Back to school: Keeping lunches out of the danger zone
By Mary Hightower
U of Arkansas System Division of Agriculture
July 14, 2025
Fast facts
- Temperature danger zone is between 40-140 degrees F
- Smith tests tactics for keep cold lunches cold, hot lunches hot
(915 words)
(Newsrooms: with art of Smith, vintage school lunchbox)
BERRYVILLE, Ark. — Once a school lunch leaves your home kitchen, will it still be safe when lunchtime rolls around?
That’s the question Torrie Smith, Carroll County extension agent in family and consumer sciences, wanted to answer.
So, she did a little experimenting.
“I have young children that will soon go off to school and will want to take a packed lunch. I know one of the top priorities for moms is packing a nutritious lunch that your child will actually eat,” she said. “A major concern should be, will your child’s school lunch be food safe by the time they get to lunch?”
At issue is TDZ — the temperature danger zone — the zone between 40 and 140 degrees Fahrenheit where foodborne pathogens multiply most rapidly.
“Depending on what time you or your child packs their lunch and what time it is eaten determines how long it needs to stay out of the temperature danger zone,” Smith said. “The food might need to keep cool, or hot, for anywhere between five to six hours.”
Smith bought a bunch of color-coded, insulated fabric lunchboxes and divvied them into cold and hot lunches and went to work.
For the cold lunches, each box got a turkey and cheese sandwich with mustard, and carrots as a side. Two of the boxes also got a cheese stick. She placed a frozen yogurt tube in one lunch to act as a cold pack to keep the temperatures low.
- Red lunchbox. In the first lunchbox, she used a commercial freezer pack to keep it cold.
- Blue lunchbox. In the second lunchbox, she used the frozen yogurt tube. Smith said the manufacturer advertises that the tube can keep the food cold and can be eaten when defrosted.
- Orange lunchbox. In the last cold lunch, she used a baggie filled with ice. Not everyone has access to a commercial freezer pack, but a family might have ice to make a homemade cold pack.
For the hot lunches, Smith packed a container of noodle soup, whole wheat crackers, carrots and a cheese stick.
“Most young children won’t have access to a microwave to heat up their lunch so it’s up to the lunch packer to heat up the soup, pasta, or other hot item while packing and keep it hot until lunch,” she said.
- Green lunchbox. In the first hot lunchbox, Smith put the soup in a glass bowl with a lid, without any special insulation added.
- Purple lunchbox. In the other hot lunch, Smith used an insulated stainless-steel Thermos-type vacuum bottle to keep the soup hot. “I made sure to get one that wasn’t too heavy that wouldn’t weigh down a small child,” she said.
Watching the clock
Then she waited, with kitchen thermometer in hand.
“I set the lunches aside and planned to check the temperature of the lunches every two hours until I reached six hours when the lunch might be eaten,” Smith said. “I didn’t put the lunches in the refrigerator because not a lot of teachers have a big enough fridge to store every child’s lunch.
“After the first two hours, I used my thermometer to check each sandwich, soup, and cheese stick to test the temperature,” she said.
The results
Smith didn’t have to wait long for the results, and what she found was surprising.
“All of the lunches were in the temperature danger zone at the two-hour mark,” Smith said.
“None of the methods I used to keep the cold lunches cold kept the cold lunches out of the TDZ and the same is true for the hot lunches.
“Bacteria loves to grow in the TDZ and can make your child very sick,” Smith said. “While foods can be at the TDZ for around two hours and still be safe, by lunchtime, the food would have been in the TDZ for over three hours.”
Smith offered these tips for making sure lunches remain safe after the two-hour mark:
- Use two sources of cold. According to the U.S. Department of Agriculture, there is a better chance the lunch is going to stay cold enough to be safe with two cold packs.
- Freeze the drink. Hel keep the lunch cold by freezing a 100 percent fruit juice box or small water to act as another cold source. Not only will it help in keeping the lunch cold it will also ensure their drink to be cool and refreshing by the time lunch comes.
- Pack smart. Put the most perishable items right next to the ice pack. Doing this will make sure the items most likely to grow bacteria — foods with dairy and mayonnaise, for example — in the TDZ are kept the coldest.
- Preheat the thermos. Before putting hot foods in an insulated thermos, preheat it by filling it with boiling water and letting it set for a few minutes. After the thermos is warm, dump the water, immediately add the hot food, and quickly place the lid tightly on the thermos.
- Keep it clean. Do not reuse plastic baggies intended for single-use. The resealable baggies can harbor bacteria that cause sickness. To reduce single-use plastic waste, an option is a bag that is washable can be sanitized. If the lunch is for a small child, discuss with the child what is to keep or throw away.
Find Smith’s original blog post on safe lunches and other helpful advice online at Torrie’s Top Tips. Find safe lunch tips from the U.S. Department of Agriculture.
Product mentions do not imply endorsement by the University of Arkansas System Division of Agriculture.
To learn about extension programs in Arkansas, contact your local Cooperative Extension Service agent or visit www.uaex.uada.edu. Follow us on X and Instagram at @AR_Extension. To learn more about Division of Agriculture research, visit the Arkansas Agricultural Experiment Station website: https://aaes.uada.edu/. Follow on X at @ArkAgResearch. To learn more about the Division of Agriculture, visit https://uada.edu/. Follow us on X at @AgInArk.
About the Division of Agriculture
The University of Arkansas System Division of Agriculture’s mission is to strengthen agriculture, communities, and families by connecting trusted research to the adoption of best practices. Through the Agricultural Experiment Station and the Cooperative Extension Service, the Division of Agriculture conducts research and extension work within the nation’s historic land grant education system.
The Division of Agriculture is one of 20 entities within the University of Arkansas
System. It has offices in all 75 counties in Arkansas and faculty on three campuses.
Pursuant to 7 CFR § 15.3, the University of Arkansas System Division of Agriculture
offers all its Extension and Research programs and services (including employment)
without regard to race, color, sex, national origin, religion, age, disability, marital
or veteran status, genetic information, sexual preference, pregnancy or any other
legally protected status, and is an equal opportunity institution.
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Media Contact: Mary Hightower
mhightower@uada.edu