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Sun-dried Foods

This is a classroom activity on food dehydration that demonstrates the concepts of food preservation and of atmospheric humidity. Students predict which types of food contain the highest percentage of water, then air-dry their foods in the classroom. Daily weighing of the foods encourages students to test their earlier predictions. Groups of students record and discuss their daily observations. A narrative about Native American preparation of sun-dried foods illustrates the importance of food dehydration.

Key Concepts

Atmospheric Science, Humidity, Dehydrating Foods

Program/Collection

Multicultural Classroom Activities  View All »

Duration

2 - 50 minute class periods

Audience

K-2, 3-5

Partners

National Teachers Enhancement Network

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http://btc.montana.edu/courses/aspx/lessons.aspx?TheID=32

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Topics

Life Science

Resource Type

Extended Lesson Plan

Format

Website

Updated

10/25/2013

You'll find additional information specific to this extended lesson plan below.

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More Info for this Extended Lesson Plan

Background

For the native tribes of North America, gathering food to prepare for the long winter months was a main focus of both men and women. The Blackfeet Indians of present-day Montana and Alberta used food preparation methods common to many Plains Indians. In the warm summer months, they gathered roots for medicine, teas, soups and other mainstays, as well as berries and meat to eat. Food had to be preserved to use later during winter weather when hunting and gathering were not always possible. Different types of food were dried, or dehydrated. For example, the Blackfeet would smash berries using rocks to form a mash. The berry juice was used to dye clothing and for decoration, but the mash was spread out on an animal hide and put in the sun to dry. Animal fat was cut into small strips and dried, then mashed together with berries to form pemmican cakes, which did not need refrigeration to keep from spoiling. Leaves, roots, and other edible plant parts also were spread in the sun to dry, then stored to use later in medicinal teas and salves. Meat often was cut into extremely thin slices and hung on racks made from branches to dry naturally in the sun, forming a jerky that would last throughout the winter. Other tribes ground dried corn into a powder for use in soups.

Dehydrating foods is one of the oldest known methods of preservation. All of the water content must be removed from the food in order to keep bacteria and mold from growing and spoiling the food. The "sun-dried" method was the traditional dehydration technique used by Native Americans. In order for food to dry properly, the day must have low humidity, lots of sunshine, and sufficient air circulation. Drying should be done as quickly as possible at a temperature that does not seriously affect the texture, color and flavor of the vegetable or fruit. Water from the inside of the food moves to the surface and evaporates, so food must be cut into thin slices to speed the process of water evaporation. As the water evaporates, the food loses weight and develops a skin on the surface. If the temperature is too high and humidity too low, there is danger that moisture will be removed from the surface of the food more rapidly than water can diffuse from the interior and a hard crust will form on the food. This thicker layer will not permit free diffusion of moisture from the inside and the product will not dry properly. Sun drying can take up to a week or 10 days, depending on the food being dried, the air temperature, and the amount of atmospheric moisture or humidity.

Understanding the role of humidity is critical for successful solar dehydration. Humidity is the amount of water vapor in the surrounding air. Humidity is measured as a percentage of the amount of water vapor in the air compared to the amount of water vapor that the air can hold at that temperature. When the humidity is 100 percent, fog or clouds form in the air. Air temperature affects how much water vapor can be present before clouds form. For example, at warmer temperatures, more moisture can be present before fog or clouds begin to appear.

Humidity is measured by a hygrometer. The wet bulb hygrometer uses a thermometer wrapped in a wet wick to measure the wet bulb temperature. Evaporation takes up heat, the thermometer will cool to a lower temperature than a thermometer with a dry bulb at the same time and place. The humidity can be calculated from the two temperatures, or read from tables or a chart like the one below. (Find the point where the blue lines from the wet bulb temperature axis cross the red lines from the dry bulb temperature axis. Then follow the green curves to read off relative humidity, or the black, horizontal lines to read the absolute humidity.)

Problem/Purpose

The purpose of this activity is to give students an introductory understanding of atmospheric humidity. Students dehydrate different types of food using ambient classroom air and temperatures. After predicting which food types contain the most water, students weigh their foods daily and record the results. They also learn that Native Americans traditionally prepared sun-dried foods to eat during the long winter months.

