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Science and Our Food Supply - Middle School Guide: Module 4 - Retail and Home

Science and Our Food SupplyTeacher's Guide for
Middle Level Science Classrooms

2007 Edition

Return to Table of Contents

MODULE 4 - RETAIL AND HOME

ABOUT THE MODULE

Examines the preparation of food in retail food-service establishments and in the home.

Hand holding a pencil in a green circle background Supermarket Smarts - explores all the aspects of safe food handling in a supermarket.
Empty flask and half-filled test tube in a green circle as background The Science of Cooking a Hamburger: Cooking Right - shows the relationship between the temperature to which a hamburger is cooked and the presence of bacteria.
Empty flask and half-filled test tube in a green circle as background A Chilling Investigation - investigates the effect of chilling and not chilling on the growth of bacteria.
Empty flask and half-filled test tube in a green circle as background Crossed Up! - examines how bacteria can be spread among the items in a kitchen if they are not properly cleaned.
Empty flask and half-filled test tube in a green circle as background Hands Off, Bacteria! - analyzes handwashing and its connection to food safety.

 

SCIENCE CONTENT

Video tape in a green circle backgroundThis section explains the specific science concepts presented in Module 4 of the video/DVD, including fascinating facts relative to the module. Read this section before watching the video module or conducting the activities and experiments.

RETAIL

The 4 Cs Connection - In any restaurant or place that serves food, the 4 Cs are critical. Sometimes, the 4 Cs can be taken care of by technology.

Hi-Tech Hamburgers - Fast-Food Technology

A man and woman standing over a two-sided grill
Two-sided grill

To eliminate human error, an engineer developed a 2-sided "clam shell" type grill that has a temperature sensor. It cooks burgers on both sides simultaneously, using a sensor to assure that all of the burgers reach a safe internal temperature.

Important Note: The "clam shell grill" is only one way to ensure safer food. Other methods, such as cooking on a grill and flipping burgers, are also effective. The point is to assure that foods are cooked to a high enough temperature to kill any pathogens.

Handwashing

Humans are one of the biggest sources of food contamination in restaurants. So, handwashing is critical to keep food safe. For example, contamination can occur when someone doesn't wash their hands and then prepares or serves food.

FASCINATING FACTS

50 billion meals a year are eaten outside the home.

Supermarkets

A woman with a child in the cart of a grocery store aisle
The milk is stored in clean,
temperature-controlled
display cases.

Receiving areas are maintained at cold temperatures of 41° F (5° C) or below to maintain the cold chain that started way back in the field.

Storage areas and display cases are kept clean and temperature controlled.

Food preparation areas are also kept clean, and are set up to avoid cross-contamination.

Foods are always separated to avoid cross-contamination. Red meats, fish, and poultry will never be mixed together or mixed with fruits and vegetables.

HOME

Even with all the great technology, food can still become contaminated, so it's important for YOU to always practice the 4 Cs of Food Safety. Once you purchase food and take it home, the responsibility for food safety is literally in your hands.

woman serving family at a dinner table
The Barkley family
practicing the 4 Cs
of Food Safety.

Overview of 4 Cs in the Home

Clean - Wash hands and surfaces often. Wash hands with warm, soapy water, and cutting boards, dishes, utensils, and surfaces with hot, soapy water before and after food preparation.

Cook - Cook foods to proper temperatures. Using a food thermometer is the only reliable way to ensure that hamburgers, meat, and poultry reach a safe internal temperature.

Combat Cross-Contamination - Keep raw meats, poultry, and seafood - and the juices from raw foods - away from other foods in your shopping cart, on kitchen counters, and in your refrigerator.

Chill - Refrigerate promptly. Refrigerate or freeze foods quickly because cold temperatures keep harmful bacteria from growing and multiplying. The 2-Hour Rule: Refrigerate or freeze perishables, prepared foods, and leftovers within 2 hours or less.

 

Hand holding a pencil in a green circle background

SUPERMARKET SMARTS

Time: Two 45-minute class periods - one for an introduction to the activity and one for the presentations

ACTIVITY AT A GLANCE

In this activity, students will develop an awareness of the importance of food safety in retail food establishments. They will be challenged to design and manage their own food-safe supermarket department, from researching the food-safety needs of a specific food department through designing that department using the 4 Cs of Food Safety. At the end of this activity, each team will present its findings in an innovative presentation. (A fast- food restaurant could be substituted for a supermarket. See the Fast Food Footwork activity of the High School Teacher's Guide.)

FOOD SAFETY Plate, Knife and Fork CONNECTION

Students purchase food from retail establishments. Exploring all the aspects of safe food handling in a supermarket (or fast- food restaurant) will help make them better consumers and employees.

 

GETTING STARTED

MATERIALS

ADVANCE PREPARATION

  • Write the names of each supermarket department on a separate piece of paper. (These departments offer a good variety of food-safety principles.)
    - Meat/Poultry/Seafood
    - Deli
    - Produce
    - Dairy/Eggs
    - Checkout/Employee break area
  • Place the papers in a grocery bag, and place the bag on your desk.

 

INTRODUCTION

I have a challenge for you! Today we're going to take on the role of managing specific departments in a supermarket. But before we begin, let's find out what Dr. X and Tracy say about food safety at the supermarket and in restaurants. 

Video tape in a green circle background TIME TO TUNE IN . . . Module 4 - Retail and Home

PART 1 - RETAIL

Here are some questions to think about while you're watching the video:

  • How do supermarkets practice the 4 Cs?
  • How are supermarkets a link in the cold chain?
  • What does Dr. X mean when he says, "The responsibility for food safety is literally in your hands"?

Show video/DVD Module 4, Part 1 - Retail (Time: 3 minutes).

Video tape in a green circle background INSTANT REPLAY  Time to review and summarize.

