Science and Our Food Supply: Investigating Food Safety from Farm to Table

6. 

Use Parafilm to seal the dishes (see page 8).

7. 

Place the Petri dishes in the incubator at 95° F (35° C) or 

let dishes sit at room temperature (away from the sun) 

for 1 to 2 days. 

 MODULE 4:

 RETAIL AND HOME

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68

MIDDLE LEVEL

MODULE 4:

 RETAIL AND HOME

A CHILLING INVESTIGATION

2

LAB:

 OBSERVE, RECORD, AND SUMMARIZE RESULTS   

At the beginning of the next day, ask students to observe and 

record results. 

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 hamburger 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. Meat that is left out 

too long can accumulate bacterial toxins that may not 

be destroyed by additional cooking. 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 (page 23) to record the results. 

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.)