Author

Theresa Murray
Cultural Consultant - Prarie Band Potawatomi

My name is Theresa Murray. I am a Prairie Band Potowatomi Indian from Topeka, Kansas. I am married to Rober D. Murray Jr., an Assiniboine/Sioux Indian. We live in Poplar, MT. the tribal headquarters of the Fort Peck Reservation. We have three children: Isaac a sophomore who is currently attending Fort Peck Community College in Poplar; Jessie, who just graduated high school in Poplar and will be attending college in Missoula this fall; and Bobby, Robert Murray III is a freshman at Poplar High School. I have taught the 5th and 6th grades in Poplar Middle School for the past five years. Before that I worked at For Peck Community College as a Distance Learning Assistant for three years while I was completing my college education. I worked as City Clerk for the City of Poplar for 9 years until I returned to college and started to work as a Tutor under the CSAP program (Center for Substance Abuse and Prevention Program) for 3 1/2 years then I transferred to the high school and worked 1 year there. I worked full time and attended college full to part time while raising my three children. I am currently completing a Technology in the Classroom Master's Program through Lesley College, Cambridge, Massachusetts. I will complete it in the spring of 2004. I am serving my second term on Poplar's City Council.

Vocabulary

Learner Outcomes

  • Discuss the relative moisture contents in various types of food.
  • Dehydrate foods in the classroom, testing their predictions of which foods contain the higher percentage of water.
  • Understand the concept of atmospheric humidity and why it is important.
  • Appreciate that native communities used dehydration to preserve food to eat later during the winter when fresh food was less plentiful.

Content Standards

  • Blah

Materials

  • Clean window screens
  • Spoons (one/group of 4 students)
  • Large cotton dish towels or white cloth
  • Clothes pins
  • Small roast beef, Head of lettuce, Tomatoes, Strawberries, Apples, Stalks of Celery, Ears of corn (or bag of frozen corn kernels)
  • 11” x 14” poster paper (one/group of 4 students)
  • Pencils, pens, markers, crayons
  • Sharp knife for teacher use
  • Scale to weigh food pieces

Lesson Procedures

  • Gather students into a large group. Discuss how Native Americans used dehydration to prepare foods for the winter. Make a list of dehydrated foods that we eat today. Discuss how dehydration works and the importance of humdity.
  • Show students the various vegetables and meat. You can substitute any fruit or vegetable that is in season. It works best if they can be thinly sliced. Ask students which food they think contains the most water. Have students write a list of the foods in order of expected water content -- for example, from highest moisture content to least.
  • Divide class into groups of 3-4 students. Give each group a sheet of 11 x 14 poster paper. Tell students that each group is going to be in charge of dehydrating a food. Assign a food to each group, but don't distribute the foods yet. Have each group write the name of its assigned food at the top of the group paper. Have them make a grid on the rest of the paper (see below). The first column should be labeled Date, the middle column should be labeled Weight and the final column should be labeled Drawing. Tell the class that each group must weigh its food every day, record the date and weight, and draw the food on the sheet of paper.
  • Give one food to each group (teacher will go from group to group and slice the food into smaller pieces for better dehydration). Students with whole corn cobs will use a spoon to remove the kernels.
  • Have each group go to the scale and weigh their food. Record it on data sheet. Each group also will record the date and draw the food on the sheet.
  • Instruct each group to place a dish towel on top of a window screen. Have students place their food on the towel with no pieces touching. Cover with another towel and fasten with clothes pins. Multiple groups can place their food on a single screen. Place the screens in the same location in the classroom.
  • Have each group weigh food daily. Make certain they don't touch other groups of foods.
  • At the end of a week, meet in a large group and compare data sheets. Have students subtract the final weight from the initial weight. This is the total weight lost. Which food had the most amount of water lost? Why? How did this compare to their initial guess? What would happen if they let the foods dehydrate longer?
  • Have students go back to their seats and write an individual journal on why they think some foods lost more water than others.

Conclusions

  • Different types of foods contain different amounts of water.
  • Dehydrating foods is one way to preserve food without refrigerating or freezing.

Assessments

  • Participation in class discussions
  • Participation in group data sheet
  • Individual journals

Extensions

  • Visit your local grocery store and identify different foods that have been dehydrated.
  • What other methods are used to preserve food for long periods of time?
  • Use the Internet or other resources to learn more about humidity in the atmosphere and why it is important. Do you live in an area with high or low humidity?

Resources