1. Dr. X told us that supermarkets are "major 4 C territory." What did he mean by that?
(Clean - Employees in restaurants and food stores must clean their hands. Storage areas and display cases must be kept clean.
Cross-Contamination - Food-preparation areas must be kept clean to avoid cross-contamination. There are separate departments for raw meat, fish, poultry, and produce to avoid cross-contamination.
Cook - Temperature probes should be used to make sure that food is cooked to the right temperature.
Chill - Foods need to be chilled or frozen to stay fresh.)
2. Dr. X discussed the "cold chain." What is it? (The cold chain is a series of actions that maintain the temperature of food as it travels from the farm to the table.) How does the cold chain come into play in the supermarket? (Supermarkets are a link in the cold chain. Storage areas and display cases are kept at a safe temperature to keep food frozen or chilled.)
3. What does Dr. X mean when he says, "The responsibility for food safety is literally in your hands"? (Handwashing is critical to keeping food safe. Contamination can occur when someone doesn't wash his/her hands and then prepares or serves food. Employees must follow strict handwashing guidelines, and customers should wash their hands before they eat the food.)

PROCEDURE

1.Divide the class into 5 teams.
2. Have a member from each team select a department from the grocery bag. Tell the teams: Today, you'll be the manager of your supermarket department. Your challenge is to reduce the opportunity for foodborne pathogens to grow or spread. Work with your teammates to create a food-safety program for your department.
3. Have each team develop a plan for assuring that the food in their department is safe, and prepare an innovative presentation to present their plan. Students can consider the following actions:

  • Research the food-safety needs of the department by using the Internet and/or interviewing a store manager.
  • Research local, state, and federal regulations to find out what procedures the store personnel must follow.

4. Design the department so that it follows the 4 Cs of Food Safety.

  • Analyze the role that the 4 Cs of Food Safety play in the department.
  • How does the cold chain come into play in the department?
  • Include handwashing recommendations for the employees.

5. Present the department design to the class, and show how food safety was incorporated into the department. Make a Power Point presentation, Web page, poster, advertisement, poem, song, play, or 3-D model. Or come up with an original idea.
6. Have the class compare the food-safety needs found in each of the five departments. Ask students: What are the similarities and differences?

Video tape in a green circle background INSTANT REPLAY  Time to review and summarize.

1. What are some things you discovered about supermarket food safety that you didn't know?
2. What do you think science has to do with supermarket food safety?
3. What's one of the most important things an employee can do to prevent foodborne illness? (Wash his/her hands.)
4. Whose responsibility is it to keep food safe once the food is purchased? (The customers)

RESOURCES

T I P S

For more activities related to Retail, see the High School Teacher's Guide activity, Fast Food Footwork, in Module 4.

SUMMARY

Food safety is an important aspect of designing and managing a supermarket. There are strict regulations governing food service, and the regulations are science-based. Everyone has responsibility for food safety - managers, employees, and customers.

EXTENSIONS

Supermarkets

  • Interview a local supermarket manager and find out how he or she assures food-safety.
  • Create an FBI Case scenario about what happens to the food between the time you take it out of the supermarket and get it home. Build in at least three 4 C violations. You can also try to identify the violations and then propose a plan for minimizing the risk.
  • Trace a food through the supermarket. How is it kept safe until you purchase it? How many times is it touched and by whom? Is there a way to ensure that all those who touch the food have clean hands? Report your findings.

Other Food-Service Establishments

  • Ask your school's food-service manager to speak to your class about the food-safety guidelines they follow. How do those guidelines relate to the 4 Cs of Food Safety?
  • Do a follow-up lesson applying what you've learned in this activity to restaurants, picnics, cookouts, banquets, and your own kitchen at home.
  • Plan a food-safety training session for employees in your area of the supermarket. Make a list of guidelines that each employee must follow. Present to the class.

Food-Safety Portfolio

  • Use your food-safety portfolio to record how your foodborne pathogen relates to your findings in this activity.

 

Career Connection icon with lab coat (large)

See real-life scientists in action!

  • Food Safety A to Z Reference Guide

 

UP NEXT

Now that you have managed your own supermarket department, let's see how well you do in the kitchen. Find out what's cooking in the next lab activity!

 

Empty flask and half-filled test tube in a green circle as background (large)

THE SCIENCE OF COOKING A HAMBURGER: Cooking Right

Time: One 45-minute class period to conduct the experiment. Observe results at the beginning of the next class period.

LAB AT A GLANCE

The teacher will demonstrate cooking hamburgers to different temperatures. Students will analyze Petri dishes inoculated with hamburger and observe the amount of bacteria at each temperature. They will also learn that cooking hamburgers to the recommended temperature of 160° F (71° C) will kill pathogenic bacteria. Hamburger is used for this cooking experiment because it's a food that students are familiar with and may be cooking at home.

FOOD SAFETY Plate, Knife and Fork CONNECTION

Hamburgers are a staple in the diet of many teenagers. Knowing how to cook them to a safe internal temperature is important to prevent foodborne illness.

 

GETTING STARTED

MATERIALS

For Cleaning and Disinfecting

  • Dishwashing detergent
  • Disinfecting bleach solution (20 ml of liquid household bleach in 1 L of tap water, see Laboratory Procedures)
  • Alcohol wipes or cotton balls and isopropyl alcohol
  • Paper towels

For Preparing and Cooking Hamburger

  • .5 pound (227 grams) of inexpensive, raw hamburger, such as chuck (4 patties, approximately 50 grams each - do not use pre-molded hamburgers)
  • Metric ruler
  • Scale for weighing the hamburgers
  • Hot plate and a regular skillet
  • Non-stick spray to keep the hamburgers from sticking to the pan during cooking
  • 1 digital, instant-read food thermometer (rapid-read, thin-probe type is best)
  • Sharp knife
  • Spatula for removing hamburgers from skillet
  • Clean paper plates for cooked hamburgers

For Swabbing Petri Dishes

  • 5 sterile Petri dishes with nutrient agar and covers
  • Parafilm or masking tape to seal dishes
  • Sterile, cotton swabs
  • Permanent marker

For Safety

  • Thermal gloves or hot pads for handling the hot skillet
  • Safety gloves, safety glasses, lab aprons for anyone handling and/or cooking meat

ADVANCE PREPARATION

  • Review Demonstration Lab Sheet: Cooking Right to prepare for class demonstration.
  • Purchase hamburger.
  • Prepare 5 sterile Petri dishes containing nutrient agar.
  • Familiarize yourself with the proper use of a food thermometer.
  • Review Background.
  • Photocopy Demonstration Lab Sheet: Cooking Right for each student (optional).
  • Prepare 1 hamburger patty (approximately 50 grams) to cook as students enter the class room.

