relatives ever can, freeze, vacuum-seal, or dry foods at home.

After this brief discussion, have students visit How Food is Canned to get a simple, illustrated picture of how food producers in Australia can vegetables and fish. Have students follow the arrows in each process carefully.

Note: You may need to explain the line, "produce is harvested at its optimum maturity and nutritive value" from the opening section. You may also need to explain that cooking or sterilizing the cans kills germs (microorganisms) that can cause the food to spoil. (Do not go further in explaining what causes spoilage.) The bottom section on can labeling should be overlooked. During this exploration of canning, ask questions like these:

• How is the canning of pears and fish similar? Different?
• Why is sealing important?
• Why do you think fish is frozen after it is caught?
• Do you have any canned fruit or fish at home? How do they taste? How long do they last compared to fresh fruit or fresh fish?

Review with students what they have learned about the techniques used to slow the process of spoiling and extend the freshness of food. Emphasize the science, technology, and special transportation and storage necessary to preserve food.

To further extend students' understanding, you may ask them to respond to questions such as these:

• What would our lives be like if we didn't preserve food?
• Were you surprised to learn about all the different steps needed to preserve food? Why or why not?
• Which do you like better—canned or frozen vegetables? Why?
• Why is it a good idea to try to preserve food at home?
• What are some good habits to have at home when you are handling fresh food or leftovers?
  
  (Accept all answers, but ask students to support their views with explanations.)

Optional Activity—Snack N’ Chat
As a treat and extension of the review, you can set up a tasting station where students can comprare the taste and freshness of the canned and dried fruit that were used as props earlier in the lesson.

The Science NetLinks lesson Global Breakfast allows students to further explore the origin of the food they eat, in the context of global interdependence.

For further reinforcement on the food-to-table process, students can visit Wheat: From the Farm to You, an exhibit on the 4-H Virtual Farm. This exhibit takes students to a wheat farm to observe how crops grow, how they're processed, and the extensive, high-tech journey they take before becoming the products we buy in supermarkets. Encourage the class to explore the other virtual farms on the site, including horses, fish, dairy, beef, and poultry.

More advanced students at the higher grade levels who want to learn more about the science of spoilage can visit How Food Preservation Works. This resource provides a more in-depth explanation of food preservation and the various methods used over time.

Created :04/05/2004