Note: This experiment is designed as a teacher demonstration. If you prefer, and your school allows students to handle and cook raw meat in the lab, you can have students conduct the experiment. (See the High School Teacher's Guide.)

T I P S

  • Take the hamburger out of the refrigerator about a half hour before class, just long enough to warm it up a bit. This will speed up the cooking process.
  • In warmer weather you might conduct this experiment outside on a grill instead of inside using a hot plate.

 

INTRODUCTION

Have a hamburger cooking as students walk into the room. Ask students:

  • How do you want your hamburger cooked - well done, medium, or rare? Take a tally of the class. Now ask, Why? Let them discuss their reasons for about 5 minutes.
  • If no one has brought up, "it's safe to eat or so you won't get sick," ask: How can you be sure that this hamburger will be safe to eat? List the students' answers. Then explain: Today you're going to use science to help answer that question. What do you think science has to do with cooking a hamburger? Let's find out!
  • Explain to the students that most hamburger from the supermarket is safe, however there is a remote possibility that bad bacteria, such as E. coli O157:H7, can find its way into some foods, like hamburger. Because there's a possibility that E. coli O157:H7 can be in our hamburger, it's important to cook all ground meat to a safe internal temperature.
  • We're going to explore the amount of bacteria present in raw hamburger and in hamburgers cooked to different temperatures. Let's see what happens!

SAFETYFIRST

 

  • DO NOT EAT OR TASTE ANY OF THE HAMBURGER used in the experiments.
  • Your hands and lab surfaces may be contaminated after being in contact with raw meat.
    - Disinfect any surfaces that come in contact with the raw meat (see Laboratory Procedures.)
    - Thoroughly wash your hands before and after handling the raw meat.
  • Wear safety gloves, safety glasses, and lab aprons when handling or cooking the meat.
  • Beware of hot surfaces. Use a thermal hot pad when handling skillets, hot plates, etc.
  • Thoroughly wash all thermometers between uses with soap and water, or clean with alcohol pads.
  • Properly dispose of all raw meat.
  • Seal all dishes with Parafilm or masking tape. Never open a Petri dish with organisms in it; some organisms could be dangerous pathogens.

BACKGROUND

  • It's particularly important to thoroughly cook ground meats, such as hamburger, because there's a greater chance for bacterial contamination with ground meat than with whole cuts. The bacteria start out on the outside of the meat. When the meat is ground, any bacteria on the outside can be distributed throughout the hamburger. In addition, when making patties, harmful bacteria from hands, utensils, and surfaces can be transferred inside the hamburger patty. It's important, therefore, to make sure that the internal temperature of the hamburger has reached a high enough temperature (160° F [71° C]) to kill any foodborne pathogens.
  • An "instant-read" dial food thermometer with a probe in the tip is best for checking the proper temperature of hamburgers. The probe should be inserted in the side of the burger, so the entire sensing area (usually 2 to 3 inches [5 to 8 cm]) is positioned into the center of the burger.
  • It may not always be possible to check the hamburger with a thermometer, for example, when you're eating in a restaurant. In this case, the safest thing is to ask for the hamburger to be cooked to a temperature of 160° F. Send it back if it's pink in the middle.

FASCINATING FACTS

  • Research done by the U.S. Department of Agriculture shows that 1 out of every 4 hamburgers turns brown in the middle before it is safely cooked. Some ground beef patties look done at internal temperatures as low as 135° F (57° C).
  • Less than half the population owns a food thermometer. And only 3% use a thermometer when cooking foods like hamburgers at home.

PROCEDURE

LAB 1 Teacher Demonstration with Guided Inquiry

 

Use the Demonstration Lab Sheet: Cooking Right as a guide for conducting the experiment. Use the following suggestions for guided inquiry to help students analyze and design the experiment as you demonstrate.

1. Ask volunteers to assist you in labeling 5 Petri dishes: control, raw, 120° F (49° C), 140° F (60° C), 160° F (71° C); see Laboratory Procedures.
2. Demonstrate how to set up a control dish.
3. Show students how to swab the raw hamburger, inoculate the "raw" dish, and tape the dish to seal (see Laboratory Procedures).
4. Ask students:

  • What factors should be considered as we conduct this experiment? (Weight, size, thickness of hamburgers, temperature, consistency, etc.)
  • How can we assure that all the hamburgers are the same size? (They should be weighed.) Why? (If the hamburgers vary in size, another variable is introduced.)
  • Does thickness of the hamburgers matter? (Burgers should be about .5 inches [1.3 cm] thick. It's easier to accurately insert the thermometer in a burger of this thickness.)

5. Demonstrate how to prepare 3 hamburgers
- weigh and measure them to assure that they are all the same weight and thickness. Option: Have student volunteers make, weigh, and measure the hamburgers. Make sure students wear safety gloves and follow safety procedures for handling raw meat (see Safety First in the Laboratory).

6. Cook one hamburger to 120° F (49° C).

  • Ask students: Why is it important to take the hamburger out of the pan to measure the temperature? (The heat from the pan will interfere with getting an accurate temperature reading of the inside of the hamburger.)
  • How should you take the temperature? (Take the temperature through the side and into the center, making sure the temperature probe reaches the center of the burger, not just the outer edge. Follow the instructions on the thermometer package.)
  • Clean the thermometer with alcohol each time you take the temperature. Ask: Why is this necessary? (If there are bacteria in the meat, they might get onto the thermometer and be transferred to the next hamburger you're cooking.) What is this called? (cross-contamination) Note: We're using alcohol to kill any bacteria and prevent cross-contamination in this experiment. However, when you're cooking at home, you can thoroughly wash the thermometer with soap and hot water between uses.

7. When the hamburger has reached 120° F (49° C), break it in half and demonstrate how to swab the inside. Ask: Why do you break it rather than cut it in this scientific test? (The knife might have bacteria on it and you might transfer that bacteria into the hamburger.)
8. Have a volunteer swab inside the broken edge of the hamburger and inoculate the "120° F" dish. Tape the dish to seal.
9. Cook the remaining hamburgers to 140° F (60° C) and 160° F (71° C), have volunteers inoculate the dishes after each hamburger has reached the desired temperature. Tape dishes to seal.
10. Place the inoculated Petri dishes in the incubator at 35° C (95° F) for 1 to 2 days.

LAB 2 Observe, Record, and Report

 

At the beginning of the next day's lab, have students observe, record, and report bacterial numbers in the 4 samples. Ask students to discuss:

  • Which temperature produced the most effective results in reducing bacterial numbers? (The temperature of 160° F [71° C] should show the best results. This is the recommended temperature for safely cooking ground meat.)
  • How did the amount of bacteria in the raw hamburger compare to the cooked burgers? (The raw hamburger will have much more bacteria than any of the cooked hamburgers.)
  • What did your control show?

INSTANT REPLAY Time to review and summarize.

1. What are some things we've learned in this lab? Here are some probable student responses, but probe for more: - Cooking a hamburger to 160° F (71° C) is the only way to tell that a hamburger is safe to eat.
- Temperature should be taken in the center of the hamburger from the side.
- Surfaces used to prepare raw meat must be thoroughly cleaned before preparing other foods on them.
2. What are some ways our food can become contaminated after we purchase it? (List students' responses.)
3. Does what we learned about hamburger apply to other foods as well? What about poultry? Fish? Seafood? Eggs? (The general learnings about cooking apply to raw poultry, fish, seafood, and eggs.) For proper cooking temperatures and other information about poultry, fish, seafood, and eggs, see the 4 Cs section of the Food Safety A to Z Reference Guide and the Safe Food Chart.

RESOURCES

SUMMARY

It's important to cook meat to a safe internal temperature. The best way to determine if meat is cooked correctly is to use a food thermometer. Hands and surfaces must be thoroughly cleaned before and after coming into contact with raw meat.

EXTENSIONS

  • Trace the path of a hamburger from the farm to the table. What does everyone along the continuum do to help assure that the hamburger is free from E. coli O157:H7 when it reaches you? Complete the continuum by indicating where your responsibility begins and what you must do to ensure that the burger is safe when you eat it. Include each of the 4 Cs of Food Safety in your report.
  • Write a brochure on the importance of food- safety precautions to be distributed to the school administrators and groups cooking at sports events, school events, fundraisers, etc.
  • Visit a local fast-food restaurant and interview the manager to find out how he/she makes sure the hamburgers are cooked to a safe internal temperature.
  • Prepare a food-safety campaign on using a food thermometer when cooking meat for your local PTO or other parent organization.
  • Relate your pathogen to this experiment and record the information in your food-safety portfolio.
Career Connection icon with lab coat (large)

See real-life scientists in action!

  • Food Safety A to Z Reference Guide

 

UP NEXT
Wait until you see how cool the next lab activity will be, literally! We're going to investigate what happens when we don't refrigerate hamburger. A "Chilling" Investigation is up next!

 

DEMONSTRATION LAB SHEET

COOKING RIGHT

GETTING READY

  • Wash your hands with hot, soapy water.
  • Use one alcohol wipe to sanitize the outside wrap of the hamburger, and one alcohol wipe to sanitize the knife.
  • Carefully remove the wrap from the hamburger by slitting the wrap along 3 sides of the package, being careful not to touch the meat with the knife. Then peel the wrap away from the meat. This helps ensure that you haven't cross-contaminated the hamburger with the knife or the wrap. This is important for a scientific experiment, but not necessary at home.

CONDUCT THE EXPERIMENT

1. Prepare a control plate.
2. Remove a small section of the raw hamburger and swab inside the hamburger to get the juices. Inoculate the "raw" plate. Discard the raw hamburger section.
3. Divide the remaining hamburger into thirds. Weigh them to ensure equal weight (50 grams is a good size for testing). Make 3 patties each .5 inch (1.3 cm) thick.
4. Spray the skillet with non-stick spray to keep burgers from sticking.
5. Cook one hamburger to 120° F (49° C). Don't push down with the spatula - it squeezes the juices out.
6. Lift the patty out of the pan with a spatula and place it on a clean paper plate to take the temperature. Temperature should be taken within 15 seconds to get an accurate reading, because the hamburger continues to cook even though it's removed from the heat source.

  • Take the temperature by inserting the thermometer through the side into the center of the burger.
    - One person should use a spatula to steady the hamburger on one side while another person quickly takes the temperature. Remember that the hamburger is hot!
    - If the temperature hasn't reached 120° F (49° C), return the burger to the skillet and continue to cook.
    - If the temperature is higher than 120° F (49° C), return the burger to the skillet and continue to cook to 140° F (60° C). You will then use your third patty to cook to 120° F (49° C).
  • Clean the thermometer with an alcohol wipe each time you use it. Remember that bacteria are not killed until the burger reaches the correct temperature. If the burger hasn't reached the correct temperature, you might reintroduce bacteria into your burger with a contaminated thermometer.

7. Break the patty in half and place on a paper plate. Swab inside the broken edge to get the juices from the burger. Inoculate plate 120° F (49° C).
8. Repeat this procedure, cooking patties to 140° F (60° C) and 160° F (71° C).

INCUBATE PETRI DISHES

1. Tape the dishes to seal (see Laboratory Procedures).
2. Place Petri dishes in an incubator at 90° F (32° C) or let the dishes sit at room temperature (away from the sun) for the appropriate amount of time.

Observe, record, and graph bacterial growth of the samples.

 

Empty flask and half-filled test tube in a green circle as background (large)

A CHILLING INVESTIGATION

Time: One 45-minute class period to conduct the experiment Observe and record the results the next day

LAB AT A GLANCE

Students will observe the difference in bacterial count between a hamburger that's left out at room temperature and a hamburger that's kept refrigerated. The lab reinforces the concept that food must be properly chilled in order for it to remain safe to eat. This lab will be conducted as a teacher demonstration.

FOOD SAFETY Plate, Knife and Fork CONNECTION

Chilling is a critical method for controlling microbial growth. It does not kill microorganisms; therefore, it's important to properly handle meat when defrosting and cooking.

 

GETTING STARTED

MATERIALS

  • .5 pound (227 grams) package of inexpensive, raw hamburger
  • Dishwashing detergent for cleaning utensils and countertops
  • Disinfecting bleach solution (20 ml of liquid household bleach in 1 L of tap water, see Laboratory Procedures)
  • Knife for cutting hamburger package
  • 2 self-sealing plastic bags
  • 2 plates for hamburger packages
  • Paper towels
  • Safety gloves and lab aprons for anyone handling hamburger
  • 3 sterile Petri dishes with nutrient agar and covers
  • Sterile cotton swabs
  • Refrigerator or cooler with ice pack to keep the meat chilled
  • Lab Report Outline

ADVANCE PREPARATION

  • Purchase hamburger.
  • Disinfect the knife.
  • Divide the hamburger package in half by cutting through the package, including the meat and the bottom of the Styrofoam™ tray.
  • Put each half in a self-sealing bag and seal.
  • Label one bag "chilled" and refrigerate immediately.
  • Label the other bag "room temperature" and leave it out at room temperature at least overnight.
  • Be sure to put the packages on plates or in a bowl to prevent raw meat juices from leaking onto other food items in the refrigerator or onto the counter.
  • Make a photocopy of the Lab Report Outline for each student.

 

INTRODUCTION

You can use the following scenario as an introduction, or ask students to come up with a scenario of when meat might be unintentionally left out of the refrigerator for too long.

Suggested Scenario:
Last night, Mrs. Smith bought 2 packages of hamburger that she planned to cook for dinner. She put one package in the refrigerator. But then the phone rang, and other things occurred that distracted her. She forgot to put the other package of hamburger in the refrigerator. It sat out on the kitchen counter all night long. She woke up the next morning and placed the hamburger in the refrigerator, but wondered if the unrefrigerated hamburger was safe to eat.

Ask students: Would you eat the unrefrigerated hamburger? Why or why not? Let's test both hamburgers and see if there's any difference between them.

PROCEDURE

LAB 1 Conduct the Experiment

 

1. Have the class form a hypothesis about the properly refrigerated hamburger versus the hamburger left out at room temperature.
2. Now ask: How would you test your hypothesis? Record their answers.
3. Discuss a good experimental design for this lab.
4. Ask for three volunteers.

  • Remind them to wear safety gloves. They should take their sample near the center of the meat and away from the surface where the hamburger was cut. If possible, get a drop of hamburger juice.
  • Have one student label one Petri dish "control."
  • Have the second student label one dish "chilled." Have them swab the properly chilled hamburger, and inoculate the "chilled" dish.
  • Have the third student label one dish "room temperature." Swab the hamburger that was left out of the refrigerator, and inoculate the "room temperature" dish.

5. Tell the students that one package of hamburger was cut in half to make two packages. Then ask:

  • Why did we cut the package in half rather than just buying 2 individual packages? (To ensure that the meat tested is from the same batch, so as not to introduce another variable into the experiment)

6. Tape the dishes to seal them (see Laboratory Procedures).
7. Place the Petri dishes in the incubator at (35° C) for 1 to 2 days.

LAB 2 Observe, Record, and Summarize Results

 

This will be done at the beginning of the next day.

  1. Have the class discuss the results in relation to their hypothesis. Were there any surprises?
  2. Ask students: Did the cold kill the bacteria in the refrigerated sample? (There may be some bacterial growth, since cold doesn't kill bacteria.)
  3. What did you observe in the unrefrigerated sample? (Since the sample had remained in the "Danger Zone" for several hours, more bacteria grew than on the refrigerated sample.)
  4. What can you conclude about what went wrong along the Farm-to-Table Continuum in respect to this hamburger?
    • The burger may have been contaminated with bacteria before Ms. Smith purchased it. However, she compounded the problem by mishandling the meat after she brought it home. She did not follow the "Chill" rule of the 4 Cs of Food Safety - she violated the 2-hour rule by not placing the hamburger in the refrigerator immediately.
    • Who has the final responsibility for the safety of this burger? (It's our responsibility to make sure that food stays safe after we purchase it.)
  5. Could I just cook the unrefrigerated hamburger thoroughly and make it safe to eat? (No. If food is left unrefrigerated, bacteria cells will grow and more heat is required to kill the additional cells. Also, leaving the meat unrefrigerated invites the possibility of cross-contaminating surfaces, hands, etc. You should practice safe food-handling habits and always handle your food defensively. If the hamburger was left out at room temperature for more than 2 hours, it should have been discarded.)

Students can use the Lab Report Outline to record the results.

INSTANT REPLAY Time to review and summarize

1.What does the cold chain have to do with the things we learned in this lab? (We all need to continue the cold chain that started back on the farm in order to keep our food safe. Keep food chilled until it's ready to be cooked or eaten.)
2. Why do we freeze hamburger meat? (Freezing keeps food safe by causing foodborne illness microbes to enter a dormant stage.)
3. Does freezing kill bacteria? (No, freezing slows down the growth of harmful bacteria.)

RESOURCES

SciLinks Logo
Keyword: E-coli
Go to: www.scilinks.org disclaimer icon
Code: FS303

SUMMARY

To freeze or not to freeze, that is the question! Well, the answer is simple . . . to keep harmful bacteria from growing and multiplying, always store foods that won't be used right away in the refrigerator or freezer.

EXTENSIONS

  • Relate what you've learned about bacterial growth and chilling to other foods such as chicken, fish, seafood, eggs, etc.
  • Visit a local fast-food restaurant or supermarket and interview the manager to find out how he/she maintains the cold chain.
  • Relate your pathogen to this experiment and record the information in your food safety portfolio.
Career Connection icon with lab coat (large)

See real-life scientists in action!

  • Food Safety A to Z Reference Guide

 

UP NEXT . . .
Get ready for a scavenger hunt in our own kitchens. What will we be looking for? BACTERIA, of course!

 

Empty flask and half-filled test tube in a green circle as background (large)

CROSSED UP!

Time: Three 45-minute class periods

LAB AT A GLANCE

Students will discover that some items in their kitchens may be contaminated by bacteria. They will be challenged to hypothesize about where bacteria might be found in kitchens and which items might have the most and the least bacteria. Students will develop an awareness that bacteria can spread from surfaces to hands, and even to food, and will hypothesize how to control the spread of bacteria.

FOOD SAFETY Plate, Knife and Fork CONNECTION

Sponges, dishcloths, dish towels, can openers, refrigerator and faucet handles, countertops, and cutting boards are among the items in a kitchen that can spread bacteria if they are not cleaned properly.

 

LAB 1 Introduce the Experiment

 

ADVANCE PREPARATION

  • You may want to send home a note to explain the reason you're asking students to bring in items from their kitchens.
  • Bring in 1-gallon, sealable plastic bags for each student.

INTRODUCTION

Explain to students: Bacteria are everywhere, including in your very own kitchen! In this lab, you're going to become kitchen inspectors and look in your kitchens for things that may contain bacteria. 

Ask students:

  •  Where in your kitchen could bacteria be growing?
  • Could bacteria be on items that you or your parents use when preparing food? Make a list of students' responses.
    Some Probable Answers:
    - Sponges
    - Dish cloths
    - Dish towels
    - Pot scrubbers
    - Vegetable brushes
    - Can-opener blades
    - Sink stoppers or disposal covers
    - Paper towels
    - Utensils
    - Cutting boards
    - Dishes
  • Now, ask students to hypothesize about which kitchen items contain the most bacteria and which contain the least bacteria. Make 2 lists: "Most Bac" and "Least Bac." Ask them: Why would/wouldn't bacteria be found on these items?
  • Then ask students to vote on the items most and least likely to harbor bacteria. List the Top 5 items in each category. Keep the Top 5 lists on the board through the next few labs so students can compare their lab results with the lists.
  • Group students into teams of 3 to 4. Ask each team to choose at least 3 or 4 kitchen items they want to inspect.
    - Students should include items they think will have lots of bacteria as well as those they think will have fewer bacteria. For example, they may want to compare new sponges or just-washed dishcloths with dirty or just-used sponges or dishcloths.
    - Items don't have to be taken from the class list. Teams can pick their own items to investigate. Try for as many different items as possible but make sure the important ones, such as sponges, dish cloths and dish towels, are included by at least 2 teams.
  • Give each team 1-gallon storage bags to take home. Ask them to bring in kitchen items from home to test. Students should ask their parents' permission to bring the items to class. Ask them to put in 1 item per bag, seal the bag, and bring it to class.

Note: This experiment should be set up to avoid any comparing and critiquing of items from students' homes. Put a number on each bag as students give them to you. Write each student's name on a list with their corresponding bag number. The experiment should be a general learning experience about how to avoid cross-contamination in the kitchen, not a specific review of individual items. For example, students should look for common items that are most likely to harbor bacteria.

LAB 2 Develop, Hypothesize, and Conduct Experiment

 

GETTING STARTED

ADVANCE PREPARATION

  • Bring in extra kitchen items for students who weren't able to bring items.
  • Photocopy Lab Report Outline for each student.

MATERIALS

For the class

  • Distilled water - 2 gallons
  • Disinfectant bleach solution (20 ml of liquid household bleach in 1 L of tap water, see Laboratory Procedures)

For Each Team of 3 to 4 Students

  • 2 to 3 sterile Petri dishes with nutrient agar and covers
  • Permanent marker
  • Sterile cotton swabs
  • Parafilm or masking tape to seal dishes

 

SAFETY FIRST

 

  • Seal all inoculated Petri dishes with Parafilm or masking tape. Remind students never to open a dish with organisms growing in it. Some organisms could be dangerous pathogens.
  • Destroy all disposable Petri dishes using safe techniques after the experiment is completed, or soak each Petri dish in a bleach solution after using it ( 9).
  • Disinfect all lab surfaces before and after working in the lab (see Laboratory Procedures).
  • Wash your hands before and after the lab experiment.

 

PROCEDURE

  1. Ask each student to label their storage bags by the type of item (e.g., sponge, can opener, etc.). Students' names should not be put on the bags.
  2. Have each team develop a hypothesis and design an experiment to test their hypothesis.
  3. Pose these questions to guide students through their experiments:
    •  Which type of kitchen items might have the most/least bacteria? Why?
    • How can you find out which items have the most/least bacteria? (Swab the items and inoculate the Petri dishes.)
    • What's a good way to get a sample of the bacteria in these items? (Swab the item directly, or add water to the bags and sample the water.)
    • What kind of water would be best to use? (Sterile or distilled water)
    • How can you transfer bacteria from the kitchen item to the water? (Squeeze/massage the item in the bag.)
    • What does the water look like after you squeeze/massage the item? (The water in some bags will appear very dirty. Water in other bags will appear clean.)
    • Is the appearance of the water an indication that bacteria are present? (Not necessarily)
    • How can you be sure you're not introducing new bacteria to the test samples? (Use sterile plates and swabs. Use a control bag with distilled or sterile water.)
  4. Demonstrate how to sample the water and inoculate agar plates (see Laboratory Procedures).
  5. Discuss the importance of a control plate. To test for bacteria in the water, swab half of the control plate with distilled water. Leave the other half untouched.
  6. Review the important rules of lab safety, especially the handling of inoculated Petri dishes (see Safety First in the Laboratory).
  7. Let each team develop their hypothesis and design their experiment.
  8. Let the students conduct their experiments.

LAB 3 Observe and Record Results

 

PROCEDURE

  1. Have teams observe their Petri dishes and record the results on a data table.
  2. Ask each team to present their findings to the class. List the class results and have the students compare their findings to the "Most Bac" and "Least Bac" lists from Lab 1. (Be sure to focus the discussion on the categories of items and not specific items.)
  3. Pose questions to guide students through a discussion. For example:
    •  How did your original lists compare to the test results? Were there any surprises? What are your conclusions?
    •  Could bacteria transfer from kitchen items to your food? Your hands? What might happen in these cases?
    •  Why do certain kitchen items have more bacterial growth than others?
    •  How do the data you collected relate to the 4 Cs of Food Safety? Which of the 4 Cs?
    •  How could you reduce the bacteria on the items you tested?
    •  What are your suggestions for avoiding cross-contamination in the kitchen?• What advice would you give to family members to help them prevent the spread of foodborne bacteria?

INSTANT REPLAY Time to review and summarize

  1. Did you find any bacteria? Where? Were you surprised with your findings? Why or why not?
  2. Why is it a problem to find bacteria on a kitchen sponge, dish cloth, dish towel, etc.? (Bacteria from these items can spread to other surfaces and then to food.)
  3. To what surfaces can the bacteria spread? (Cutting boards, utensils, kitchen equipment, countertops, etc.) How can bacteria spread from your hands to other things? (Bacteria can spread from your hands to other things when contaminated hands touch those surfaces.)
  4. What can you do to prevent cross-contamination? (Wash your hands thoroughly, frequently wash sponges, dish cloths, dish towels, cutting boards, countertops, and cooking utensils with hot, soapy water.)
  5. What can you personally do to reduce the spread of bacteria in your kitchen at home? (Follow the 4 Cs - especially Clean and Combat Cross-Contamination. See the 4 Cs section in the Food Safety A to Z Reference Guide.)
  6. Did you discover that you were "guilty" of any unsafe practices in the kitchen? If so, what's your strategy for correcting those unsafe practices?
  7. How do your findings from this lab relate to the Bacteria Everywhere lab in Module 1 - Understanding Bacteria? (They show that bacteria are everywhere and can spread from hands to surfaces and to food.)

RESOURCES

SciLinks Logo
Keyword: E-coli
Go to:
www.scilinks.org disclaimer icon
Code:
FS303

SUMMARY

Bacteria can spread from kitchen items to hands, and even to food. The spread of bacteria can be controlled through proper cleaning.

EXTENSIONS

  • Develop a Home Food Safety Survey based on the results of your investigation. Give the survey to at least 5 family members, friends, relatives, or neighbors to survey their kitchens. Tally the answers.
  • Using the survey results, develop a "kitchen safety" brochure or Web page explaining how to prevent cross-contamination in the kitchen.
  • Use your food-safety portfolio to record how your foodborne pathogen relates to your findings from this experiment.
Career Connection icon with lab coat (large)

See real-life scientists in action!

  • Food Safety A to Z Reference Guide

 

UP NEXT . . .
Give yourself a hand for successfully completing this lab, and prepare to use your hands in the next exciting lab experiment - one that will leave you glowing in the dark!

 

Flask and Test Tube Icon - large

HANDS OFF, BACTERIA!

Time: Two 45-minute class periods

LAB AT A GLANCE

This experiment challenges students to identify variables involved in handwashing. They will design experiments to discover the best method for washing their hands to reduce the spread of bacteria. Students will also analyze and present the data.

FOOD SAFETY Plate, Knife and Fork CONNECTION

Dirty hands are one of the quickest ways to spread harmful bacteria and expose yourself and others to the risk of foodborne illness. Careful attention to washing hands thoroughly is essential for good health.

 

GETTING STARTED

MATERIALS

  • Glo-Germ™ (see Resources) and ultraviolet light

T I P S

Cinnamon, along with cooking oil can be used in place of Glo-Germ™ and ultraviolet light. If using cinnamon, rub 1 tablespoon of cooking oil all over your hands until completely coated. Sprinkle 1 teaspoon of cinnamon on hands and rub it around until it's evenly distributed. The cinnamon can represent bacteria.

  • Handwashing soap
  • Paper towels
  • A source of running water
  • Petri dishes with nutrient agar and covers for each team of 3 to 4 students (optional)
  • Dr. X and the Quest for Food Safety video/DVD, Module 4 - Retail and Home

ADVANCE PREPARATION

  • Gather a collection of materials for students to use in their lab designs.
  • Put Glo-Germ™ (or cooking oil and cinnamon on your right hand just before the students enter the classroom.

SAFETY FIRST

 

  • Wash your hands before and after the lab.
  • Seal all inoculated Petri dishes with Parafilm or masking tape. Remind students never to open a dish with organisms growing in it. Some organisms could be dangerous pathogens.
  • Destroy all disposable Petri dishes using safe techniques after the experiment is completed, or soak each used Petri dish in a bleach solution (see Laboratory Procedures).
  • Disinfect all lab surfaces before and after working in the lab (see Laboratory Procedures).

 

INTRODUCTION

Greet each student with a hearty handshake as he/she enters the classroom. (Only you know at this point that Glo-Germ™ is on your hand.) When the students get settled, ask them:

  •  When was the last time you washed your hands?
  •  What have you touched since then? What have you touched in the past 2 hours? In the past 4 hours?
  • Do you think your hands have picked up bacteria recently? (Let the students discuss the things they touched in the last few hours. Hopefully, someone will remember that you shook everyone's hand.)
  • Could I have spread bacteria to your hands through my handshake? Let's find out. (Now take out the ultraviolet light and let the students examine their hands and classroom surfaces.)
  •  How many people or surfaces have come in contact with my "bacteria" without coming in contact with me?
  •  Would you want to eat a sandwich made by people who didn't wash their hands? Why?
  • Have you ever seen signs in restaurant bathrooms stating, "Employees must wash hands before returning to work"? Why are these signs so important? (One of the most common ways to transmit foodborne bacteria is by using the bathroom, not properly washing your hands, and then touching food.)

    Note:
    For a real-life outbreak case involving a foodworker who did not properly wash his hands, see the Outbreak Alert activity.

We know that handwashing is extremely important. Today we're going to do a scientific investigation to learn more about the role handwashing plays in helping keep us healthy and our food safe. Let's begin our investigation . . .

LAB 1 Design the Experiment

 

PROCEDURE

  1. Ask students the following:
    •  What are some of the different variables involved in handwashing?
      (Washing or not washing, using soap or no soap, the time spent washing hands, the temperature of the water, scrubbing hands versus just rinsing.) Have students develop an experiment to discover the best method for washing their hands.
    • How could we test whether or not handwashing has been effective?
      (To determine the most effective handwashing techniques, you can use Glo-Germ ™ and an ultraviolet light or cinnamon and cooking oil to represent "bacteria.") Students can test which of the following actions get rid of the most bacteria:
      • cold versus warm versus hot water
      • scrubbing versus not scrubbing hands
      • using soap versus not using soap
      • length of time spent scrubbing (20 seconds is the recommended amount of time for effective handwashing)
        Note: Students can also use Petri dishes to sample hands before and after handwashing.
  2. Have students form teams of 3 to 4 students. Ask each team to design an experiment or activity to investigate handwashing. They can choose to show how germs are spread by poor handwashing habits, the effectiveness of different handwashing techniques in reducing bacteria , or they can investigate their own handwashing hypothesis.
  3. Have students write down their research question, hypothesis, and the procedure they plan to use. Challenge them to include the scientific principle behind their findings.
  4. Let each team present their hypothesis and experimental design to the class. Encourage all students to discuss the merits of each suggested test. After the class discussion, give the teams time to revise their hypotheses and experimental designs if they wish to.

LAB 2 Conduct the Experiment and Record and Report Results

 

PROCEDURE

  1. Have students conduct their experiments.
  2. Ask students to observe and record their results, and then create a chart or graph to show the data from their experiments.Complete the lab by having the teams write their conclusions.
  3. Have the teams present the results to their experiments. Encourage students to include any problems they may have had and what they would do next time to avoid those problems. Remind students to explain the science behind their discoveries.

INSTANT REPLAY - Time to review and summarize

  1.  How do bacteria spread? (They can spread from person to person, from people to foods and objects.)
  2. What methods worked best to remove "bacteria" from your hands?
  3. Why do certain methods (e.g., scrubbing time, use of soap, etc.) work better to remove bacteria than others?
  4. Did your experiment give you any ideas for conducting further research on handwashing?

Video tape in a green circle background TIME TO TUNE IN ...Module 4 - Retail and Home Part 2 - Home

Let's rejoin Dr. X to see why he's so concerned about a problem in Sector 17
Show video/DVD Module 4. Part 2 - Home (Time: 2 minutes).

  • The Barkley family learned about the importance of washing their hands. What could have contaminated their hands before they sat down to eat dinner? (Playing with the dog, sneezing into hands, taking out the garbage, and playing basketball)
  • Why is handwashing so important both at home and in the retail setting? (Our hands are in contact with bacteria in all settings. It's necessary to wash them just before food preparation, whether at home or in a retail setting.)
  • Can you think of other things that you touch that contribute to the spread of bacteria? (Students should contribute their own answers.)

SOAP + SCRUBBING ACTION + HOT WATER = CLEAN HANDS!

  • The soap suspends dirt and soils.
  • The rubbing motion helps pull dirt and greasy and oily soils free from your skin so germs can be washed away.
  • Hot running water washes away suspended dirt and soils that trap germs.

DID YOU KNOW?

 

  • 20% of consumers don't wash their hands before preparing food.
  • If you don't wash your hands, you could cause infant diarrhea! Your hands can pick up bacteria from the following things and spread bacteria to the baby:
    • Diapers
    • Raw meat, poultry, eggs, and seafood;
    • Animals such as dogs, cats, turtles, snakes, and birds; and seafood;
    • Soil

Note:For more handwashing tips, see the 4 Cs section in the Food Safety A to Z Reference Guide.

 

FINGER TIPS

Use these tips to keep your hands squeaky clean!

  • Make sure there's handwashing soap and paper towels or clean cloth towels at every sink in your home.
  • Wash your hands with hot, soapy water (for at least 20 seconds) before and after handling food and after using the bathroom, changing diapers, and handling pets. Thoroughly scrubs hands, wrists, fingernails, and in between fingers. Rinse and dry hands with a paper towel or a clean cloth towel.
  • ALWAYS wash hands after touching raw meat, poultry, seafood, eggs, or unwashed fresh produce.

 

HANDS OFF, BACTERIA!

SUMMARY

Hands are one part of the body that are most exposed to microorganisms because they touch many things every day. Thorough handwashing with hot, soapy water removes bacteria from hands.

EXTENSIONS

  • Create a brochure on handwashing for young children.
  • Set up an appointment to talk at an elementary school or preschool, a nursing home, Girl or Boy Scout meeting, PTA group, etc. Demonstrate the GLO-Germ™ activity in relation to food safety.
  • Contact a local health center or doctor's office to find out their handwashing policies.
  • Relate the results of this activity to your foodborne pathogen and record the data in your food safety portfolio.

DON'T FORGET!

It's time for students to share their food journey charts from the Chain of Food activity (Module 2) with the rest of the class.

 

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See real-life scientists in action!

  • Food Safety A to Z Reference Guide

 

UP NEXT
Are you ready for your next mission? An Outbreak of a foodborne illness has occurred across the country. In the next activity, you and your FBI FoodBorne Illness) team will uncover the clues and discover the source of the outbreak.